MP3 For Childs Motorcycle

[betarambo]

Please help a gasoline and motorcycle guy learn the bicycle and electric world! If I can't figure this out I might have to follow everyone else and switch my kid to a gasoline bike. 
She and I both love the electric bike thing for the low noise, light weight and ease of maintenance.
My daughter has been riding an electric trials motorcycle for a few years now and is ready for an upgrade. Her current motor is rated for 24V and 600W and uses a chain to the the rear wheel. I run it on Lipos with 9s for around 36V and draw a peak of 42A which gives maybe 1500 watts of peak power. I am considering trying the MP III with a 20" cast wheel. I would run it on 12-15 cells of lipo.
The hub motor looks like a really slick way to do things but reading some of the posts it sounds like it is focused more on speed and less on power off the line. For our sport, speed is not much of an issue, but you do need a lot of power from a dead stop. My daughter weighs about 60 pounds and her current bike is 52 pounds with batteries. Any thoughts on how this motor might compare to her existing setup? Details of her current bike can be found at www.osetbikes.com. She has the 16" 24V model although we run it at higher voltage.
I am wondering how much flexibility the software will give me with the controller. Can I change the curves to have it hit max power at very low RPM?
While the 20" wheel will work at first as I can fit it with a Maxxis Creepy Crawler trails bike tire, I would eventually want to change it for a 14" motorcycle rear wheel (this gives you a tire about an inch bigger than a bicycle 20") so that I can get a wider tire for better traction in the loose stuff. It appears that all bicycles are 36 spoke, but adult trials motorcycles are 32 and children's trials motorcycles are 28 spoke. I am thinking that I could either:
A: Lace up the MP3 to a 28 spoke wheel by skipping one hole every quarter of the way around the wheel. This sounds kind of sketchy but maybe it would work.
B: Take the MP III to a machinist and have new holes punched for a 28 spoke pattern. This could be challenging to hit the holes in the right place and not overlap the old holes.
With either option, the spokes would be pretty darn short so it might be kind of tough anyway.
Any thoughts or connections to a US -based dealer would be appreciated. I am located in New Mexico, USA.

[Bikemad]

Hi andto the forum.

I'm not sure the MPIII's controller will deliver enough amps to provide the amount of torque that you are looking for.
On the brief testing I've carried out with my MPIII, it has only delivered around 27Amps @ 31.15V under maximum load.

I think it might be necessary to rewire an MPIII to attach an external controller that can supply at least 50 Amps to provide a decent amount of torque suitable for trials use.

I think that trying to lace a motorcycle rim onto the MPIII will be a bit of a challenge, and I would forget any ideas of leaving out a spoke every 90 degrees.

Although you can purchase 14" rims with 36 holes, I still think you would have serious problems lacing it to a MPIII hub due to very short spokes combined with the narrow distance between the spoke flanges and the unorthodox spacing of the spoke holes:

   

The 20" Pies will accept 16" motorcycle tyres:


But the 10% increase in diameter will also reduce the actual driving force by 10% too.
Check out this post for more details on tyre sizes.

Check out the dealer list to find your nearest dealer.

Alan
 

[truly_bent]

Have you already purchased the MP III? I'm not gonna win any Brownie Points from GM for suggesting this but, If you haven't, then why not an MP II with external 3rd party controller, capable of delivering the higher amp load you apparently need?

When I was planning my setup, I thought perhaps I would need to run at a higher voltage than the GM controller was capable of (i hear talk of a new higher voltage controller coming out soon). Admittedly, mine was a speed issue (volts), while yours is a torque thing (amps), but the controller I ended up buying is way overrated for the MP motor. The motor is rated at 30A while this controller is rated at 65A and has to be software limited to match.

As it turns out, i'm pretty happy with my setup running 48V and 30A and i'm a damn sight heavier that your daughter. I'm thinking that a 60 pound kid at greater than 1440 watts is gonna be more like a launch. But then, maybe trials riders need to climb trees from a dead stop or some such.

If you're interested in following up on this, visit http://lyen.com/ and let Edward know what you need. It'll be more expensive than the MP controller, and a tad more complicated to setup perhaps, but you'll end up with a controller tailored to your needs.

[betarambo]

Thanks for all the help so far! I am learning in leaps and bounds.

On the wheel thing, yes I am becoming convinced that the 14" motorcycle wheel is just too close in diameter to the motor. I emailed with John Holmes at Holmes Hobby. He has done some really cool wheel builds including a bicycle hub motor to 16" motorcycle wheel.
http://www.holmeshobbies.com/blog/?page_id=212
He was very helpful. I measured the hub at 12" outer diameter and the inside of the rim at 13". This leaves half an inch for spokes and the angle would be very steep.

Bikemad, I thought I had searched everywhere for a 36 hole 14" wheel and could not find one. Thanks for the link! Apparently my search skills need some work too. I may come back to that idea later as for trials, the 14" tire is the only true rear until you get up to 17" and 17" is too big for this bike and for my daughter.

So I am on to my backup plan. I need to find the 20" cast wheel that bolts to the MP3. I am having a hard time finding it except as part of the kit which I already have. Anyone want to sell me one or send me a link? You could sell me a tire and disc brake too!
I would then wrap a 20" Maxis Creepy Crawler around it. This isn't perfect as bicycle rubber is a bit too narrow for some of the soft stuff we ride, but it is better than the 16" bicycle tire she has now.

Maybe down the road I will look at upgrading to the 16" motorcycle wheel. Vee Rubber makes a 16" trials tire that they say is front or rear, but it looks like more front than anything.

