The ultimate torque arm (For <2kW and standard axles)?

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 16, 2018 7:53 am

Alan B wrote:
Apr 15, 2018 10:41 pm
We have seen thick solid chrome moly steel dropouts with no relief slots spread by 12mm hubmotor recoil when they were slightly less than fully seated. I think this is a somewhat similar "force multiplier" to the slots in this proposed design.
Once again, the difference is between trying to deaccelerate the sharp edges of those flats once they are already moving, using brute force and an immovable object; and preventing the shaft from accelerating in the first place, by the application of engineering in the guise of the well-documented and tested science behind
  1. shock absorption using spring steel;
  2. damping via friction.
It looks like this:
TA3-3d.jpg
TA3-3d.jpg (22.9 KiB) Viewed 233 times
Those green lines show the maximum strain (stretch) the springs need to accommodate, 0.5mm before the axle will be arrested from rotating further by the standard dropouts.

The torque is acting 7.5mm(right) & 5mm(left) away from the centres of rotation (the middle of the holes at the end of the slots), and is restrained by the minimum cross-sectional area of 24.9mm²at an angle of 15.82° below horizontal both sides.

The inner 1/3rd of that area is in tension, the outer 2/3rds in compression. The maximum extension (stretch) is 0.4% the maximum compression 0.23%.

The material specified is C70 spring steel, hardened to 60HRC and then tempered back at 260°C ('red brown') to 50HRC yeilding a tensile strength of 1.663GPa.


That's all the information required to do the calculations, and all the formulae required are available here for anyone who can be bothered to do the math.

As the axle starts to twist, the nearly 50mm² (minimum; and in actuality much more as the bottom of the C also shares the burden) of spring steel acts to resist it(resiliently). The wings will be forced apart a little -- they are designed to do so -- but before the axle makes contact with the dropout faces -- if it ever does -- the initial torque impulse will have been absorbed by the springs, and that energy dissipated through the friction between the layers, and between the layers and the constraining frame & nut.

The bike's mass will start to roll forward, the springs will press back against the axle tending to return it to its centralised position. The shock load is contained and the energy dissipated. Job done.

When you hit the brakes, assuming a DD hub, bemf kicks in and everything reverses. The symmetry of the C shape means it works just the same in reverse, except now with the higher leverage acting anticlockwise at the top of the left wing, the arm of the TA also comes into play providing a slightly stiffer spring rate under braking.

Yes, it still needs to be tested -- and I will when I can -- but mostly to ensure that I have done sufficient to lower the spring rate -- by reducing the section with the slot -- to ensure that it absorbs rather than transmits the force (as a solid TA would do).

It might be too stiff, but nothing is going to break, given 24.9mm² * 2 sides * 1.663 GPa (1000Newtons/mm²) tensile strength, the thinnest section (alone) is capable of withstanding 82,817.4N of force.

I'm done now. When I've made some, maybe I'll come back.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by amberwolf » Apr 16, 2018 3:55 pm

Buk___ wrote:
Apr 16, 2018 4:19 am

Even stranger that you would come along and make such a song & dance about such an off topic point so long after the fact.
Im pretty strange, and I dont think like other people. Sometimes I latch onto something and until I resolve it I cant really get past it. :/

Sometmies thats helpful, and sometimes its just annoying. Sometiems it pisses people off, so I do as much as I can to avoid it, but when Im really confused about it I have a super hard time letting it go till its resolved.

All that said, Im still following this idea, and if I had the ability to make and test these Id do it just to see how well it works. If I am understanding it correctly, it ought to work for the typical ebike power levels, and probably even up to the power levels Im using on SB Cruiser, since its split between the two motors, though itd be pushing towards the upper end of the topical intent of these.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 16, 2018 6:36 pm

amberwolf wrote:
Apr 16, 2018 3:55 pm
If I am understanding it correctly, it ought to work for the typical ebike power levels, and probably even up to the power levels Im using on SB Cruiser, since its split between the two motors, though itd be pushing towards the upper end of the topical intent of these.
Not even close. With 2 pairs and if you increased to say 10mm/20 layers per side, it would probably handle the torque of drive. Maybe.

But with (from memory) 400+lbs of bike weight -- I can't remember if that was with or without you and the dogs -- and the ability to load another few hundred pounds of dog food on the back, the transition from a rolling (say) 10mph, to regen would be vicious.

