Gyroscopic effect and hub motors

[Green Machine]

SO i have been experimenting with different motor configurations on an identical frame, fat tires and wheels and had some interesting observations that i would have not gotten otherwise.

IT seems the gyroscopic effect created by the large and heavy rotating mass of the hub motor is a factor i never considered and its considerable.

Here are the different motors i have mounted on an identical frame:

*Astro motor mid drive

*Rear Hub Motor (large diameter 9c)

*Front hub motor (bmc)

*MId drive motor (bmc)

Surprisingly all these very similar bikes have totally different handling characteristics relative to their motor position.

When riding with any of the hub motor bikes the bike tries to right itself when cornering because of the gyroscopic effect. It took a long time to figure out what this sensation is, but when you lean into a corner it feels like the bike is fighting you.

The most pronounced gyroscopic effect by far is the mid drive mac motor bike. You really feel it like the bike wants to high side you. WHen first riding this bike we all thought something was loose in the bike. Its handling is severely effected.

In the front wheel drive bike when you corner it does weird things with the steering as you lean into corners. You feel it 2nd most in the front wheel drive.

In the rear wheel drive you can definitely feel it but its not a big factor as it is in the front wheel drive and the mid drive.

IN the astro set up the motor which is lightweight and small the bike handles like a dream. It feels like a different bike than all the others when it comes to cornering.

Perhaps the gyroscopic effect is not a big deal and just is a matter of getting use to. Maybe its actually a good thing, the bike has a natural tendency to ride right side up. I am not sure. I am almost sure that the gyroscopic effect is a bad thing in a front wheel drive bike.

I need more ride time with the mid drive bike to see how this severe gyroscopic effect changes things.

THe important thing for me was to realize that the gyroscopic effect was there, so as not to think it was my choice of tires etc that was causing it. Also when i know its there i can compensate by leaning harder into corners without feeling like i am forcing something like a tire tread issue.

According to the mechanical engineer i am working with (who specializes in motorcycle design) the gyroscopic effect is more severe in a bike with the large rotating mass near the center of gravity. Therefore the lower the motor is mounted in a mid drive the better. And of course the smaller and lighter the motor the better. Motorcycles have this too...some much more than others.

I would be interested to see what the ES brain trust thinks about gyroscopic effect when it comes to hub motors. Hub motors tend to be large and heavy so gyroscopic effect should be big factor.

How does it change things with say a stealth bomber when you have 38 pounds in the rear wheel?

 

[neptronix]

Hm, i never noticed any detrimental effects from hub motors.
Fact is, we corner faster than most bikes will, so turning will be perceived as being more difficult..

 

[John in CR]

"Severe gyroscopic effect". Come on. Time to hit the calculator to see the far greater effect of a motorcycle tire and rim which have considerable weight at a far greater radius. I'm not saying that you can't feel a MAC with pounds of rotor spinning at thousands of rpm in the middle of a bike, but "severe" ???, and a low rpm hubmotor at the wheels would fall under the adjective "minimal". My 40+lb motor wheel spinning at hundreds of rpms accelerating out of curves never tries to high side me just like it has no effect at over 1000rpm following a curve on the highway. It's just a natural part of turning. I also can't say I can feel my 20lb mid-drive with an axle mounted 22" above the ground and it turns 1krpm, nor can I feel it while doing a doughnut at WOT in the grass.

Are you one of those guys who can feel the effect of 100 grams on a non-motorized bicycle?

Sorry couldn't resist having a bit of fun with you.

I need to get you on a high power bike, so you can focus on the throttle and brake before you give the lycra patrol the idea that ebikes should be banned because gyroscopic effects make them dangerous.

John

 

[Green Machine]

On the middrive hub motor bike iIt's strong enough to where you feel something has come loose on the bike. The pull is pretty strong. The steering really feels wacky.

Also first time i rode the front wheel hub motor version of the bike it felt dangerous cornering until i got use to it. The bike fights you in corners.

