Observed trials bike designing

The motor (+flywheel mass spin up) and clutch engagement dynamic is a interesting one. Need to think on it a bit to get a better visual on all the factors at play. Your certainly looking for a good solid kick for many of the moves. No matter how strong a soccer player you are, you get very little distance kicking the ball if your foot starts right against the ball and then accelerates vs winding up a bit and hitting it with the foot and your mass moving.
I like the kicking analogy.

When I was riding today I was paying attention to this a fair bit and it really struck me strongly how important the RPM is to the reaction you want. Sometimes you don't need much power at all, but you do need the back wheel to really snap around quickly - to zap the back across a gap for instance. Other times you build RPM to get power and then feed it in a little slower with the clutch - driving in to a tall but not vertical step say. It's very often the case that you rev the bike well past what you think you need and then deliver off the clutch, nothing worse than running out of power half way up, or needing to add power when traction is already tenuous. I'm struggling to visualise how all that would work on a fully virtual clutch.

I also noticed just how often I land onto the rear with a slipping clutch. The clutch controls the power to the wheel, but the RPM is varying. Sometimes it's rising as you prepare for the next move, other times it's falling as you let the excess energy decay away. Sometimes you let the energy decay a certain amount, then when it sounds about right give the clutch a quick flick for a small correction or extra movement.
Amazing how our brains can process all that's going on.
 
Correct about the flywheel. I was suggesting some kind of gear reduction such that the clutch cant tell the difference. Basically from the flywheel back its business as usual. Should give you the ability to duplicate the exact feel you are used to. You could even put a noise making device on the flywheel so the rpm note is the same as what you are used to. This would allow something like a 15000rpm astroflight or other high quality small motor to be a functional stand in for the gas motor. Seems to me a small motor capable of high power and low torque would be the closest match to a gas motor. Just trying to avoid dealing with a 15000 flywheel.

Drawbacks to this approach are complexity weight and friction from extra reductions. Maybe there is a happy medium. Little more torque in exchange for losing a few gears.

As for electronically matching the torque of a gas motor, it does seem like a shame to take away what the electric motor is good at. The issue is that trials is so reliant on precise feel and familiarity with existing architecture that it may be necessary if you want to truly ride it exactly the same. I think we are all very used to the ramp rate and available torque of gas motors at a wide range of rpms.

There is a little wiggle room like how the higher torque can probably help consolidate some of the gears. Maybe in the fast gear you really unclamp the current limits and let the torque do the work that 3rd-5th gear used to do.

All sports evolve with the equipment. Maybe some of the moves you arent seeing in etrials are not necessary with more torque and no consequences for stalling. It will be interesting to see if the electric bikes on the market continue to lag behind their ICE counterparts or if people just haven't figured them out yet.

Hard to know if EM is designing that 4speed bike because thats the best way to do it or if they are doing it to make the transition less scary for customers. Just look at all those Brammo bikes that were shifted through the gears once and then just left in 3rd or 4th gear forever.
 
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@DanGT86 I've looked at the AstroFlight 4535 a few times - it's an interesting option. I probably should email Astro and get some more details on it. 15kW is kind of borderline I think, probably depends on it's characteristics I guess. I've also been a bit wary that the default version is open frame and fan cooled, not sure if a closed version would need to be de-rated. It's also a lot of money to throw at an experiment. Don't know if you don't ask though.
I'll have to do some calcs and see what sort of max RPM is realistic for a non-exotic flywheel. 15,000 certainly should be in the realms of sanity for a quality steel I'm guessing, so no need for reduction gearing. The double ended shaft option would be nice too, if the little 1/2" shaft can take the load being passed through it from flywheel to output gear. A beefier shaft would also make me a bit more comfortable.

My experience and general reports from others on e-trials is that there's no problem adopting to the nature of electric power/torque curves. If anything they are felt to be an improvement in almost all areas. As you can so easily adjust the throttle response it's all good. The problem comes when you want smooth progressive throttle but really sharp clutch. It's wanting both ends of the spectrum at the same time that causes so much difficulty. Plus issues around fast spin-up when you lose traction.
I find that as I get better at using clutch I care less and less about how the motor operates - just spin it up and use clutch for virtually all the control. The main things are that it can spin up the flywheel quickly enough, and that it is smooth & solid down near idle. The rest of it I barely notice. And it's similar when I go to the e-trials, it's only at the ends of the performance that I take much notice, the bit in the middle is - whatever.

I expect that riding will evolve as electric becomes the predominant machine. I fully expect there'll be some completely new techniques developed over time as a new generation grows up on high performance e-trials.
I just don't think the present crop of bikes have got to the point where they are even comparable to ICE bikes, let alone able to start moving beyond them.
The acid test is that e-trials still aren't able to compete head to head with ICE bikes beyond basically Club or Regional level. Once you start playing with the kids who are pushing for a spot on the world stage the EM's etc are just out of the picture really.
It'll happen, no doubt. ICE trials bikes are Dodo's that just haven't fallen off their perches yet. It amazes me when I talk to trials riders who can't see that and who seem to think ICE trials bikes will remain the pinnacle of the sport for decades to come. Blind.

