Trials Hub Motor for Two Wheel Drive?

[betarambo]

I finished my first build and the bug has stuck! I can't stop building electric trials bikes! My daughter is very happy with her hub motor trials bike.

So I need a new project. A hub motor trials motorcycle for an adult would be rare. I haven't seen any other trials bikes with hub motors so maybe there is only one so far. But to make the project really unique I need to go further.

And the winning idea is...

Two wheel drive. The hub motor is really perfect for this. Lots of people have done it on bicycles. Some people have done it on gas powered motorcycles. The beauty of the hub motor here is no chain or gears or shafts, just wires. The fun of trying to figure out how to control the two motors is very appealling too. I am thinking two controllers for sure. The fun comes with working up some sort of "electronic adjustable differential" between the two controllers. There are lots of possibilities from simple two wheel drive on those loose hills to switching to front wheel drive only with back brake on to be able turn as tight as hopping the front wheel.

So I need your help. My kid's bike is running about 2600W through a Magic Pie 2. I don't think I want to try to run that same motor on a bike for a full size man. I am thinking I will need maybe 10kw in each motor to be able to ride the things I ride on my gas bike. I know people do pump that much power through pies, but in trials we go super slow so there is not a lot of cooling air, and I can only guess what the efficency might be when you are that far over specs.

So what motor would you recomend? I am hooked on hub motors so save your breath. Yes, I have heard about rolling resistance and unsprung wieght. Yes, I see the benifits of gearing. At the end of the day, getting drive to the front wheel is just plain hard in any form other than a hub motor.

I looked at the Enertec motors which look great. However, if I am going to run two fo them it feels like I might have more weight and spend more money than I need for the power I can really use. From the applications they show I am thinking that this motor would be good if I was using one, although they might be wound more for speed than acceleration.

So I think my needs might be:
1. Hub motor
2. 10 kw or so
3. Direct drive
4. Wound for torque
5. Durable for shock

I might be asking for too much, but then again your wealth of knowledge got me through my first build so the sky is the limit!

Gwhy, hook me up! (even if I am a little nutty to try a hubbie for real trials)

[gwhy!]

Hi Beta,
I really like how your small version trials turned out , and now you want to take it further, Thats e-bikes for you . The 2wd system have been played with like you say with gas engines and from what I read about some of the top riders having some peg time on these development bikes the riders did not like it for various reasons, but that said they would not have had independent control over the power from front to back which may make all the difference. Sorry I cant help you select a hub motor for the job, but like you say you may have to get one wound for torque and not speed as fitting a hub into smaller rims is not a option on a full size bike. I dont think you will need such a powerful hub on the front ( maybe the pie will be enough ~2kw ) but you will need around the 6-8kw for the rear ( if the top speed is around 25-28mph ). The nice thing about using independent motors for a 2wd system is that the control to the motors can be tweeked to find the optimum setup for 2wd which is something that is very hard to do with a gas engine. Good luck, and I will be following you progress .

[betarambo]

Thanks man. I am pretty much pinning my hopes on the idea that the independant control will keep it from being just another lame idea. I like the idea of just using a pie for the front since you are right about the reduced power needs. Maybe an Entertec for the rear and a pie on the front will do.

I am thinking that I might start with just a front conversion. Maybe I can slap a pie on the front of a gas bike and ride it some with gas for the rear and electric for the front. It might be a tricky proof of concept to control with the clutch and front throtle on one side and the front brake and rear throttle on the other. Should make for some good videos!

I have an extra Lyen 12 fet controller and my daughter will probably loan me some batteries so I could probably pull off a proof of concept for a few hundred bucks.

I am thinking that the front tire should actually be a rear tire. I have been thinking about why motorcycles have larger diameter front rims than rear when the overall tire diamter ends up about the same. I am thinking that maybe they do this because you need a shorter sidewall on the front because trying to turn with power form the rear would tend to fold the sidewall over. If my model would have me pulling the front around with front drive instead of pushing it then I can live with the extra sidewall flex and pick up extra traction in the process.

I think the biggest issue with this would be fitting the 4" wide tire between the forks. It might mean spacing the forks further apart. That would require buying some more beer for the machinist guys as work, but it could be done. I guess the proof of concept should use a regular front tire for starters.

Oh, snap! The big issue for the proof of concept is torque arms! Unlike the handy slot on the swingarm, the front forks have a round hole for the axle. For the proof of concept (POC) I don't want to do anything that I can't undo so my first thought of welding in some inserts is out. I guess maybe I can make up a couple of arms out of some plate and just clamp them to the fork legs with a few hose clamps or something. As long as I don't go too far with the power that might suffice for the POC.

Dang, more problems just keep popping into my head. If I put much power through that front drive with forks not designed to be pulled that way I wonder if I might find some issues. They might flex forward and make the action not so smooth or maybe eventually wear on the bushings. Maybe revision 7 or so of the POC could sort that out with a front swing arm or something equally goofy.