IT becomes clear when you try identical bikes with different motor configurations. Then it all became clear what i was feeling.

LIke i said, i felt it before but always attributed it to tread choice etc.

with a bmc motor mounted in the center of the frame (close to center of gravity) with that large spinning mass it is more than noticeable. Yes i would call it severe.

I dont know what to think of it if its good or bad....maybe it just takes getting use to. The astro mid drive at this point handles much much better.

 

[neptronix]

Have you got your batteries in a rear rack, by the way?
I have mine up in the front triangle. Versus an ordinary bike, i can't tell the battery is there while riding it.

 

[MattyCiii]

"...Time to hit the calculator to see the far greater effect of a motorcycle tire and rim which have considerable weight at a far greater radius.
John

Let me second that!
My A-Line comes in just under 100 lbs. Much closer in weight to the 50 lbs or so my folding bike weighs. But since I'm using 21" motorcycle tires and rims, the bike feels exactly like my Honda Shadow, 550 lb cruiser motorcycle.
Talk about gyroscopic effect!

 

[MadRhino]

My V10, of which half of the total weight is the X54 hub motor, corners and handles real nice. Its only problem is that it wants to be a unicycle most of the time.

 

[Ypedal]

A picture of the test bike would be nice.

suspension ?..

power levels used ?

Personally, a regular bicycle vs ebike handling are oranges and apples, not to be compared.

my collection of bikes, hub and chain driven Astro, all handle differently, seat height, handlebar positions, wheel sizes, with or without suspension all feel different.. duuh..

How " significant " and the level of importance it brings, i'm not sue i get your point.,

edit to add : as far as gyro effect, it's only an issue if you are racing.. and 500w races are not exactly the most fun i can think of lol..

 

[Green Machine]

Well my collection of bikes consist of the same exact frame, the same exact suspension, the same exact handlebar height, the same exact battery mounting position (low above the bb), same exact battery.....just different motor configurations.....how often on ES do you get that?

4 identical bikes with different motor systems?

Anyway i guess my point was to share some interesting data. The bikes with different motor positions handle completely differently because specifically of gyroscopic effect. I am just posting my findings and trying to get some feedback on how it effects things. I guess no one else has felt it. Come to california if you want to feel.

A group of riders, one being a phd in mechanical engineering who designs motorcycles rode the bikes together back to back and felt the same sensation.

Its first of many data points I had to share....

Here is the astro bike



Here is the hub motor mid mount where gyroscopic effect is largest:

 

[Ypedal]

i am unable to quote you the math formula but i know form experience that the faster something spins, the more pronounced the gyro effect is.

a Hub motor in the wheel will spin slower than one mounted to the frame with a gear ratio, so for the same weight, an object spinning at a higher rpm will create a more pronounced effect on the bike..

 

[Sancho's Horse]

Green Machine, love the four different setups on identical bikes. Thats after my heart there.

I have been considering the possibility of a gyroscopic effect on mid-drive hubmotors in their peak rpm efficiency for a long while now. That is why I am making my setup modular because I also have been in the parts gathering stage of a future build, a mid-drive leaning balls to wall semi-recumbent tadpole trike.

So, my thought was that this effect is definitely there, and might be used as a design element in the self correcting mechanism of the trike. This would allow a couple of geometry changes, hopefully. You are the most qualified person here for this question. Is the effect significant enough to integrate design wise?

Dude, I got to get the feel for it myself. Space on the couch?

 

[amberwolf]

i am unable to quote you the math formula but i know form experience that the faster something spins, the more pronounced the gyro effect is.

it also depends on the mass--you can have a massive gyro at a slower speed or a smaller gyro at a faster speed and hve quivlaent effect.

 

[dogman dan]

I couldn't quantify it, but when running a 3000w front hubmotor on the racetrack, it definitely cornered very differently than a normal bike. But to be honest, I was mostly just noticing that I'd better get on the throttle later in the corners to avoid drifting the front tire.