EM have spent years with single speed bikes. They've sold thousands and are unquestionably the dominant brand. Most people don't even consider that they might benefit from gears.
If they're going to multiple gears it's because they think it makes the bike perform better, no question at all in my mind.
As I said, I can't see a lot of point in gears on a road machine. Look at all the EV's that are single gear and clearly perform as well or better than just about any comparable ICE car or bike. That said, some of the really high performance cars are going to 2-speed boxes.
Trials is just such a different use case, to me 2 or 3 gears are a no-brainer.
 
Bikerpete,

Yes,the flywheel contributes gyroscopic forces(P-factors) and so do the rear wheel and front wheel. Stability is sometimes good, but often a hinderance for making changes..

If convenient, would you measure a trials bike flywheel/clutch/plate and report the dimensions (OD, ID, thickness, material(alum or steel) and the size of other hollows)? Please report them on this thread? I want to calculate the second moment of inertia for that rotating mass. I would have to tear apart a motor to get these dimensions
— Thanks

I have fronts and rear rims with tires on them, so I can calculate the second moment of inertia of each wheel.

Also, what is typical max rpm you might start at when doing a maneuver using clutch modulation? The weight of your bike would also aid in some calculations.

There has been one hell of lot empty talk going on this thread and virtually zero calculations about the momentum transfer physics. It seems few thread participants realize that inertial rotating mass is proportional to the square of the radius of rotation. The little high RPM flywheel likely does not exhibit much more angular moment that 2 rotating wheels?

Let’s put the knife through the coffin [black box for the flywheel]?

I call my approach “Delta P + heuristics” using 2 manual controls. OR the sum of the momentum changes for a short time interval is equal to the sum of the impulses. Forget energy methods as the system does not conserve energy.
 
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DMG, thanks for the number crunching. I posted a simple flywheel calculator a while back. I see we can first combine some components. The clutch basket backer plate can act also as a flywheel. You can get as fancy as you wish with it but for starters a simple metal plate should be good for your crunching. I picture it a thicker outer ring, and having it somewhat decoupled from its hub as on a floating brake rotor setup. It would be directly mounted to the motor and encased as Pete wants to hold oil. It would spin at motor speed so a bit faster than a ice setup. Matching the motors diameter with a steel ring flywheel will add boat loads of moment. Bunch of folks doing calcs on them and not seeing anyone worried about issues below the 20000 RPM region. We are near half that here. Just for numbers, a plate 8 -10mm thick and on the plus side of the diameter of the clutch. Thinking one could turn a large steel caster wheel into a usable shape to encase the clutch on one side.

From there, a simple two speed jack shaft or a pair of them for four speeds.

For the Kick dynamic, something more is connecting for me. Back to this shortly with something that may stimulate some deeper understanding..
 
I like your approach DingusMcGee!

I would love to get some precise dyno runs of the bike and motor we are theoretically copying. I think a lot of these targets would be easier to hit with that.

Also, datalogs of a bike being ridden would be useful.
  1. Throttle position
  2. rpm
  3. Tire Rpm for both wheels
  4. engine vacuum and or load
  5. Slow motion vid of the bike and rider with synched clock and datalog to watch suspension and tire action.
All of these things would help a lot. It would clearly parse out whether its the engine torque or the flywheel mass providing the torque.

This data collection and analysis is the only real way to get this right on the first few tries. It would be expensive. I can't imagine the production companies like EM are not already doing this. If they are not then I might need to go get a new job.

Bikerpete, I would definitely not put the flywheel on the opposite side of the motor as the output shaft. Sending those torque shock loads through a 1/2 shaft would definitely destroy it. With the flywheel on the output shaft the shaft is never experiencing any more load than the maximum output torque of the motor which it is designed for.
 
I think a virtual flywheel controller could be implemented with only knowledge of throttle position and clutch position. You track the angular velocity of the "flywheel." Throttle inputs add energy to the flywheel while clutch inputs take it away (provided the flywheel is spinning fast enough to make torque). There is a configurable decay to the flywheel energy to slow it down. The output of the controller is the actual torque command to the motor controller.
 
OK. Been off doing other things so just catching up with the activity here.