[gwhy!]

Yes, should be pretty easy to do a POC with a gas bike with a hub on the front ( lots of video please, while you are getting used to it ), like you say standard front wheel first ( or maybe even a 24" wide bicycle rim with a 3" tyre will do the job for testing ).

[hjns]

Nice idea. I would put little less power in the front. Something like a 9C 2807 in front and a cromotor in the rear. For driving slowly and getting enough power, go for at least 18FET 4110 and preferably larger in the rear. You may end up with something like 6-8kW in the rear and 2-4kW in front.

[Bluefang]

An idea would be to use John from CRs hub in the rear. thats good for 6kw+ right out of the box and you can run a really fat 10" off road scooter tire viewtopic.php?f=31&t=40859

For the front wheel i would think a hub with a really slow wind would be a good idea as you would be best running up to 100V and the higher torque of the slow wound motor would be more useful in a large front wheel. FYI a 26" bike rim JUST fits on a 21" front motorbike hub and spoke setup so i would think you could mount a 21" motorbike rim on the spokes from a 26" hub. They did testing on 2wd motorbikes and found that the front wheel only needed a max of somthing like 20% of the rear wheels power and to make a difference it only needed 5%.

[Alan B]

I was thinking Pie in front and Cromotor in rear. The Croatia folks are working on a motor that is like a bigger pie that might make a better choice for the front or even both ends. For these low speed torque situations you want large diameter motors and small diameter tires.

Cooling may be the problem, make sure to have temperature sensors in the motors.

[gwhy!]

away of controlling the 2 motors could be to use something like I have done on my bike a e-clutch lever but use the regular throttle for the rear and use the e-clutch lever for the front power, if nothing else, it will make it interesting to ride

[hjns]

I would prefer one or two 3-speed switches, that allow you to use a maximum of 9 different combinations for front|rear motor speed. Having a fast (f)|fast(r) combo would be applicable only for long tarmac stretches to get the highest topspeed. A slow (s) | slow (r) combo would be practical for very technical trails. A slow (f) | fast (r) combo would be appropriate for some average riding, whereas an intermediate (f) | fast (r) combo could be used for steep hills. I don't see any uses for a fast (f) | slow (r) combo.

[gwhy!]

I would prefer one or two 3-speed switches, that allow you to use a maximum of 9 different combinations for front|rear motor speed. Having a fast (f)|fast(r) combo would be applicable only for long tarmac stretches to get the highest topspeed. A slow (s) | slow (r) combo would be practical for very technical trails. A slow (f) | fast (r) combo would be appropriate for some average riding, whereas an intermediate (f) | fast (r) combo could be used for steep hills. I don't see any uses for a fast (f) | slow (r) combo.

The switches could work well, but you will also need away of removing the drive from either the front or rear at anytime , as a spinning wheel means no traction, and traction is a very important in trials.

[betarambo]

Wow. As always ES comes through with lots of good stuff. Thanks guys!

by gwhy! » Wed Sep 19, 2012 1:53 am

Yes, should be pretty easy to do a POC with a gas bike with a hub on the front ( lots of video please, while you are getting used to it ),

I promise to get some video of the first rides. I expect I will need to apply some pilot lubricant (beer) to get the controls to make sense! I guess the handlebars will have two throttles, one clutch and a front brake plus the feet will have the rear brake and the shifter. Depending on the amount of pilot lubricant and my adaptability my video might go viral.

hjns » Wed Sep 19, 2012 3:31 am

Nice idea. I would put little less power in the front. Something like a 9C 2807 in front and a cromotor in the rear. For driving slowly and getting enough power, go for at least 18FET 4110 and preferably larger in the rear. You may end up with something like 6-8kW in the rear and 2-4kW in front

Thanks for throwing out actual numbers. I am thinking I might use a Magic Pie 3 in the front becasue I am used to those and the 3 is so very nice for running beefy phase wires. I am running my kid's bike at about 3 kw right now with no issues. I looked at the cromotor last night for a while and it looks promising.

by Bluefang » Wed Sep 19, 2012 6:45 am

An idea would be to use John from CRs hub in the rear. thats good for 6kw+ right out of the box and you can run a really fat 10" off road scooter tire viewtopic.php?f=31&t=40859

For the front wheel i would think a hub with a really slow wind would be a good idea as you would be best running up to 100V and the higher torque of the slow wound motor would be more useful in a large front wheel. FYI a 26" bike rim JUST fits on a 21" front motorbike hub and spoke setup so i would think you could mount a 21" motorbike rim on the spokes from a 26" hub. They did testing on 2wd motorbikes and found that the front wheel only needed a max of somthing like 20% of the rear wheels power and to make a difference it only needed 5%.

