Observed trials bike designing

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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speedmd   100 MW

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Re: Observed trials bike designing

Post by speedmd » Apr 26 2020 9:46am

A standard centrifugal clutch with a weaker spring would be a easy way to keep peak torque out and still have some lower rpm torque.
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Re: Observed trials bike designing

Post by john61ct » Apr 26 2020 10:24am

standard for what?

where does it go?

is it possible to say "limit torque to 150 N.m ?"

Sorry, if you could link to some basic learning resources I'd greatly appreciate it.

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Re: Observed trials bike designing

Post by Altair » Apr 26 2020 10:26am

Pete said: "I love the idea that Altair has talked about of rolling backwards downhill while applying forward drive with throttle alone - that would be awesome, but I'm guessing it would be brutally hard on the motor?"

No it's not, really. Not harder for the motor than holding still. And the current is not very high in that case, anyway. Totally unlike accelerating, for example. Don't worry about that.

Regarding Dan's mention of the secondary use of the clutch as a "panic button instant power off switch", the throttle itself still does that job admirably on an e-bike. It's really an instant "neutral" control, as quick as a clutch I would say. But still, different because of the lack of inertia of the whole drivetrain. When you do that going very slowly uphill, the bike goes instantly backwards, which is quite startling the first time. Conversely, if you do that with a clutched trials bike, there is a transition period between the clutch being engaged, and totally released, so you feel it coming, in a way. The second contributing factor is that the inertia of the whole bike is much higher on a motorcycle than on the e-bike. The motorcycle takes more time to slow-down, stop, and re-accelerate backwards. You have more time to react.
A couple times, I've had the controller turn off because of low-voltage detection on my first bike, during winter (cold batteries), on a slow steep climb, and I can tell you, the bike instantly slips out from under you, and you are not positioned anymore to save it, so... instant crash.

A concern I have about Pete's project bike is the mechanical strength of the bike, in a trials situation. The bike will be subjected to brutal accelerations, in all directions, and cracking of the frame might happen. Maybe not. I guess it depends on the rider... :lol:

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Re: Observed trials bike designing

Post by speedmd » Apr 26 2020 10:57am

john61ct wrote:
Apr 26 2020 10:24am
standard for what?

where does it go?

is it possible to say "limit torque to 150 N.m ?"

Sorry, if you could link to some basic learning resources I'd greatly appreciate it.
Sorry, hard to judge where folks are starting from at times. Tons of google results on them, so best to get that at where your at with understanding it. These are standard ICE small engine clutches used on most everything. Gokarts, power equipment, chainsaws and the like so they can idle freely. They go right on the motor shaft. The spring is tuned for a desired engagement rpm, so in a electric that does not need to idle, they could be set to a very low RPM just enough to soften the initial torque spike.

High limit may be limited by clutch size and stall speed torque - drag levels. Diameter, weight of the shoes, friction coefficients go into that so some testing would be needed depending on clutch selected. They are common and roll into junk yards all over by the truck load if you want to experiment with one on the cheap.

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Re: Observed trials bike designing

Post by DanGT86 » Apr 26 2020 1:21pm

john61ct wrote:
Apr 26 2020 9:06am
> recumpence's davinci drive. He uses a torque limiting clutch on the primary drive

Anybody got a link to that?

Very interested in anything that would tame a crazy-torque standing start

to protect a "fragile" drivetrain.

An actual physical slipping clutch would be very interesting, but I'm a complete noob there.
Matt shumaker aka ES member recumpence is probably in the top 5 most famous endless-sphere users. Do a search for anything called DaVinci drive or Astro motor and you will find him.
https://www.endless-sphere.com/forums/v ... 7&start=50

Here is one of his drive units.
davinci1.jpg
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The torque limiting device is a friction material sandwich with the large pulley. There is an axial spring that tensions the friction plates against the sprocket. You can thread the adjustment nut in to preload the spring with a range of squeeze to adjust the breakaway torque. The basic idea is that you have a motor that makes way to much power than you need at start up. Then you just tension the friction material on the clutch such that any extra torque allows it to break away and slip at a specific torque. It keeps amp peaks and drive line shock to a minimum and would make for a very consistent full throttle blast for trials type moves as well as keeping frames and chains and belts and mounts from cracking. Basically no matter how many amps you throw at the motor there is always a mechanical limit to what gets through to the wheel.