With all that weigth act via 20"? wheel rolling forward, and your motors slamming into regen, the torque at the dropouts would be far more than even 40mm of spring could absorb/shed in the required time frame. The effect would be as if they weren't there.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by amberwolf » Apr 16, 2018 6:46 pm

Oh. :( (this is why I often tell people that me and math dont get along...because I think I do it right and then find out I made some serious mistake).

But thats ok, youre not designing these for stuff like mine. ;)

400lbs+ is with me on there, without any dogs or cargo. Figured it was over half a ton with the trailer and cargo area full of dog food last year. :oops:

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Alan B » Apr 16, 2018 8:33 pm

Buk___ wrote:
Apr 16, 2018 6:36 pm
amberwolf wrote:
Apr 16, 2018 3:55 pm
If I am understanding it correctly, it ought to work for the typical ebike power levels, and probably even up to the power levels Im using on SB Cruiser, since its split between the two motors, though itd be pushing towards the upper end of the topical intent of these.
Not even close. With 2 pairs and if you increased to say 10mm/20 layers per side, it would probably handle the torque of drive. Maybe.

But with (from memory) 400+lbs of bike weight -- I can't remember if that was with or without you and the dogs -- and the ability to load another few hundred pounds of dog food on the back, the transition from a rolling (say) 10mph, to regen would be vicious.

With all that weigth act via 20"? wheel rolling forward, and your motors slamming into regen, the torque at the dropouts would be far more than even 40mm of spring could absorb/shed in the required time frame. The effect would be as if they weren't there.
This response puzzles me. The torque reaction of the motor on the torque arm via the axle flats is from motor torque reaction, and will be limited to that which the motor can magnetically produce. Vehicle weight doesn't enter into it.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Chalo » Apr 16, 2018 11:37 pm

Alan B wrote:
Apr 16, 2018 8:33 pm
The torque reaction of the motor on the torque arm via the axle flats is from motor torque reaction, and will be limited to that which the motor can magnetically produce. Vehicle weight doesn't enter into it.
It matters to the degree that inertia, weight, and surface adhesion are the forces that the motor reacts torque against. No matter how powerful the motor is, it can't transmit more torque than it can stick to the ground.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Alan B » Apr 16, 2018 11:40 pm

Chalo wrote:
Apr 16, 2018 11:37 pm
Alan B wrote:
Apr 16, 2018 8:33 pm
The torque reaction of the motor on the torque arm via the axle flats is from motor torque reaction, and will be limited to that which the motor can magnetically produce. Vehicle weight doesn't enter into it.
It matters to the degree that inertia, weight, and surface adhesion are the forces that the motor reacts torque against. No matter how powerful the motor is, it can't transmit more torque than it can stick to the ground.
We're not burning rubber with a heavy bike and a 2kw hubmotor. That would only reduce the torque load, not increase it anyway.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by MadRhino » Apr 16, 2018 11:49 pm

Chalo wrote:
Apr 16, 2018 11:37 pm
...No matter how powerful the motor is, it can't transmit more torque than it can stick to the ground.
Well, torque does kick, even on a wheel that doesn’t touch the ground.

When I give it some throttle whilst in a jump, my motor does lift the front of my bike. If I give too much, it can back flip my bike and myself in a second. Of course, inertia is only a fraction of the resistance of traction, but it is still a significant force. A motor wheel on a bench, that we power and regen back and forth, will eventually destroy its dropout or axle.
Make it fool-proof, and I will make a better fool.
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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 17, 2018 12:03 am

Alan B wrote:
Apr 16, 2018 8:33 pm
Buk___ wrote:
Apr 16, 2018 6:36 pm
amberwolf wrote:
Apr 16, 2018 3:55 pm
If I am understanding it correctly, it ought to work for the typical ebike power levels, and probably even up to the power levels Im using on SB Cruiser, since its split between the two motors, though itd be pushing towards the upper end of the topical intent of these.
Not even close. With 2 pairs and if you increased to say 10mm/20 layers per side, it would probably handle the torque of drive. Maybe.

But with (from memory) 400+lbs of bike weight -- I can't remember if that was with or without you and the dogs -- and the ability to load another few hundred pounds of dog food on the back, the transition from a rolling (say) 10mph, to regen would be vicious.