@DingusMcGee in order fo your questions:
  • Wheel inertia is totally irrelevant - when we're talking balancing a trials bike we are absolutely, totally stationary. If you're moving even a 0.5kmh it's riding, not balancing in the trials world. A spinning flywheel doesn't in any way turn a bike into a self-balancing device, but when you're talking about people with the ability to stand balanced on their bikes with one or no hands on the handlebars, folding out the kick start and firing up a 300cc single, then looking over their shoulder to see if the back wheel is exactly where they want it, then a small advantage is very noticeable. There are trials riders who can balance on their bike, put their head where a seat would normally be (trials bikes don't have those superfluous jiggers) and roll up into a headstand, still balancing the bike. Trials is a different world to most bike riding.
  • I can't give you complete numbers because the crankshaft plates are significant contributors to rotational inertia in a trials bike and I've never measured or seen measurements for them. I'd guess you could approximate those plates at 100mm dia and 12mm thick, times two. A trials flywheel varies between makes and models, but you could call the MoI 11,000 kg*mm^2 and not be too far either side of several bikes. The flywheels are steel cups. Below are a few samples. Density is an approximation allowing for the magnets embedded in the flywheel. Figures below were verified by doing inclined plane rolling tests - results were within reasonable error.
  • OD​
    ID​
    Width​
    Volume​
    Density​
    Weight​
    Weight​
    MoI​
    mm​
    mm​
    mm​
    Cm^3​
    g/cm^3​
    kg​
    pounds​
    kg*mm^2​
    139.2​
    85.5​
    46​
    435.94​
    7.83​
    3.413​
    7.509​
    11387​
    136.5​
    85.5​
    46​
    409.04​
    7.83​
    3.203​
    7.046​
    10386​
    146.0​
    100​
    42​
    373.28​
    7.83​
    2.923​
    6.430​
    11441​
  • RPM - pick any number you like :) As I said, sometimes we're using clutch and flywheel virtually at idle (900rpm) other times it's hold the throttle pinned until the engine reaches constant RPM and wont accelerate further. Call it 9,000 rpm as a reasonable figure.
  • Forget about the clutch. Only the basket is rotating when the bike is stationary and it's a puny little piece of aluminium that's maybe a couple of hundred grams, I can't recall the reduction of the primary gears, but maybe 4.5:1? So clutch contribution to inertia is zip diddly. Forget it.
  • Trials bikes are approx 67kg +/- a couple kg.
I've seen other people do various calcs on some of this stuff, can't recall where now. But I have seen figures that show a typical trials flywheel at 6000rpm can lift 300lb several feet.
Here is a pic of a YZ250 motocross flywheel, and a 250 trials flywheel. Vastly more mass out at the periphery!

@DanGT86
It would clearly parse out whether its the engine torque or the flywheel mass providing the torque.
I've said it before a bunch of times, and no doubt I'll say it again. The throttle is very often completely closed when the clutch is released. The engine contributes stuff all to the take-off torque in most cases.
Very advanced riders will hold throttle open for the very first part of the launch on really big stuff, but just take a look at a few videos of riders launching onto big stuff then try to imagine how you're going to hold the throttle open when your hips are between the handlebar grips! Yes, on the big stuff before they go they release the throttle tube, cock their wrist over the top then grab hold again so they can keep it open longer, but this is really very advanced. Mere mortals usually drive their wrist down, hold the throttle open then extend up. Your hand unwinds the throttle as you go, and the clutch release has to be late in your extension to get the reaction you need from the bike.
Somewhere I've got videos where I deliberately rev the bike up, shut the throttle completely, pause, then Go. Guaranteed no throttle and a decaying RPM. The bike still gets airborne and climbs out on the obstacle. All flywheel except for whatever torque the engine at fully closed throttle produces. Heck, I've done the same on my electric trials while testing bigger flywheels. In that case there is ZERO power out of the motor and the bike still gets airborne.
Bikerpete, I would definitely not put the flywheel on the opposite side of the motor as the output shaft. Sending those torque shock loads through a 1/2 shaft would definitely destroy it. With the flywheel on the output shaft the shaft is never experiencing any more load than the maximum output torque of the motor which it is designed for.
My thoughts exactly. But the problem is putting the flywheel on the same end as the clutch makes it really, really hard. I've done that on my QS138, but it's not pretty.
It actually amazes me that 2-stroke cranks can withstand it. Crankshafts are 5 pieces - two main shaft halves pressed into the crank plates, then a crank pin pressed into the two plates with the conrod running on it. It's all interference fits, no splines. You can press the crank pin apart, replace the conrod bearings and press it back together and it all still works. That's with the flywheel on the opposite end of the shaft to the primary gear. It obviously works just fine, but it surprises me every time I see it.

But a 1/2" shaft is looking wildly optimistic to me! That's one of the reasons I go back to AstroFlight, then discount them again, and again. Disappointing. It's pretty obvious those motors are primarily designed to run something like an aviation prop -skinny little parrallel shaft with not even a flat, let alone a keyway.
And it's not quite true all the shaft experiences is motor torque if the flywheel is on the output end - in a geared drive there's going to be significant bending moment on the shaft too.