You can buy these torque limiters from mcmaster carr or other industrial supply places online.
torque limiter.png
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https://www.mcmaster.com/torque-clutches

as for the centrifugal clutches they are common on pretty much any go-kart or minibike supply place in the world. My fear with them would be getting the engagement rpm set low enough to be useful. Its nice that an electric motor can creep along at 5 rpm. Those clutches are usually in the hundreds of rpm. Seems like wasting a bit of range but depending on gearing it might be a solution.

I have heard ebike trials users complain that the absolute dead stop zero rpm power is a bit of a challenge. I do wonder if a rubber rag joint at the sprocket would be enough to overcome it. Anything to allow a few degrees of rotation to allow the controller and halls to sync seems like a huge benefit compared to trying to start a totally stopped rotor.

Regarding the low speed rolling backward stress on the motor. Just thrusting the bike forward or giving a half a crank revolution at launch is a noticeable difference in amp draw for the controller compared to a dead stop. The way I understand it the relationship between voltage and rpm is basically fixed. If power is the result of torque x rpm and torque is proportional to amperage than the math would indicate that at zero rpm the torque required is infinity for a set amount of power. I know that is not really how it works but generally my experience supports the idea that even a few rpm makes a noticeable difference in amp draw at super low speeds.

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Re: Observed trials bike designing

Post by speedmd » Apr 26 2020 1:35pm

Friction is good simple torque limiter for certain. Centrifugal also has the ability to freewheel, roll backwards a bit easier. A combination of the two on a clutch lever could be setup to release motor or engage it if springs were just reversed (compression vs tension) and cable pulled -(compressed) on springs.

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Re: Observed trials bike designing

Post by DanGT86 » Apr 26 2020 2:03pm

There is also some overlap in the different ideas. For instance, the slip in a centrifugal clutch is basically going to do the job of a torque based overload device. Given the large gulf between electric motor vs 5hp gokart ICE torque, im guessing the off the shelf kart clutches will slip as if they were torque limiters. Ay that point its just an issue of durability. They are designed for karts to be able to idle but spend most of their time locked. Just look at the difference in surface area compared to a mult-disk motorcycle clutch. The issue of duty cycle becomes apparent right away. Trials riding is going to be torture for a kart clutch that is designed to slip once or twice per race.

Once you switch over to hand cable operated clutch the overload device and launch control device are one in the same So any further weight and complexity is probably not worth it. If the maximum torque of an electric motor was just too much for all situations the rider could simply reduce the max current through the controller programing until they find the sweet spot be it limited by skills or traction.

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Re: Observed trials bike designing

Post by john61ct » Apr 26 2020 3:01pm

Thanks gives me good terminology for googlin.


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Re: Observed trials bike designing

Post by speedmd » Apr 26 2020 3:34pm

Jr class Gokarts run 28hp 125cc rotex 2 strokes and stall carts movement with the motor revving with gobs of throttle with brakes on and off for some time in the pits before heading out to race and still get many hours on clutch drums. It would not take much pressure to lock them up relatively tight. I don't think you can successfully stop the E. motors rotor fast enough without some controller or eddy current brake setup. The elite trials riders have the skill set already in their left hands, so I would plan on using it.

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Re: Observed trials bike designing

Post by bikerpete » Apr 26 2020 7:07pm

A flurry of ideas!

Guy, I'm also concerned about the ability of a bicycle frame to to deal with the forces of a clutched motor, particularly one with a flywheel added! My bike has a dogleg at the front of the swingarm to give chain clearance, I expect that to be the weak link. Luckily it's a fairly solidly made aluminium forging (maybe casting, but it looks possibly forged so I'll be optimistic). The suspension is split link design so making a new swingarm isn't tooooo much work if/when this one breaks, the seat stays are a carbon piece that I hope might survive a swingarm failure as they'd be a nuisance to recreate, although doing so would solve my rear sprocket diameter limitation.
As long as I don't get broken in the crash, I'm not too concerned about breaking the swingarm. The bottom bracket area that the swing arm pivots on is a significantly robust drawn and welded section - I'll be pretty surprised if that fails. Welded tube joints and the adjacent affected metal are always weak points on bikes - I'll just have to keep an eye on that for fatigue. If cracking starts to show I'll weld on some gussets I guess and turn it into a Franken Fat-e. I'm actually just as concerned about how the bike is going to stand being thrown away, as trials bikes tend to be from time to time (mine at least - self preservation at all costs these days).

As you say, it's probably got as much to do with how much restraint I can show as anything! I'm generally pretty easy on machinery, but on the other hand I do enjoy winding up the 300 a bit and clutching it at things. How I ride the Fat-e remains to be seen.