With all that weigth act via 20"? wheel rolling forward, and your motors slamming into regen, the torque at the dropouts would be far more than even 40mm of spring could absorb/shed in the required time frame. The effect would be as if they weren't there.
This response puzzles me. The torque reaction of the motor on the torque arm via the axle flats is from motor torque reaction, and will be limited to that which the motor can magnetically produce. Vehicle weight doesn't enter into it.
The heavier the bike, the more torquey motor needed to accelerate it at a reasonable rate.

So presumably you won't argue that the more torquey the motor, the greater the (negative) torque reaction it will produce at the axle when it snaps into regen.

Doesn't even require math; just a little common sense.

Now I guess it possible that AW's machine accelerates like a slug and deaccelerates at a similar low rate when using just regen; but if it has enough power to get 1/2 a ton of bike, people, dogs and goods moving up grades, then the snap into regen is more than I would consider comfortable asking the spring TA to deal with.

(Don't you tire of your Devil's Advocate role?)

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 17, 2018 12:24 am

Alan B wrote:
Apr 16, 2018 8:33 pm
Buk___ wrote:
Apr 16, 2018 6:36 pm
amberwolf wrote:
Apr 16, 2018 3:55 pm
If I am understanding it correctly, it ought to work for the typical ebike power levels, and probably even up to the power levels Im using on SB Cruiser, since its split between the two motors, though itd be pushing towards the upper end of the topical intent of these.
Not even close. With 2 pairs and if you increased to say 10mm/20 layers per side, it would probably handle the torque of drive. Maybe.

But with (from memory) 400+lbs of bike weight -- I can't remember if that was with or without you and the dogs -- and the ability to load another few hundred pounds of dog food on the back, the transition from a rolling (say) 10mph, to regen would be vicious.

With all that weigth act via 20"? wheel rolling forward, and your motors slamming into regen, the torque at the dropouts would be far more than even 40mm of spring could absorb/shed in the required time frame. The effect would be as if they weren't there.
This response puzzles me. The torque reaction of the motor on the torque arm via the axle flats is from motor torque reaction, and will be limited to that which the motor can magnetically produce. Vehicle weight doesn't enter into it.
Having read my first response back, and then re-read your post, I'm guessing it won't satisfy you because of my "driving maybe, braking no".

Whilst the torque at the axle is limited in both directions to what the motor can create, when driving, it is also limited by whatever AW's batteries, controller, wiring et al. can deliver in terms of amps. And if his setup is like most (from what I read here) DD setups, the motors are probably capable of producing significantly more torque if he supplied enough amps.

If that is true, then in regen, the motor may well produce significantly more torque than it does with his drive power envelope. What happens if the motor produces more amps than the controller can handle I'm not exactly sure -- not my field.

Some will get dumped as heat in the FETs; some will produce heat in the windings and cables, some will generate heat in the battery pack itself; but all of that is upstream from the coils cutting the force lines from the magnets, and that what produces the torque reaction at the axle.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Alan B » Apr 17, 2018 1:10 am

As long as the traction is not broken (Chalo's point), the torque is a function of the motor and the current. Not of the system weight.

Amber's setup doesn't use particularly powerful motors as I understand it (but I haven't been keeping up with his latest projects), just that it has two, but each has it's own torque arms. Doubling the power does make a difference, and I expect the acceleration of his loaded system is considerably less than we are accustomed to on our light ebikes.

The motor's capability to convert current to torque and back is not really different (the magnetics and copper limits are the same), in the case of regen the mechanism used to raise the voltage to battery voltage reduces it further. If you dead short the motor you might get more current than you send it because the system resistance has been reduced, but this is only done for a fraction of the time with regen, so the average current is not that high. In practice I don't think I've seen much more than about half the power on regen that I've seen on max acceleration. I haven't paid too much attention to it as with high regen the speed drops quickly as does the power, so the peak is fairly brief. Max power on regen is at max speed, to get full battery voltage would require downhill that was sufficient to get to unloaded wheel speed. At normal speeds the motor produces lower than battery voltage, so the power/current is lower also. At 10mph the voltage is 1/2, and the peak regen power is about 1/4 of full with a 20 mph system.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 17, 2018 1:45 am

Alan B wrote:
Apr 17, 2018 1:10 am
As long as the traction is not broken (Chalo's point), the torque is a function of the motor and the current. Not of the system weight.
...
Max power on regen is at max speed, to get full battery voltage would require downhill that was sufficient to get to unloaded wheel speed. At normal speeds the motor produces lower than battery voltage, so the power/current is lower also. At 10mph the voltage is 1/2, and the peak regen power is about 1/4 of full with a 20 mph system.
Peak power may be a function of angular momentum, but how long it is sustained is a function of mass.