Cool ideas, but I am pretty well limited on tires. Trials tires for motorcycles are very specialized. They are super soft and we tend to run them at 4 psi. I would think that a trials tire might last for 100 miles on the pavement, that's how crazy soft they are. They are even tubeless and require a certain rim designed for tubeless. As far as I know, trials is the only offroad discipline that uses tubeless regularly. So this gives me two common options. For the rear I can use 18"X4" and the front we use 21"X2.75". Keeping in mind that motorcycles talk about rim diameter, not tire diamter, the rear is 26" and the front is 27". The only other option I can see is a 19" trials tire they make for enduro guys who ride very hardcore stuff, but I suspect it is still 26" diamter with a little less sidewall. That might be the way to go for the front as the smaller sidewall might be helpful. If I try any other tire I won't get the traction I need. If I go any smaller it will make obstacles harder to clear. This bike will never see pavement.

I was thinking Pie in front and Cromotor in rear. The Croatia folks are working on a motor that is like a bigger pie that might make a better choice for the front or even both ends. For these low speed torque situations you want large diameter motors and small diameter tires.

Cooling may be the problem, make sure to have temperature sensors in the motors.

Pie front, cromotor rear is starting to sound like a winner. If I find I am under powered or overheating I can always swap the cromotor to the front and put an EnerTrac on the rear. That would free up the pie for something stupid like the motorized, rideable, remote control beer cooler I always wanted to build.

The heat issue is an interesting one. On the one hand, we don't go fast so cooling is limited. On the other hand, trials competitions have a good percentage of time walking the sections to find the right line and waiting for your turn to ride so the duty cycle is nowhere near like commuting or something. On my third hand, during practice there can be a lot of slow speed power use without much rest. With my kid's bike we overheated at first. I put some vents in the covers and we have had no problems at all since then. I only put about half of the vents that most people do in hopes of avoiding a sctructural problem with the extra shock of trials.

by gwhy! » Wed Sep 19, 2012 9:29 am

away of controlling the 2 motors could be to use something like I have done on my bike a e-clutch lever but use the regular throttle for the rear and use the e-clutch lever for the front power, if nothing else, it will make it interesting to ride

The e-clutch lever could be an interesting option. If I want to get really silly I could think about using the throttle for both controllers but using the "clutch" to define the power split. Maybe something like out = rear only and in = front and rear 100%. But, it would probably be better to use just as a front throttle. Is this something you bought or something you made? If you bought it, can you point me at a vendor?

Speaking of that throttle, I have been thinking about dual throttles with one on each side. The transition might be easier with something to allow more "hand hanging on" like a thumb throttle or a half throttle. Maybe a half throttle on each side would allow control but also a decent grip on the bars for big obstacles. What do you think?

by hjns » Wed Sep 19, 2012 10:14 am

I would prefer one or two 3-speed switches, that allow you to use a maximum of 9 different combinations for front|rear motor speed. Having a fast (f)|fast(r) combo would be applicable only for long tarmac stretches to get the highest topspeed. A slow (s) | slow (r) combo would be practical for very technical trails. A slow (f) | fast (r) combo would be appropriate for some average riding, whereas an intermediate (f) | fast (r) combo could be used for steep hills. I don't see any uses for a fast (f) | slow (r) combo.

That sounds great. Especially during POC when I won't really know what I want until I get it. I could even change the programming on the front controller as I hone in on what works for what situations. I wonder if I can program the controllers so that speed 1 = 0% so that it could be the disconnect. Then again, it would be easy enough to hook a switch to each throttle to disable it.

It is too bad that the current version of trials rules disallow backing up. Adding in a reverse switch could really open up more possibilities that the gas boys don't get. I think I will have to do that anyway just for some fun tricks.

So, it looks like I should order me up another pie and get this party started.

[gwhy!]

the e-clutch is home made , but it is very simple. I could give you the details if interested.
it can be seen in this thread near the bottom of the page viewtopic.php?f=12&t=32042&start=90

[hjns]

Theoretically you could even have one setting in the 3-way speed switch act as reverse. However, accidentally flipping that at 30mph would result in someone doing a superman. I think it will be easy to have one setting act as zero. With a DD hubmonster you would have significant drag because of the nature of DD motors. Therefore, you should consider having the lowest setting at 20 or 30%.

[betarambo]

Good points.

1. Put some sort of fail safe on the reverse switch. That could get ugly on pilot and machine if it is hit at the wrong time. Maybe a breath-alyzer so that you can't engage the reverse function if you are not sufficiently lubricated? On a serious note maybe a simple circuit using one hall to not engage reverse unless speed = 0 would be good.
2. Good tip. I hadn't considered the drag on the front when not powered. That could really hose you in a tight turn on loose surfaces. Even in high traction situations that drag could create an odd dynamic. I will keep that in mind as I experiment.

[betarambo]

Gwhy, thanks for the link. The clutch sounds very interesting. I had been looking for your build thread but somehow never found it. I know what I will be reading tonight! You should put that link in your signature.

Cool stuff.