I have noticed the gyroscopic effect before though, on regular bikes. Generally a lot more noticeable the faster you have the wheels spinning, such as gravity racing down a steep road in the rocky mountains. The faster you enter a corner, the more you have to force it to lean. On a motorcycle, with more mass in the wheels, I had a hard time with it when first learning to ride one. I was used to light bicycle wheels. I had to learn to throw more weight into the corners. In half an hour, I had the hang of it, but that first ride was scary.

 

[rocwandrer]

It is said that there is a psychological phenomenon where we are much more likely to come to a particular conclusion if we anticipated it than if we entered a study blind to potential outcomes. I've experienced this personally to some degree, and I think no one is immune.

That probably makes it sound like I'm disagreeing, and I'm not, actually.

Mechanical engineer here, with a fatbike, been through 12 fat tires at this point. Constantly messing with tire pressure. The gyroscopic effect of just those rims and tires alone is enough to actually be felt, and my butt dyno isn't all that sensitive (usually don't notice 300g change in bike weight, or 10 hp in a car, etc).

Can I suggest that your control over having it be the same frame and so on, while important, is not actually nearly as important as 2 psi of tire pressure with that type of tire? To those without fat bike experience, this probably sounds crazy... I cannot feel a 10 hp improvement in a car (unless it comes with extra noises ), but I can feel (and not "just barely" either) the effect of 1 psi in my fat tires on cornering.

Those spider tires are not nearly so bad as their novelty origins would have one guessing, but they do corner a little more funky at low pressures. I actually like my spider for the mix of driving traction and not breaking the crust up that it gives on semi-packed snow conditions. That said, I can't imagine doing a controlled test of cornering with those tires. Another point. Because of the thermal expansion coefficient of wet air, tire pressure changes a bit with temperature. I haven't done the math on it, but I've noticed that my tires can be pumped up to pavement use pressures in my office, and then 5 minutes down the path they feel like I got a slow leak. I think perhaps the CTE disparities in the materials involved make this effect more extreme than in a car tire, but regardless, I've noted this effect is quite extreme in these tires.

So I'm not disagreeing with you so much as asking

1.) do you have any other tires to test with? (black floyd or larry would be my picks)
2.) did you rigorously control for tire pressure during your back to back tests? I know anyone would want to say yes, or it is not an issue, but truthfully, is there no possibility that tire pressure is confounding your experiments?

 

[Green Machine]

1.) do you have any other tires to test with? (black floyd or larry would be my picks)
2.) did you rigorously control for tire pressure during your back to back tests? I know anyone would want to say yes, or it is not an issue, but truthfully, is there no possibility that tire pressure is confounding your experiments?

NO i only have tried one type of tire. But the astro bike has a surly endomorph on the back, so that could be a factor on why it handles so well but i doubt it. Having ridden on both the endomorph and the spider tire, the spider corners better (it is better rounded). I am getting a spider tire (laced for its rohloff) built for its rear and we will know for sure then.

We did not check tire pressures, but it did not feel like a tire pressure issue.

I will have both the astro bike and the mid drive hub bike together for a lengthy test ride in the next few days and can report back then.

I dont know if i mentioned this, but it is a geared bmc motor converted to mid drive with the crossbreak method. The 10 pound motor is spinning with a 6 to 1 reduction. Its a lot of fast spinning mass to have mounted in the bikes center of gravity. WHen i have the bike going again i am going to try cornering with the power off and on and note the difference.

 

[rocwandrer]

1.) do you have any other tires to test with? (black floyd or larry would be my picks)
2.) did you rigorously control for tire pressure during your back to back tests? I know anyone would want to say yes, or it is not an issue, but truthfully, is there no possibility that tire pressure is confounding your experiments?

NO i only have tried one type of tire. But the astro bike has a surly endomorph on the back, so that could be a factor on why it handles so well but i doubt it. Having ridden on both the endomorph and the spider tire, the spider corners better (it is better rounded). I am getting a spider tire (laced for its rohloff) built for its rear and we will know for sure then.