Throttle inputs add energy to the flywheel while clutch inputs take it away (provided the flywheel is spinning fast enough to make torque)
Nup. Completely falls over when you've got the throttle closed and you dump the "clutch". Zero throttle energy minus some figure from the clutch isn't going to get you very excited, or far up a 6 foot step.

Refer back to discussion above about closed throttle. This isn't optional, it's simple biomechanics, even if you disregard the fact that the best trials riders in the world use some form of that technique which suggests it's got just a little bit of value and shouldn't be chucked away just because we're moving electrons rather than hydrocarbons.
And look back here and elsewhere - EM did almost exactly that with the 5.7 - you could wind on throttle, but clutch cancelled it. Then drop the clutch and whatever throttle setting you had went straight to the motor. Hopeless. OK for beginners and low intermediate level, but totally useless beyond that. For many reasons that I really can't be bothered going into because it would take far too long and open a discussion I don't want to get engaged in.
Maybe it could be improved upon as Dingus is talking about, but I have to admit to being rather skeptical.

I've little interest in getting rid of a physical flywheel and a decent friction clutch, they just work so well. I am interested in seeing if electronics could effectively make that physical flywheel response adjustable.

I was going to ask this elsewhere, and probably will.
Does anyone have any ideas how you could approximate power consumption with only throttle input and RPM?
I don't need it to be accurate, I'm just thinking some figure that varies somewhat proportionally to real motor output. The number itself doesn't matter as long as I could apply a factor (experimentally field derived) that made that number useful to modify the slope of the RPM decay rate according to throttle position.
I'm considering the situation when you release the clutch with a progressively closing throttle - the decay rate slope will get steeper as throttle closes and motor power drops.
It's kind of icing on the cake, not so important for initial experiments.
 
Bikerpete,

Thanks mucho for gathering the flywheel data. I am of the intuition that a TB operator’s changes of any significance to the adjustment of the clutch/throttle occur no faster than 100 millisec. So I am setting up a QS138 V3 build [anchored to the walls and floor] to determine how much impulse ( Force X time = change in momentum ) the set-up can generated in 0.1 sec. The set-up employs a Fardriver 95560 controller, 5 x LiPO 20Ah 6s (24 C max discharge rate), a CycleAnalyst, wheel speed detector, a 200 amp shunt w RO and a timing device. I think the black-box mystery in this set-up is the controller and not whether enough impulse can be achieved in 0.1 sec by motor/ batts system plus a true WOT operable controller. This controller may have some build-in safety routines against WOT throttle signal input. I feel this system can deliver any comparable ICE/Clutch needed impulse response within 0.1 sec? But who knows? Hence a test is in the makings.

The real unknown ideas are how much overshot/undershot the clutch/throttle signal generator system will need at start-up to get the desired response when the tire meets the rock.




You ask, “Does anyone have any ideas how you could approximate power consumption with only throttle input and RPM? “

Do you want this power data for making experimental tests or data for the Arduino module? Either way you will need some form of a shunt for amperage. Voltage is somewhat easier to measure. Power = amps x voltage. I have gotten some digital amperage RO devices off eBay. Below is a picture of the 200 amp shunt under the Gorilla tape and it’s RO meter I will employ for now:8552B78A-359F-4586-B112-5A0C2CD0CD6B.jpeg
 
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Speedmd,

Energy never adds say some 1600 joules across a slipping clutch plate. Momentum change calculations will produce accurate answers. There are no slipping clutch plates with this BLDC direct motor hook-up.

In electric motors the magnetic flux ϕ = L I is equivalent to momentum. L is inductance and I is current.

But from a Dino WOT test of sorts on the QS-3000 V3 today, the shunt read 45 amps x 101 volts = 4550 watts very quickly (.3 sec ?)which would be in the ballpark of 1600 joules / .3 seconds. The load on the BLDC motor was a rear wheel knubby tire 4.0 x 18 that went from 0 mph to some 70 mph in less than 1 sec.

In a run with a vey slow creeping start the amps needle got near 100 amps before the rear wheel reached full momentum. The second moment of inertia of the rear is far greater than what these MC flywheels have.

The controller will not simply feed increasing amps for motor starting if the rear wheel is held too firm with the rear brake. The ebike (no flywheel) with the front tire against a wall and the rear tire on firm dirt can easily and very quickly supply enough torque to break traction while sit close to being over the rear tire.

I likely still have some limiting performance constraints set up in both the CycleAnalyst and the Fardriver that will need removal to max performance for max impulse generation. I have tripped the150 amp breaker on some steep paved roads. Sensor activated timing would pinpoint achievable magnitudes for impulse rates.

As of now it appears that the motor and batteries are sufficient but a more wide open controller might get higher than needed impulse generation — more runs.
 