All of which is another nice irrelevant distraction from the subject of the thread.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by fechter » Apr 17, 2018 12:31 pm

Right. It only takes a millisecond to make the TA fail. As long as it can withstand the peak force, the duration of the force is irrelevant.
In practice, most regen systems apply less torque than the drive but I would design for an equal torque.
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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by amberwolf » Apr 18, 2018 4:05 am

Apologies for derailing the thread...it wasnt my intention. :(



For those that want the OT info below, Ive just shrunk it to keep the OT to a minimum. :/
Alan B wrote:
Apr 17, 2018 1:10 am
v
Amber's setup doesn't use particularly powerful motors as I understand it, just that it has two, but each has it's own torque arms. Doubling the power does make a difference, and I expect the acceleration of his loaded system is considerably less than we are accustomed to on our light ebikes.

If it helps, they are each the MXUS 45H, a 4503 and a 4504.

The left one is driven by a generic 15FET with modded shunt (added one extra shunt in parallel) that gets up to at least 50-60A peak battery current (cant remember exactly; I thought it was around 100A but cant find the data right now) during acceleration. The right one is driven by an old unmodified Grinfineon 12FET with 40A battery current limit. Something like 4-4.5Kw peak during acceleration, IIRC.

Unloaded except for me, so perhaps a bit less than 1/4 ton (wierd to think of it that way :oops:) acceleration is just over 3 seconds from 0-20MPH with a fresh charge, and for the first few Ah / miles.

Deceleration from 20MPH to zero is a little quicker than that; sorry I dont remember the exact time. Maybe half? (leftside uses EABS to actively brake the wheel using power from the battery, rightside uses regen feeding power to the battery, which nearly cancel each other out (little extra regen current), so braking tends to remain about the same overall regardless of battery SoC). Dont know what the current on each side is, as both brake enables are tied together and I havent got separate shunts for each controller, so I dont know what the peak braking power actually is.

Theres about 6 - 8A regen current that makes it back thru teh shunts; the rest of the regen presumably is siphoned off straight from the Grinfineon to the generic, never having to go thru the rest of the battery wiring, shunts, or cells. (if I ever get to beefing up the wiring from one controller to the other, I wonder if itd increase braking any?)

Battery is 14s2p EIG NMC (c020 cell, IIRC), 52v 40Ah nominal, mid-30s milliohm pack resistance according to the CAv3.1, depending on SoC. IIRC, wiring from pack to parallel pair of Grin 45mohm shunts (just prior to controllers) is something like 3 feet or so of 8g wire on each side (+ and -) with a breaker and a battery cutoff in the + line.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Alan B » Apr 18, 2018 9:12 am

Continuous Torque is limited by the magnetics.

Peak torque can be greater from hammering if the stator is allowed to accelerate due to lack of adequate torque reaction restraint, which is generally a more significant problem when changing the sign of the torque as occurs in systems cycling between regen and acceleration. The stator's rotational acceleration is damped by the friction from tight axle nuts and constrained by the free play and stiffness of the torque arm system. If the axle nuts become loose the hammering torque will increase substantially.

The hammering is a function of the stator's rotational mass, average torque, rotational movement angle and friction, but not the bike's total mass.

It is critical to keep axle nuts torqued properly to provide the friction term and control the peak torque from hammering. Some axles are butter soft steel, it becomes difficult to keep correct torque without excessive torque which will fail the axle and/or nut threads. Whether it be from too much clearance, or too much spring in the torque retention system, movement leads to one nut getting loose and reducing the necessary friction, and the other nut becoming too tight which doesn't increase friction much but does threaten to ruin the axle and/or the nut threads. Justin measured the effects of nut tension on the failure torques of torque arms. Moderate nut tension was a significant factor in making torque arms more effective. Higher nut torque didn't help much, but lower nut torque reduced the recoil torque required to fail the torque arm significantly. These were continuous torque tests so did not take into account the hammering effects. Nut torque generates friction that is important in several ways.