It's interesting you find the throttle almost equivalent to a clutch for that e-stop function. There are quite a few times I've gotten myself into trouble by whiskey throttling and it's only the clutch that's saved me (and even then not always) as once that whiskey throttle starts it's virtually impossible to stop it except by jumping off. With the torque of electric combined with the lightweight bike I'd have thought that could be an even bigger problem on these things.

I was out riding yesterday - raining, logs that have just lost their bark, so really slippery. It reminded me just how important that flywheel is - any throttle at all as the bike rolls onto the top of the log and the back wheel spins and instantly drops the front. Even if you think you're not going to make it, it's better to hold the throttle off and let the bike drop to the bash plate or slowly drop the front than be tempted to try to help it over with even the tiniest bit of throttle. Without the flywheel inertia I just can't come close to imagining how to ride that stuff - except by becoming a LOT better rider.

Certainly some of this last discussion encourages me further with my decision to put in a clutch. Getting halls synced? - slip the clutch a bit. Throttle a bit sudden off the bottom? - slip the clutch.
Just have to find the time to finish the design and start machining!

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Re: Observed trials bike designing

Post by speedmd » Apr 26 2020 7:33pm

Rotors on most of the electric motors per KW are near equal in rotational mass to ICE race motors. Overshoot! :shock:
A bit of clutch mass will mate well.

Long term, no doubt that throttle only, with brake and reverse (with the help of more advanced controller brain and proper programing of motion control) will far exceed basic mechanical solutions.

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Re: Observed trials bike designing

Post by bikerpete » Apr 26 2020 11:24pm

speedmd wrote:
Apr 26 2020 7:33pm
Rotors on most of the electric motors per KW are near equal in rotational mass to ICE race motors. Overshoot! :shock:
A bit of clutch mass will mate well.

Long term, no doubt that throttle only, with brake and reverse (with the help of more advanced controller brain and proper programing of motion control) will far exceed basic mechanical solutions.
I quite agree that full electronic replacement of clutch and flywheel could be achieved and provide a more flexible end result - I just don't see it happening any time soon - trials is about the only area I can think of that really wants the type of control we're talking and it's such a tiny niche market at this stage.

I sometimes wonder why there seems to be a bit of a black and white division between mechanical / electronic. It has often seemed to me that electronics oriented people want to solve every problem electronically when there can be a perfectly reasonable mechanical solution. How long would it take to tweak a capable controller to provide the characteristics inherent in a flywheel?
It's a bit of a, "Give a man a hammer and everything looks like a nail" situation. A flywheel is actually a pretty elegant solution to storage and delivery of power over shorter time periods. It's interesting to see how flywheels are growing in the bulk energy storage sphere.

Possibly the clutch alone will be sufficient extra inertia, but I don't expect so. The clutch is spinning something around 3 times slower than the motor so it's effect isn't so big, and it doesn't weigh much anyway.
I'd prefer too much flywheel and a slow motor response to the other way around. If the flywheel is too heavy it'll be easy to shave it down - harder to add weight on.
Added bonus of a flywheel that no amount of controller magic can replicate is that a spinning flywheel makes a handy gyroscope that aids balancing a stationary bike. A handful of throttle with the clutch in can help catch your balance.

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Re: Observed trials bike designing

Post by speedmd » Apr 27 2020 7:28am

I sometimes wonder why there seems to be a bit of a black and white division between mechanical / electronic. It has often seemed to me that electronics oriented people want to solve every problem electronically when there can be a perfectly reasonable mechanical solution
Thinking most have not fallen off a shear 12 foot tall rock pile on a bike weighing more than they do. :oops:

"It is most times easier the hard way" :lol:

Flywheel is risky at dialing out power impulse. Shows that the skills are high at this. There is a reason the AX is referred to as a "Noble" tool while the saw is just a tradesmans. Much higher skill set is required to achieve precision.

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Re: Observed trials bike designing

Post by rynhardt » Apr 28 2020 6:20am

I've been riding electric trials bikes for the last 3 years now and have become accustomed to riding without a clutch. I believe that it requires different technique but ultimately it comes down to preference. My preference is for low weight.

I've made some mods to address some of the issues I've encountered, two of them below:
  • Added a motor-cut out switch on the rear brake lever - useful for those whiskey-throttle moments.
  • Added a "boost" switch that enables a full-power throttle map - useful for doing splats.
Of course when you are designing your own bike, anything goes. Just some food for thought.
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Re: Observed trials bike designing

Post by bikerpete » Apr 28 2020 6:31pm

rynhardt wrote:
Apr 28 2020 6:20am
I've been riding electric trials bikes for the last 3 years now and have become accustomed to riding without a clutch. I believe that it requires different technique but ultimately it comes down to preference. My preference is for low weight.
The two switches look completely sensible. I haven't noticed a bike with a map switch right at your thumb. I might rethink my map switch so I can do something similar.