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@DingusMcGee That's awesome that you're putting it to the test. I'll be fascinated to see the results.
It could be well worthwhile to look at the pick-up off zero rpm, and also from say 2-300 RPM "idle" to shed light on the reason everyone has gone to an 'idle'.

I realised I'd left the friction plates out of the clutch basket mass, but I don't think it changes anything. They are thin aluminium donuts with very little mass. I think it reasonable to call the spinning inertia of the basket, driven gear and friction plates significantly less than the static inertia of the steel pressure plates, hub, spring, bolts, gears & shaft they attach to. So any inertia they provide will get absorbed just getting the rest of the clutch spinning. Also given the reduction between the motor and clutch, any force from the flywheel/motor is multiplied compared to that from the clutch itself.

I figured it was going to be purely wild assumption to guestimate power from just throttle and RPM, but hoped there might be some vaguely valid assumptions that could be made. Possibly if I build a CAN version I can get appropriate figures from the controller, but that's a long way down the road.

The human speed component of clutch control fascinates me. It blows me out how fast and subtle the pro's must be to get the actions they do. I suspect your 100ms might be on the slow side.
Lab button pressing experiments give tremor speeds of 8-12/sec, right around 100ms. But that's full cycle operations, clutch control is a half-cycle action and also operating on a pre-loaded finger - a relaxation of muscle tension provides control input (as well as contraction going the other way). And we're looking at people who are highly trained experts at this specific action and who are utilising prediction based on many thousands of hours of training this specific control.
Where that leaves us I've really no idea, but I suspect that if a pro level rider was given a clutch that responded at 100ms rates they'd tell you it was broken. My wild guess is that they might discriminate down to 1/4 of that even if they can't actually control at that rate. Just guessing in the dark though.

Addendum: After writing below it occurred to me that the balancing aspect probably has some relevance to the response time question. Is 100ms fast enough to explain maintaining static balance on one wheel? I don't know the answer but it feels maybe a little slow to me? I guess there's a difference between discriminating input and controlling output too. Hmmmm.

@thepronghorn Also consider this scenario. You're slipping the clutch to balance on the rear wheel. Now you want to jump across to the next rock. On an ICE bike you raise the RPM while maintaining the clutch slip to balance, then when there's enough energy (RPM) you ease in the clutch a tiny bit to let the front drop. When the front has dropped enough (but still up in the air), you release the clutch to drive the back wheel across the gap, standing the bike back up in the process so it can land on the back wheel.
The question is how do you increase the power setting on the throttle without having to decrease the power setting on the clutch simultaneously? That's going to be crazy hard to coordinate while balanced on one wheel and possibly giving tiny little hops to keep lateral balance. A friction clutch basically doesn't change delivered power as RPM varies, so it doesn't really matter if the throttle is bopping all over the place as long as your clutch finger is steady.
Not impossible to develop an algorithm that might do it, but starting to get pretty complicated it seems to me, probably requiring some external sensors. Lots of development to do there before it's close to ready for prime-time.
 
A trials flywheel is more like 4-5000J than 1600.
0.3 seconds is not a useful time frame.
I spend a fair bit of time analysing 60fps video for trials training. You can discern transition from slipping to engaged clutch (from rear wheel movement) in 3-5 frames even from intermediate level riders with stock clutches.
Pro's setup their clutches so they are light switches compared to stock clutches. Even good riders can't get on a real pro level rider's bike and manage to use the clutch as much more than an on/off switch. But the pros finesse them beautifully.

Great to see some results from your testing @DingusMcGee. Go at it!
 
...................

@thepronghorn Also consider this scenario. You're slipping the clutch to balance on the rear wheel. Now you want to jump across to the next rock. On an ICE bike you raise the RPM while maintaining the clutch slip to balance, then when there's enough energy (RPM) you ease in the clutch a tiny bit to let the front drop. When the front has dropped enough (but still up in the air), you release the clutch to drive the back wheel across the gap, standing the bike back up in the process so it can land on the back wheel.
The question is how do you increase the power setting on the throttle without having to decrease the power setting on the clutch simultaneously? That's going to be crazy hard to coordinate while balanced on one wheel and possibly giving tiny little hops to keep lateral balance. A friction clutch basically doesn't change delivered power as RPM varies, so it doesn't really matter if the throttle is bopping all over the place as long as your clutch finger is steady.
Not impossible to develop an algorithm that might do it, but starting to get pretty complicated it seems to me, probably requiring some external sensors. Lots of development to do there before it's close to ready for prime-time.
I'm pretty sure I understand how clutches work. The clutch lever gives you control over the torque that the clutch is transferring from the flywheel + engine/motor to the rear wheel. With a physical clutch, it does this by controlling the pressure that squeezes the plates in the clutch together. With a virtual clutch, it could directly control the torque output of an electric motor since electric motors can be controlled very quickly (probably not as fast as clutches, or at least not with the controllers we normally use). The virtual clutch could also be programmed to only have the energy available in it that a flywheel would have (of course more energy can be added to the flywheel with the twist throttle).