We did not check tire pressures, but it did not feel like a tire pressure issue.

I will have both the astro bike and the mid drive hub bike together for a lengthy test ride in the next few days and can report back then.

I dont know if i mentioned this, but it is a geared bmc motor converted to mid drive with the crossbreak method. The 10 pound motor is spinning with a 6 to 1 reduction. Its a lot of fast spinning mass to have mounted in the bikes center of gravity. WHen i have the bike going again i am going to try cornering with the power off and on and note the difference.

My experience is that front tire pressure is incredibly critical to rider confidence in cornering and even straight line stability over rough ground. Rear tire pressure has a secondary effect on handling that is noticeable, but not really scary (then again, i am far more comfortable with oversteer than understeer, and more scared of a highside than a lowside.)

I have a couple suggestions and a comment. I suggest getting a pressure gauge that has excellent repeatability (accuracy doesn't really matter much) and using it to verify both bikes are at the same pressure. If you want to focus on gyro effects, I suggest 15 psi as a minimum. When you run your power vs no power back to back test with the mid drive, if you can disconnect the drive chain or run it backwards freewheeling or something, you will decouple the effect of driving torque from the gyroscopic effect of a spinning mass. If one wants the truth, it is always better to change only one parameter at a time when making comparisons and drawing conclusions. Thank you for sharing your test results on this. Interesting stuff!

 

[Sancho's Horse]

rocwandrer - good point on the tire pressure...and unfortunately the psychological analysis. I was expecting there would be a gyroscopic effect with more of these hubs in mid-drives, with the hubs seemingly getting bigger, and spinning closer to their optimal rpms...so, of course, I just ran with it mentally.

dogman - I hadn't considered the downside of the gyroscopic effect in high speed turning. The way that I pictured it "in my mind", with the ebraking, and hydraulic disk braking I am going to use (and would be maybe more pronounced with regen?), the motor would be slowed during turns enabling easier leaning in turns. Then accelerating out turns, if the weights were properly balanced against each other, the additional gyroscopic effect could tip the scale to an upright position helping bring you out of a lean. Maybe just a slightly better fatigue envelope. However, the big problem I picture with anything leaning is, intuitively, it seems like little differences in engineering could have a dramatic effect on the levels of rider fatigue being experienced, and thus enjoyability.

Love the discussion. I have a really good paper that I was able to get a student to request for me. It has been a year and a half though, but I will see if I can find it. May be useful to the discussion.

 

[rocwandrer]

rocwandrer - good point on the tire pressure...and unfortunately the psychological analysis. I was expecting there would be a gyroscopic effect with more of these hubs in mid-drives, with the hubs seemingly getting bigger, and spinning closer to their optimal rpms...so, of course, I just ran with it mentally.

dogman - I hadn't considered the downside of the gyroscopic effect in high speed turning. The way that I pictured it "in my mind", with the ebraking, and hydraulic disk braking I am going to use (and would be maybe more pronounced with regen?), the motor would be slowed during turns enabling easier leaning in turns. Then accelerating out turns, if the weights were properly balanced against each other, the additional gyroscopic effect could tip the scale to an upright position helping bring you out of a lean. Maybe just a slightly better fatigue envelope. However, the big problem I picture with anything leaning is, intuitively, it seems like little differences in engineering could have a dramatic effect on the levels of rider fatigue being experienced, and thus enjoyability.

Love the discussion. I have a really good paper that I was able to get a student to request for me. It has been a year and a half though, but I will see if I can find it. May be useful to the discussion.