I haven't bothered doing any calcs on my design, simply picking stuff that gets good reports and fits. But I'm thinking my bike might be 1/2 - 2/3 the weight of yours, at maybe double the power and probably torque. My top speed at 3400 rpm will be under 40kmh. Hopefully the frame stays together for a reasonable length of time!

I do wonder about the sensibility of going to all the extra effort to add a clutch, but I just see too many advantages not to try it. If it's not needed I don't have to use it.

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Re: Observed trials bike designing

Post by DanGT86 » Apr 29 2020 9:22am

Hopefully Altair can chime in on this one. I'm curious what the foot peg position on a bicycle frame is like compared to standing on pedals. When I stand on a normal set of cranks I have one foot 170mm to the front and 170mm to the rear. This is a very wide platform and provides tons of stability even though the bottom bracket can rotate. A motorcycle is so much heavier that you can move your body around using the inertia of the bike so I would think having both feet trapped in line with each other would be less of an issue.

To those of you out there who have ridden bike frames with stationary pegs instead of pedals, what are your thoughts/observations about it?

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Re: Observed trials bike designing

Post by speedmd » Apr 29 2020 2:58pm

For Trials, the pegs are offset to the rear and set high and as inward as you can get for clearance. Crank puts you at potential disadvantage in both aspects. Fresh build could be set near anywhere you wish. Ideal would be a crank set that folds out of the way, and pegs that fold down for segment use.

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Re: Observed trials bike designing

Post by bikerpete » Apr 29 2020 6:20pm

DanGT86 wrote:
Apr 29 2020 9:22am
Hopefully Altair can chime in on this one. I'm curious what the foot peg position on a bicycle frame is like compared to standing on pedals. When I stand on a normal set of cranks I have one foot 170mm to the front and 170mm to the rear. This is a very wide platform and provides tons of stability even though the bottom bracket can rotate. A motorcycle is so much heavier that you can move your body around using the inertia of the bike so I would think having both feet trapped in line with each other would be less of an issue.

To those of you out there who have ridden bike frames with stationary pegs instead of pedals, what are your thoughts/observations about it?
As you say, Guy is best placed to provide informed comment, but ...

I used to teach MTB and rode a lot. Now that time goes into trials, when I ride my MTB now I usually am just as happy hopping and practicing trials as riding singletrack.
I think the feeling of stability you get from your pedal lead is perception only. As you say, they pivot on the bottom bracket bearing so really you are just balancing on that point. One time when I had the cranks off I just stuck a pipe through the bottom bracket and stood on that and rolled around - balance wise it felt not much different to standing on the cranks.

Balance is absolutely key for trials, yes you use the bars to push, pull and move about, but always trying to work from and return to a place of balance over the pegs.
Stability is the enemy of balance. For instance if you had a big flat plate to stand on, you'd have plenty of stability, but what happens when you stand the bike up on it's back wheel? Now that stable platform is pushing you out of balance, or has moved your balance point considerably forward from where it was. Actually there is a moto foot peg available that pivots on bearings like a pedal - a lot of people like them.

Peg width (distance apart) is a bit of a compromise between narrow for clearance to obstacles and wide to give room for the bike to move beneath you. On moto's it largely comes down to the width of the gearbox.
On my e-trials bicycle I'm finding I probably need to move the pegs out a tiny bit further than the mechanical minimum so I can move the bike around between my legs enough. If the frame was a dedicated trials bike the pegs could probably be narrower. I actually considered using a set of MTB flat pedals for pegs - nice big grippy platforms that won't upset your balance, but competitions require folding footpegs to reduce the risk of injury.

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Re: Observed trials bike designing

Post by macribs » May 02 2020 6:26am

DanGT86 wrote:
Jan 31 2020 10:31am
You could even theoretically cheat and implement traction control if you had precise enough sensors of wheel speed and load.

I have often thought it would be cool to make the throttle output to the controller the sum total of a rising and falling voltage from the throttle and a fake clutch lever (no actual clutch). In this case full throttle with the clutch in would yield no throttle output. Inversely full throttle with the clutch lever released would be max power. In this case it would feel like a normal bike where you still modulate power with the clutch in precise situations like trials. Its easier to squeeze a lever under rough conditions climbing and hopping than it is to precisely angle the throttle while pulling on the bars.
Just a thought.