I understand that mechanical flywheels and clutches are very well optimized to storing energy and sending precise amounts of it at precise torques to the rear wheel. I just wonder if a high torque motor with a highly responsive motor controller has been tried with a virtual flywheel setup like I outlined.

I've little interest in getting rid of a physical flywheel and a decent friction clutch, they just work so well. I am interested in seeing if electronics could effectively make that physical flywheel response adjustable.

I was going to ask this elsewhere, and probably will.
Does anyone have any ideas how you could approximate power consumption with only throttle input and RPM?
I don't need it to be accurate, I'm just thinking some figure that varies somewhat proportionally to real motor output. The number itself doesn't matter as long as I could apply a factor (experimentally field derived) that made that number useful to modify the slope of the RPM decay rate according to throttle position.
I'm considering the situation when you release the clutch with a progressively closing throttle - the decay rate slope will get steeper as throttle closes and motor power drops.
It's kind of icing on the cake, not so important for initial experiments.
Which part of the flywheel response do you want to adjust? You have a QS138 motor attached to a flywheel with a mechanical clutch. Seems like that should work great. What don't you like about it? Does your bike's motor controller not interpret your throttle position as a torque command? Maybe you want the throttle to be more like a flywheel speed controller with the clutch lever to modulate the torque output?
 
1600 joules hooked up in .1 seconds is 16KW going by the calculators I ran this am. The QS 138 is roughly 5kw without adding additional mechanical flywheel? 1600 is just for the added 800gram ring style flywheel. ICE setups are more than 800 grams when including the added mass in the crank. Agree with pete that the .3 second estimate is most likely a bit too long for the bigger moves. Also we would never use all the energy in the flywheel. 60-80% possibly? At least we have some numbers to work from.
 
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Does anyone have any ideas how you could approximate power consumption with only throttle input and RPM?
For a guesstimate of motor power, you'd have to assume a current-controlling throttle, so an FOC controller. Then you'd have to know what phase current (more specifically, the common current, variable name I can't remember but it might be Iq?) would be demanded by a specific throttle amount. Then you have to know the voltage.

With those two you can multiply to guesstimate watts.
 
I'm pretty sure I understand how clutches work. The clutch lever gives you control over the torque that the clutch is transferring from the flywheel + engine/motor to the rear wheel. With a physical clutch, it does this by controlling the pressure that squeezes the plates in the clutch together. With a virtual clutch, it could directly control the torque output of an electric motor since electric motors can be controlled very quickly (probably not as fast as clutches, or at least not with the controllers we normally use). The virtual clutch could also be programmed to only have the energy available in it that a flywheel would have (of course more energy can be added to the flywheel with the twist throttle).

I understand that mechanical flywheels and clutches are very well optimized to storing energy and sending precise amounts of it at precise torques to the rear wheel. I just wonder if a high torque motor with a highly responsive motor controller has been tried with a virtual flywheel setup like I outlined.


Which part of the flywheel response do you want to adjust? You have a QS138 motor attached to a flywheel with a mechanical clutch. Seems like that should work great. What don't you like about it? Does your bike's motor controller not interpret your throttle position as a torque command? Maybe you want the throttle to be more like a flywheel speed controller with the clutch lever to modulate the torque output?
I think you're probably talking something much like I'm trying to prototype but without the physical clutch at all?

So to solve the zero throttle but high available power you'd have an algorithm that basically timed how long and how far the throttle was opened. That sets the "available power" which would decay at some rate. You'd need an audio generator to give the rider feedback on how much power is sitting there untapped (I saw some research today that showed that people can respond to audio feedback faster than they can visual feedback).

I get confuddled when I try to imagine how the variable relationship between RPM, torque, throttle position & clutch position interact.
When riding on throttle you want a relatively slow & response (trials throttle response is stupid slow compared to an MX bike for instance), but on clutch you need instant response finely controlled. So the controller has to be capable of running two response profiles. Which I'm working on with my Arduino project.
I keep running into Wotif's like how do you address clutch changes simultaneously with throttle changes? Not impossible, but certainly takes some thinking about. Or how do you deal with instant power cut - with a clutch the only rotating mass connected to the wheel is the clutch and gears which have very low inertia and have a low gear differential to wheel speed. If you dispose of the clutch then the motor rotor is connected into the system and it has some significant inertia and has a high gear differential to the rear wheel (unless you use a very slow revving high torque motor, in which case the diameter usually increases so the MoI increases and how far ahead have you really gone? I don't know the answer to that question, just putting it out there.)
Stopping a bike or cutting power virtually instantly is just as critical as accelerating it. Even the best riders typically top out on steps with excess power and control it by pulling the clutch for virtually instant power cut, the back wheel is now free to stop or even rotate backwards with very little inertia to fight. You've got to be a magician to get to the top of a step with exactly zero surplus power available.