This will seem totally off topic.... Big fat low pressure tires with minimal tread let you float on top of packed snow instead of breaking through. If the snow is loose and fluffy, and all tires are cutting down to the surface underneath, the skinniest, most aggressive treaded tire is usually the best choice. One of the huge harder to see/quantify advantages of the big fat low pressure tires is actually in situations where you are between the two former situations. While the skinny tire may actually have less rolling resistance, the total system energy required to make forward progress, perhaps even without including mental effort, can be substantially less with the fat tire. I think that the reason is that the bike is less skittish/prone to wander, and so the rider expends less energy making the bike go in the correct direction. Over a very short distance, it can seem obvious that the skinny tire is faster, if a little more frustrating. And yet over a long distance, the fat tire biker can just keep plodding along where the skinny tire biker in the same physical shape gets off and walks.

All of that to illustrate the point that unexpected/unnatural/conflicting control input parameters can have a detrimental impact. As an engineer, I love abs and traction control. As a racecar driver, i disable ABS, dislike traction control, hate progressive throttle linkages, and so on, because the complicate the business of getting the job done, and interfere with the natural progression of input/feedback/response in an... how shall i say... inorganic way. The basic mechanics of a lean steer vehicle are extremely complex, yet the experienced rider does all that it needed (countersteer initiation, cg correction, micro speed vs lean angle vs steering input corrections, etc) all without thinking. Add in a gyroscopic effect that is a function of speed and/or braking and so on, and it might well complicate more than it helps.

One of the biggest challenges I have not faced down yet in motorsports is that of aerodynamic downforce. things like being able to negotiate a corner at between 75 and 80 mph, or at not more than 60 mph. Things like the brakes working disproportionately less well at lower speeds, and having less compression travel available at higher speeds, these are the sorts of things that are an art not easily learned. The payoff of learning them is huge, however, so we do. I hypothesis that variably gyroscopic effect is similar, but rather than being a benefit to be capitalized on, like downforce, it is a detriment to be minimized and/or made more predictable where possible. Not that I don't hope I am proven wrong, since it is an interesting premise.

 

[geeeyejo1]

Related topic - and perhaps related to the gyroscopic effect: Does anyone know what causes a two wheeled bike or motorcycle to have to be "counter steered" (ie having to lean into the turn and actually push handlebars in opposite direction) when at speed? I remember when I went for my motorcycle certification and they discussed the concept - sounds totally crazy (I have to steer in the opposite direction of the turn???) but totally true. Not sure what the "magic speed" is but there is the point where instead of pointing my wheel in the direction I am going; I have to lean and push on the grip on the side I am turning into... Have experienced this on some steep downhills with my non-motorized bike and really looking forward to experiencing this again on my soon to be road worthy E-bike as it's been a few years since I sold my motorcycle and haven't ridden since...

 

[Green Machine]

Regarding fat bikes and tires.

I too experimented with many different fat tires on bikes and was not satisfied with handling. I was ready to give up on fat tires all together.... until my astro mid drive was completed. The bike handles so good. At first, I attributed it simply to the lower weight of the astro system.....6.5 pounds vs a 15 pound 9c hub motor (in the wheel).

With fat tire bikes the tire is much higher...we measured it 29 inches even though it is on a 26 inch rim. So the gyroscopic effect is even greater.

The front wheeled drive bmc bike is a bitch around corners...and i always thought it was the tires and now i think different. The bike is a great straigh away rider...but once you start to corner at higher speeds it becomes dangerous.

In the rear wheel bike I have a direct drive 9c motor and you dont feel it trying to straight itself around corners as much...in fact it feels very rideable.

It is the wobbly feel of the mid mounted bmc that made a true believer out of me.

Well i believe in gyroscopic effect in hub motor bikes and have experienced it first hand. Will experiment with it further later in the week when all the bikes are together again.

 

[rocwandrer]

Related topic - and perhaps related to the gyroscopic effect: Does anyone know what causes a two wheeled bike or motorcycle to have to be "counter steered" (ie having to lean into the turn and actually push handlebars in opposite direction) when at speed? I remember when I went for my motorcycle certification and they discussed the concept - sounds totally crazy (I have to steer in the opposite direction of the turn???) but totally true. Not sure what the "magic speed" is but there is the point where instead of pointing my wheel in the direction I am going; I have to lean and push on the grip on the side I am turning into... Have experienced this on some steep downhills with my non-motorized bike and really looking forward to experiencing this again on my soon to be road worthy E-bike as it's been a few years since I sold my motorcycle and haven't ridden since...