An actual mechanical clutch might still be more natural for experienced riders with years of muscle memory.
As electric motion launched this year electric trials bike with a clutch and a flywheel with adjustable weights it is hard for me to imagine en fully electric trials bike performing as well without flywheel and clutch. Because Electric Motion has been producing electric trials bike for a while now, not using clutch and flywheel much like Oset does. But this year they changed to flywheel and clutch and it seems those that have ridden the new bike with clutch and a flywheel are raving about them.

What the OP said about only the stored up energy from the spinning flywheel drives the rear wheel seems to make sense. Imagine riding up rocky slippery river/creeks/brookes, if you are to take on a 3 feet or even 5 feet vertical wall on those wet and slippery conditions wheel spin will not be your friend. And they ride in mud and other slippery surfaces too. I think there is benefits from using flywheel and clutches on electric trials bikes.

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Re: Observed trials bike designing

Post by bikerpete » May 02 2020 6:46pm

I was thinking about electric "clutches" as EM used previously (and still on the lower models I think?).

Perhaps part of the reason they don't work as well as a mechanical/flywheel combo is that they are working within the constraint of the throttle ramp settings?

To have a manageable throttle there must be some ramping, but for the clutch we want none.
How about a switch on the clutch lever that when the lever is pulled switched the controller to no-ramp mode. This might make the effect of pulling and releasing the lever more similar to a mechanical.

Still doesn't solve the flywheel issue, but it's possibly achievable today.

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Re: Observed trials bike designing

Post by DanGT86 » May 02 2020 7:36pm

As I understand it that is exactly what the E-clutch does. It gives you access to a ramp rate that would be annoying in the normal twist throttle.

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Re: Observed trials bike designing

Post by bikerpete » May 03 2020 3:03am

I don't know, I'm making some largely baseless assumptions, but I thought that what the old EM "clutch" did was basically just add a 'negative' throttle on the clutch lever, so the total signal to the controller was the sum of the 2 outputs. It doesn't alter the controller internal throttle ramp.
I'd expect that there is some degree of throttle ramping or smoothing set in the controller or the throttle would be too hard to operate smoothly and accurately for trials use - could easily be wrong on that. If this is the case, then dumping the clutch will only provide an increase of amps/torque as fast as the controller ramp setting allows.

What I was suggesting was that at the start of the clutch pull there'd be a switch that actually changed the controller to a mode with absolutely no throttle ramping/smoothing. The rest of the stroke continues to operate as a 'negative throttle. The difference would be that when you release the clutch the controller would not be applying any ramping, but increasing current as fast as it possibly could. Once the clutch is fully released (or wherever the switch point is set to) then the controller would turn on ramping again so the throttle is manageable. For that matter the switch could even change the controller from torque mode to speed mode which should cause it to try to jump to the main throttle speed setting. The rate of release of the clutch lever would be the sole moderator of amps/torque increase - within the limits of the controller obviously.

On the Nucular this would be pretty simple to achieve, no idea with other controllers, and also no idea how instantaneous and seamless the transition from one mode to another is when under power.

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Re: Observed trials bike designing

Post by rynhardt » May 03 2020 4:23am

macribs wrote:
May 02 2020 6:26am
DanGT86 wrote:
Jan 31 2020 10:31am
An actual mechanical clutch might still be more natural for experienced riders with years of muscle memory.
As electric motion launched this year electric trials bike with a clutch and a flywheel with adjustable weights it is hard for me to imagine en fully electric trials bike performing as well without flywheel and clutch. Because Electric Motion has been producing electric trials bike for a while now, not using clutch and flywheel much like Oset does. But this year they changed to flywheel and clutch and it seems those that have ridden the new bike with clutch and a flywheel are raving about them.
I suspect the major factor in the decision to use a flywheel and mechanical clutch is the broader consumer appeal. Not everyone wants to adapt their riding style for the sake of saving a few kg.

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Re: Observed trials bike designing

Post by bikerpete » May 03 2020 5:36am

rynhardt wrote:
May 03 2020 4:23am
I suspect the major factor in the decision to use a flywheel and mechanical clutch is the broader consumer appeal. Not everyone wants to adapt their riding style for the sake of saving a few kg.
EDIT:
I wrote a bunch of stuff, but I more or less agree with you.
With the exception that saving the few kg is largely insignificant compared to losing the ability to do what a clutch & flywheel allow you to do, and that no current controller allows.

I'm hoping my build will save a good 30kg + over an ICE trials bike, and have a clutch :thumb:

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