I can see it might possibly work, but I always end up back thinking that it's got an awful lot of complications to overcome.

As far as my current bike goes, what I don't like are:
  • The clutch itself is nowhere near nice enough for really fine, accurate control. It's a coil sprung unit - all modern trials bikes (except Beta) use diaphragm springs because they feel so much better. That's got nothing to do with the electrics, but it's a problem. Feel is very hard to quantify, but it's extremely important - if you can't feel what's going on you can't respond.
  • The gearing is too fast. It can do about 45-50kmh on it's current single gear. That's so unbelievably frustrating when you eg want to snap up onto an obstacle that's maybe a foot or less in front of your front wheel from balanced stationary. By the time you've got enough energy in the system to get the pop needed then the back wheel accelerates to too high a top speed and hits the face much too hard, so it bounces. It also makes the overall action from go to woah too fast. With a lower gear the initial pop is slightly faster but the last 1/2 - 3/4 of the action (flight & landing) is slower, so the overall time is longer which gives more opportunity to react and respond. Maybe electronic control could avoid this, but then you need an even bigger motor to generate the torque - vicious circle. 2-speed gearbox hopefully arriving in next few weeks.
  • When ridden without clutch it's woefully slow to respond (as are ICE bikes, that's just the problem with riding on throttle). You have to start movements so far in advance of when you need them, it's like always having to anticipate two steps ahead, never actually here-&-now. And then there are many movements that are simply out-of-bounds. And that's with a throttle that is definitely on the quick side of things.
It's got a Fardiver running torque mode. I slightly preferred the Nucular with Torque+Speed mode, but my Nuc is only 12F so underpowered, and it can't idle properly.
Trying to coordinate clutch and a non-idling motor is way, way too complicated - it completely does your head in. Touch the throttle before you've got the clutch in and you lurch forward. Or if you've got the clutch in too far then you get a motor that spins up quickly, but then you've got to flick out some clutch to find the engagement point before you lose balance - and oops too much and you lurch forward. Clutch not far enough in when you touch the throttle and guess what? Lurch forward. Horrible!

All this is why I've come to thinking that a hybrid system might be achievable and provide some good insights to go forward from. The Virtual Flywheel should make the physical flywheel 'tuneable'. Slippery conditions? Dial down the flywheel acceleration to smooth out the power. Dry granite? Dial up flywheel acceleration and dial down deceleration so you can spin it up fast then smash power down onto that grippy surface.
All while keeping the light switch power off, separation of available and applied power, insensitivity to throttle variation etc.
Seems like a feasible and possibly useful step forward.
 
For a guesstimate of motor power, you'd have to assume a current-controlling throttle, so an FOC controller. Then you'd have to know what phase current (more specifically, the common current, variable name I can't remember but it might be Iq?) would be demanded by a specific throttle amount. Then you have to know the voltage.

With those two you can multiply to guesstimate watts.
Cheers.
I guessed that I could assume current controlling throttle (controller eg Fardiver or Nuc in current mode). Phase current I was thinking I could derive a VERY rough approximation simply by looking at figures out of my Nuc - I expect that will have a pretty huge fudge factor because I expect the current varies considerably according to load (?). But I don't really care if it's not accurate, I just want to investigate what effect it can drive.
It's the Voltage that I have no clue. That's either a total guess or some bit of math around all the Lq, Gv, Pq Bs .... figures that are completely Latin to me! Or perhaps you can measure it directly off the motor terminals? I've no idea. And I'd prefer to just guess than have to work out more inputs to the controller - that's going to be my weakest point.

Maybe I just pick a totally arbitrary curve and play with it?
 
This is what we need to get real the world picture of what happens.
RWT-MX Rear Wheel Motocross torque transducer.

Bolt-on adapter between rear wheel & sprocket with inductive power, wireless output ...
Surely they must be common as muck and cheap as chips. :ROFLMAO::ROFLMAO::ROFLMAO:

Couldn't be too hard to make - just a lump of aluminium and a strain gauge - simple. 🙃😂🤩
 
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Cheers.
I guessed that I could assume current controlling throttle (controller eg Fardiver or Nuc in current mode). Phase current I was thinking I could derive a VERY rough approximation simply by looking at figures out of my Nuc - I expect that will have a pretty huge fudge factor because I expect the current varies considerably according to load (?). But I don't really care if it's not accurate, I just want to investigate what effect it can drive.
It's the Voltage that I have no clue. That's either a total guess or some bit of math around all the Lq, Gv, Pq Bs .... figures that are completely Latin to me! Or perhaps you can measure it directly off the motor terminals? I've no idea. And I'd prefer to just guess than have to work out more inputs to the controller - that's going to be my weakest point.