With cyclic motion from torque sign changes the axle nuts tend to loosen. Regular lockwashers are not effective at preventing loosening in this situation. Wired nuts, cotter keys or wedge locking washers must be used. Tight tolerances are important as well.

The slots and "C" shape in this design allow the spring steel to move a bit before it develops adequate resistance to stop the axle rotation. This motion can lead to loose nuts and several failure modes.

The most successful torque arm designs have had minimal clearances and very low spring coefficients, helping to keep the nuts tight, or had enough stiffness and lack of motion (zero clearance clamping types) that the nut friction is no longer required at all.

This is all interesting to think about, but the reality will not be known until tested. Even with the best engineers and simulations, rockets require testing, and things don't always go as planned.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by fechter » Apr 18, 2018 1:14 pm

Alan B wrote:
Apr 18, 2018 9:12 am

This is all interesting to think about, but the reality will not be known until tested. Even with the best engineers and simulations, rockets require testing, and things don't always go as planned.
rocket-explosion.jpg
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"One test is worth a thousand opinions"

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 18, 2018 4:27 pm

Alan B wrote:
Apr 18, 2018 9:12 am
...
Most everything you said in this post -- and you said a lot -- is wrong.

But as always with you, you 'state' your opinion, but do not
  • cite any references;
  • show any math, formulae or laws -- no numbers at all;
  • construct vector force or free body diagrams; not even a picture or two;
  • nor even offer any analogies;
by which those statements might be understood, analysed, much less verified or challenged.

So, for anyone to challenge your statements, they first have to try and extract the details of your premise, construct a logical argument from them -- in numbers, pictures or analogy -- and then deconstruct it by challenge.

For those of us that have bothered, you have one of three responses:
  1. Repudiate one minor part of the reconstruction, and use that to deny the entire counter argument has any bearing upon what you had actually stated.
    .
  2. Pick out some irrelevant detail -- Nord-lock washer -- and ramble on and on and on and on about it ad nauseam to distract and confuse; whilst ignoring all the carefully and laboriously prepared counter-arguments debunking your statements.
    .
  3. And if you can find nothing trivially distracting or irrelevantly pedantic to pick at, you simply stop talking and bide your time until you do find it.
I don't know what your career is (or was), but as sure as eggs are eggs, you are not an engineer.

More a wordsmith; reasonably accomplished at putting together a few strings of technical sounding words, into plausible sounding sentences; and adding enough finality and definitivity, to be perceived by many as authoritative. Even I was fooled; for a while.

I have no doubt that you are capable of bolting together a bunch of pre-made parts and making something that works; and you've got enough front to claim it as some masterpiece of engineering; but assembly line workers do the same thing with 4 hours of on-the-job training.

I'm fully aware of the engineering process, I did it for the best part of 40 years. Testing is an important part; but that comes after gathering the requirements & constraints, limits and tolerances of the problem; analysing them and looking at both existing solutions and looking for innovations.

Then comes design, materials analysis, and the math. (The bits so totally absent from most every discussion here.)

Then comes peer review -- and that's where the subject of fechter's (somewhat distasteful) pictorial analogy fell down. (The report makes for interesting reading (for engineers at least). For the technically challenged there's a half descent summary here)

Once the peer review is done and any changes are fed back into the design, then -- and only then -- does it make sense to prototype and test.

But you're not an engineer; you're at best, a mechanic; at worst, [redacted]. You buy (from what I've seen expensive) components -- presumably on the basis that if it costs enough it'll probably do the job -- bolt them together and try it. If it doesn't break, you count it a success and proclaim your prowess.

I came here looking for three things:
  • to get some education on the electronic (controller) aspects of ebikes.
    There are undoubtedly those here who could help me, but they aren't sharing.
  • Some clarifications on the magnetic operations of motors.
    But on the basis of what I've seen here, this place collectively, has less understanding of this than I already do; and harbours some very strange and indefensible -- in the rigour of physics and maths -- ideas and myths.
  • for peer review of my mechanical design.
    But for that you need peers.
Once I've worked through the design mathematics -- having brushed up on a bunch of stuff I haven't needed since college -- I might just take the time to come back and debunk that steaming pile you wrote to which I'm responding; blow-by-blow; but for now I've got my plate full having made contact with some real engineers who are helping me work out the kinks in the design of this, and a few other 'bits & bob's.