Ignoring your nomenclature, there are at least a dozen factors there. One is trail vs steering angle. Another is differential slip angle across the bias ply generating a turn in thrust.

I've never heard countersteer used to describe what you are talking about. I think in basic motorcycle courses in the US, countersteer means initiating a turn in one direction by steering in the other direction initially. Another meaning for counter steer is turning the steering in the opposite direction of the intended turn (or just less than the turn radius would imply) to compensate for a greater slip angle at the rear than at the front.

 

[rocwandrer]

Regarding fat bikes and tires.

I too experimented with many different fat tires on bikes and was not satisfied with handling. I was ready to give up on fat tires all together.... until my astro mid drive was completed. The bike handles so good. At first, I attributed it simply to the lower weight of the astro system.....6.5 pounds vs a 15 pound 9c hub motor (in the wheel).

With fat tire bikes the tire is much higher...we measured it 29 inches even though it is on a 26 inch rim. So the gyroscopic effect is even greater.

The front wheeled drive bmc bike is a bitch around corners...and i always thought it was the tires and now i think different. The bike is a great straigh away rider...but once you start to corner at higher speeds it becomes dangerous.

In the rear wheel bike I have a direct drive 9c motor and you dont feel it trying to straight itself around corners as much...in fact it feels very rideable.

It is the wobbly feel of the mid mounted bmc that made a true believer out of me.

Well i believe in gyroscopic effect in hub motor bikes and have experienced it first hand. Will experiment with it further later in the week when all the bikes are together again.

I have significant experience with fatbikes on pavement without any sort of electric motors or batteries, and I think they handle... very poorly at best... on pavement. Even with really high pressures. Even with lighter rims. That's just part of the charm

 

[geeeyejo1]

... I think in basic motorcycle courses in the US, countersteer means initiating a turn in one direction by steering in the other direction initially.

Yes - that's exactly what I am referring to - it's been a few years since I took the course but believe the term they used was "countersteer" - from Wikipedia:
"Countersteering is the technique used by single-track vehicle operators, such as cyclists and motorcyclists, to initiate a turn toward a given direction by momentarily steering counter to the desired direction ("steer left to turn right"). To negotiate a turn successfully, the combined center of mass of the rider and the single-track vehicle must first be leaned in the direction of the turn, and steering briefly in the opposite direction causes that lean."

 

[rocwandrer]

... I think in basic motorcycle courses in the US, countersteer means initiating a turn in one direction by steering in the other direction initially.

Yes - that's exactly what I am referring to - it's been a few years since I took the course but believe the term they used was "countersteer" - from Wikipedia:
"Countersteering is the technique used by single-track vehicle operators, such as cyclists and motorcyclists, to initiate a turn toward a given direction by momentarily steering counter to the desired direction ("steer left to turn right"). To negotiate a turn successfully, the combined center of mass of the rider and the single-track vehicle must first be leaned in the direction of the turn, and steering briefly in the opposite direction causes that lean."

So i must be misunderstanding. What's the question?

 

[amberwolf]

II have noticed the gyroscopic effect before though, on regular bikes. Generally a lot more noticeable the faster you have the wheels spinning, such as gravity racing down a steep road in the rocky mountains. The faster you enter a corner, the more you have to force it to lean.

Ah, but htere you also have another effect--centrifugal (maybe centripetal?) force acting on evertying of the vehcle and rider that's above the road surface, moreso the higher off the ground it is, which also increases with velocity or mass. even if you had no spinning motors or wheels but just skids you'd still have a harder time leaning into a corner at a faster speed than at a slower one.

i dunno if the gyroscopic effect of wheels/etc would be significantly greater or even lesser than than the cetrifgula force of the turn itself.