Maybe I just pick a totally arbitrary curve and play with it?
If you only need to know the ballpark power, then you can use the battery-to-controller current (which means you can also use battery voltage at the same instant).

It doesn't give you *motor* power, but it's "easy".
 
Just a deviation. Here's a short clip of the EM Factor-e's first public appearance.
Gael came last in this event, but this is possibly the first time I've seen an e-trials do a convincing rendition of a "stuff" or static punch. Around 25s mark. And again at the next sloping step.
That's the acid test of the fast end of the clutch pop spectrum to me.
I've never seen a good clean lift like that one from an electric trials before. My bike with it's oversize flywheel does them pretty well, but the rider lets it down badly :)
 
If you only need to know the ballpark power, then you can use the battery-to-controller current (which means you can also use battery voltage at the same instant).

It doesn't give you *motor* power, but it's "easy".
That sounds doable and clarifies what Dingus was probably suggesting.
Looks like in order to catch the peaks the wheel sprocket power meter needs to have a bit more head room than what is spec'd.
"(Higher Torque on Request)"
You pay your money you get your device.
Except I'll guarantee it's out of my budget unless one turns up on Marketplace in a deceased estate job lot!

I've often wondered about the practicality of building a chain deflection tensiometer - that's a relatively simple device that can give decent results. But I suspect that trying to get sensible data out of a motorcycle chain bumping about on dirt & rocks might be a signal processing nightmare.
First build something that can deal with the surface roughness of a multi-link chain, then deal with all the extraneous signal as that bounces about.
The second part could be simplified by using a pretty high deflection force value, perhaps with a mechanical 'floor' so the chain mass becomes fairly insignificant. It would only start to read when tension rose high enough to lift the chain off the 'floor', but that's probably acceptable for big picture stuff.
But the form of the chain would inevitably introduce a heap of noise to try to deal with, which could be quite hard given we're not talking a constant frequency. Perhaps using a quite large sprocket as the pressure point could smooth things out adequately to get useful data.
I keep throwing it back in the too hard basket.
Any Uni students need a DAQ/metrology project?
 
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I took some video of various stationary punch technique today with the camera setup so I could watch clutch lever, chain and rear tyre.
Interesting!
Elapsed time for clutch release was around 0.05 to 0.08s. A bit faster than I expected really.
It's hard to tell, but I'd guess that the wheel reaches full rotational speed only a tiny bit slower than the clutch release, if at all. I'd call it 0.06 - 0.1s.
I haven't calculated the RPM (I can count engine firings and time it against the video timecode to get a reasonable approximation, but it's a bit of mucking around so haven't bothered. Gut feeling is that I had the bike at around 3 - 4,000 RPM on an average attempt.

So we're looking at driving a motor to 3,000 rpm in a good bit under 0.1 seconds, assuming the motor is capable of max rpm around 9,000. Scale to suit.
Remember, this is with the motor driving a wheel under high load, not sitting in the air. The best video I got was from starting with the front of the bash guard sitting up on a log, so the bike had to drive the guard forward and up the log in order to accelerate, from a total standstill. The wheel rotated about 90 degrees before it had impacted the log and bounced into the air as we climbed up and over.

I'm a capable intermediate/upper intermediate sort of rider. I've got my clutch lever set far inboard so my finger is further toward the end of the lever to increase the range of movement for better fine control (compensate for my lack of skill). I run an oil that I find has very nice smooth engagement.
Pros run their clutch levers right out near the grip so their finger is as close to the pivot as they can get them for fast response. They use far heavier clutch springs and mostly faster grabbing oils. They've got the skill & finger strength to have excellent fine control with that setup. If I rode those bikes it would be a comedy show as I flicked the switch on and off. I know a good rider who has ridden a Trial GP pro bike while minding - he said he virtually gave up trying to use the clutch and just accepted it was all or nothing.
So the Pros would be significantly faster on the clutch - no doubt at all. You're probably talking under 0.05s to get the motor fully spun up under significant load. They will release the clutch while the front brake is still locked and the tyre pressed hard into a vertical face. The brake comes off as, or infinitesimally after, the clutch starts to engage. Wicked control and timing! And pretty solid resistance for the motor build RPM against.
The first 10-15 degrees of wheel rotation is driving the swingarm up under the bike, squashing the tyre into the ground. Then the bike starts to really move.
Now to keep it in perspective, the pros except the very pointy end, a handful of riders, use stock standard bikes with just their own rear shock & their favourite clutch pack put on them. Plus personal grips, pegs etc. But the bikes are generally bog standard except those few parts. So my bike is not too far from what the pros ride.

We've been largely talking torque, but keep in mind the goal is to turn the wheel, so RPM is critical too. That loaded wheel rotated the 90 degrees or so in about 0.13s

Now where's that torque transducer? :)
 
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