For now, in common with a few other trolls, pedants, bodge artists and fakirs, *you're going on my ignore list so I won't see -- and thus be tempted to debunk -- the [redacted] you post.

*Except I can't, because you're an administrator. Which probably explains one or two other recent mysteries.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Alan B » Apr 18, 2018 8:06 pm

Stooping to personal attacks? Wow. I expected better.

Well, you are wrong again. On so many counts.

Eventually you'll figure it all out.

Good luck.

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Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 18, 2018 9:15 pm

amberwolf wrote:
Apr 18, 2018 4:05 am
Apologies for derailing the thread...it wasnt my intention. :(
You didn't!

amberwolf wrote:
Apr 18, 2018 4:05 am

If it helps, they are each the MXUS 45H, a 4503 and a 4504. {snip:details}
Some math based on those details.

Mass: 1/4 ton (225 kg).
Speed: 20mph (32kph, 8.89m/s);
Time: 3 seconds.

Acceleration: 8.89 / 3 = 2.963 m/s²
Distance covered: 0.5 * 2.963 * 3 * 3 = 13.33 m
Energy required: 0.5 * 225 * 8.89 * 8.89 = 8,892 J.
Power required: 8892 / 3 = 2964 J/s.
Electrical power assuming 85% efficiency = 3.487 kW.
At 52V nominal, it would require 67 Amps.
With freshly charges (to 4.15V/cell) 58.1V = 60 Amps.

Your EIG C020 are rated at 20Ah, and 5C continuous, 10C max. < 10s, so with 2P you could theoretically be drawing up to 400A for your acceleration, which clearly points to your controllers as the limiting factor.

On the flip side, winding current only matches battery draw when WOT; (100%PWM). At lesser settings, the winding current -- and thus the torque -- can be substantially higher than the battery/controller are capable of delivering.

When PWM<100%, as the voltage is being pulsed, the average winding voltage over time, is less than the battery voltage. But Vbattery * Ibattery needs to be equal to Vmotor * Imotor; as the Avg( Vmotor ) < Vbattery, Imotor has to be higher to compensate.

I seen this alluded to here, but never a simple, cogent explanation of why. Of course, it gets complicated once you start factoring in the inductance into the equation.(You'll see why I mention this later.)

To achieve an acceleration of 2.963 m/s², assuming a 220mm rolling radius.

225 * 2.963 = 666.675N
Acting at 0.22m, gives 146.67 N.m

Of course, in the real world acceleration won't be constant, so you're probably delivering substantially more than that at the early stages. As the rpm increase, the torque dies away, but the power builds.

I thought about trying to work back from the specs for your motors (Different model number, but the closest I found) to estimate the torque constant, but given two (and slightly different motors), different controllers, nothing by way of performance figures for the motors, and some hazily recollected data, I might just as well wet my finger and stick it in the air.
(Seems to be the done thing around here! :) )

That brings me to regen; and how much force the motor acting as a generator can feed back via the stator to the axle.

There are 3 methods of producing a deaccelerating force (braking) from a motor
(Eg. 36V system with a motor capable of generating 45 volts and a 1Ω internal resistance.)
  1. Disconnect the motor from the battery and short the windings and use the motor's own resistance to sink the voltage generated.
    Sometimes known as Dynamic braking; the generated voltage can also be shunted to a suitable external resistance.

    The power dissipated is:

    (45Vgen/1Ω)² * 1Ω = 2025W. (Effective braking)
  2. Feeding the generated voltage (BEMF, with its opposite polarity) back to the battery (+ve to +ve, -ve to -ve). (Charging regeneration.)

    This is what one of your motors is doing.

    Power dissipated (and hopefully, in large part captured) is:

    ((45Vgen - 36Vbat)/1Ω)² * 1Ω = 81W. (Gentle braking.)
  3. Using the the controler's bridges to feed the BEMF back to the battery +ve to -ve.

    This is what the other of your motors is doing.

    Power dissipated is:

    ((45Vgen + 36Vbat) / 1Ω)² * 1 = 6.561kW. (Hard braking.)

    This is only sustainable for short periods; but if you're getting to 0 from your max. (cruising?) speed in <3 seconds,
    then you'd be pushed to abuse it.
In reality, 1) and 2) coexist most of the time, with the Vgen flowing to the battery during the on pulse and back around the motor during the off phase, with the throttle controlling what percentage of which is happening at any time. Close the throttle for effective braking, but wasted energy, open it to put energy back into the battery, but only gentle braking.


I don't know if you recall one of our earlier conversations about regen; I was asking about the settings in my controller that talked about gentle/hard braking? I eventaully found the document with an explanation of the different forms regen can take, scanned it, but as my motor can't do regen, it was only of for the sake of knowing and I didn't expend any effort at that time to take it all in.

However, some of it stuck, because when Alan_B was getting uppity about why I was concerned about you trying my TA on the SBCruiser, I mentioned something about regen being capable of producing higher torque than driving the motor was capable of producing.

Of course, he poo-poo'd it.

(I envisage him as a General Melchett character, a reference you may not be familiar with, but this will give you a flavour and and this will explain the 'poo poo' :))

I'm writing this whilst waiting for the 3D FEA of my TA to run; but its a free account to an online service which means they severely limit the rate at which jobs can run.

Add to that the 12 x 0.5mm spring layers + frame and nut, and the 13 low-micron (surface irregularity) component interfaces which are an inherent frictional part of the design, and the mesh has to be very fine, so produces a huge number of tetrahedrons. It ran for 9 hours before telling me that it didn't like the way my CAD system structure the data, and ended in failure. :(

BTW. I have another novel design that addresses some of the issues raised and was prompted in part by your far greater energy and torque requirements detailed above:
AmberWolfTA.jpg
(86.23 KiB) Not downloaded yet
The two C-shaped parts are design to fit around the axle and then slot together, with the wedge shaped prongs on one, fitting into wedge-shaped slots in the other. As the nut is tightened, the wedge act to clamp the pair securely to the axle flats.

The arm -- not shown -- is another multi-layer edgewise cantilever beam affair, that is attached to the frame with a single, pivot screw.

The two slotted C-parts are fixed to the axle and then the swiveling spring arm clicks into the slot in the thicker C-part with a positive action that needs a small lever -- screwdriver, coin -- to release it.

In this way,
  • the axle is protected from impact damage by the clamping action of the wedges;
  • the wheel is positively located should that hoary ol'chestnut of the wheelnuts being stolen (but the motor is left behind :) )
    comes to pass, but
  • releasing the wheel for roadside puncture repair is easy, using minimal tools beyond those you would need anyway.
    (Keep the nail from your first puncture and you can use it to release the TA then next time :) ).
  • the design again seeks to supplement rather than supplant the existing dropout, and use spring energy to absorb
    and return the torque snap energy, rather than just butting heads with it.
The downside is complexity -- which is also cost -- but I have a few ideas about how to simplify it.

Enough's enough. I just heard a ding, which either means my sim has finished or failed or I left something in the microwave and forgot about it.

If I succeed in posting this despite half my previews being discarded, apparent temporary blacklisting -- "endless-sphere.com failed to return any data" -- and all the other ab .. er, anomalies, but don't get back for any reason, feel free to use it, or poo poo it as you see fit :)

Buk

Buk___
10 kW
10 kW
Posts: 713
Joined: Jul 28, 2017 5:59 pm

Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Buk___ » Apr 18, 2018 9:24 pm

Alan B wrote:
Apr 18, 2018 8:06 pm
Stooping to personal attacks? Wow. I expected better.
Since when is challenging your technical opinion, and the manner in which you deliver it, a "personal attack".
Alan B wrote:
Apr 18, 2018 8:06 pm
Good luck.
I don't need luck, I've got math & physics.

User avatar
Chalo
100 GW
100 GW
Posts: 6646
Joined: Apr 29, 2009 11:29 pm
Location: Austin, Texas

Re: The ultimate torque arm (For <2kW and standard axles)?

Post by Chalo » Apr 19, 2018 1:19 am

Buk___ wrote:
Apr 18, 2018 9:24 pm
I don't need luck, I've got math & physics.
One day you'll learn how to use them, kid. Best of luck with that.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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