So to keep my head straight and provide some data for anyone following this silly path who finds this thread in the future:

14" Motorcycle rim and tire: Rim inner diameter 13", Tire diameter 20", width 3" (Cheng Shin trials tire)

20" Bicycle rim and tire: Tire diameter 20.5", width 2" random bike trials tire

16" Motorcycle rim and tire: Tire Diameter 21", width 2" (Cheng Shin trials tire)

20" bicycle rim and 16" motorcycle tire: Same as above, might lace easier than motorcycle wheel but keeping the bead seated at low trials pressures might be challenging

16" bicycle rim with special made for Oset Kenda trials tire: Tire diameter 16", width 2.5" (this one provided for reference as this is her current bike that I want to replace and the rear tire does not find enough traction)

So given the above and my timeline (youth nationals in Colorado are July 22 and I want to have her new sled ready and have her used to it by then), I will go with the sure to work solution and get the cast 20" rim.

I got the MP3 yesterday. I threw it on an old rigid mountain bike for some testing. The guy who sold it to me said it would be configured to run at 24, 36 or 48 volts. He said he was having a hard time getting the programming cable to adjust this.

I hooked it up to 24V first and got nothing. I switched to 48V and it worked fine. I rode it around a bit and it felt similar to her Oset. In testing on the hill in my driveway I found that it was slightly slower up the hill from a dead start at 48V than the Oset at 36V, but barely. Both tests had me as the pilot.

I had her get on the Oset and we raced. As expected she blew me away up the hill since she weighs about 1/4 what I do. Once we got on the road I had maybe 30% more top end.

My hope is to get by with the stock controller for a couple of months. This assumes that I can get one of the programming cables and dig up a machine running XP so I can tweak some things. After that I will look at buying a good external controller that will allow me to keep bumping up the power as she gets better. From what I have read, I am thinking a Lyen 12 FET controller, which would be overkill but would give me options in a couple of years when I build the next bigger one for her. Opinions here are very welcome.

It may be that rather than messing with the cable I should jsut go straight to the external controller. I guess if I have to install and figure out one software package I might as well do the one that will work long term. Any opinions on the ease of setup for Lyens versus MP software? I was a programmer and I am still a computer guy, but my skills are maybe rusty.

One big advantage is that the throttle response is not so jerky. The biggest problem the Oset has is that it puts down so much toque from a standstill that she spins a lot. I think the controller has a lot to do with it. By my way of thinking, it isn't torque directly that breaks traction or even acceleration. I think it is jerk (acceleration change over time) which is all in how the controller ramps up. Then again it might just be a lack of torque.

The testing was done on the random 26" wheel that it came with so I expect better performance on the 20"

I live in New Mexico so I have no local dealer who is into this stuff as far as I can tell. The local bike shop wasn't much interested in selling me a brake disc or even a spoke wrench, so Internet shopping it is. I was kind of bummed as I wanted to support the local mom and pop shop, but I guess not. Anyone looking for a customer please let me know.

[betarambo]

One issue I didn't see coming is the swingarm and how to mount the MP. I read someone on a thread on here talking about it and realized I need to solve it.

The problem is that a bicycle has a notch to drop the axle in. A motorcycle has a hole to slide the axle through. In reading about the need for torque arms I think I will probably kill two birds with one stone. I figure I will lop off the end of the siwngarm to make the O shaped opening in the back become a U. The U opening will be a bit too big for the axle. I will have a sleeve machined to fit the axle inside it and have it slide into the U on the swingarm nice and tight. I need to work out some details of clamping it down nd whatnot but this sounds like the simplest solution. Thoughts?

[truly_bent]

Ummm...
Need visual aids to follow that one. Can you post a sketch or annotated pics to help?

[Morgen 3Eman]

If the metal you cut into the U is 3/16' or less, the torque generated by the MP3 can bend the slot open.  And then the axle loosens.  And then the rear end of your vehicle gets hard to control.  Want  to guess how I know? 

I suggest you put some hefty metal into what ever use use to resist the torque. (You could  just weld some plate onto the side of the cutout.)

TTNF,
Dennis

[betarambo]

http://www.flickr.com/photos/80256401@N03/7185417395/

The swingarm is 3/8" thick aluminum where the axle goes through. Hopefully in this picture you can see the O opening I was talking
about. I would cut the end off to make it a U so I can slide the axle in. The opening is a bit too wide to hold the axle. By hand it lets it rotate about 30 degrees before catching so I clearly need to add some material to hold it nice and tight and steady.
 
Couldn't remember how to embed an image. Couldn't find the thread about it.
 
Thanks!

[Morgen 3Eman]

The flat on the MP3 is about 10mm, and I'm guessing your axle opening is about 17 mm or so.  One thing you could do is bend a 2-3mm thick 3/8" wide steel strip  into a shape that fits snug inside your swing arm opening, and snug around your axle, then bond it into place with some high strength  epoxy.  The steel would greatly increase the alloy's resistance to bending open.   You absolutely do not want to have any slop between the three pieces for the axle to rotate in.  At low speeds, the pulse width modulation effectively hammers the rotor with a max power torque pulse a couple of times a second.   

I'm sure there are many other ways to accomplish the same end, and there are torque arms offered for sale that may be suitable for your swing arm.

TTFN,
Dennis

[Bikemad]

Your aluminium swinging arm would be considerably weakened if you cut of the rear section to slide the wheel in, and I'm also guessing that the distance between the two mounting points will be wider than the usual 135mm for a rear Pie.

You might be able to fabricate (or have fabricated) some steel adapter plates that could simply bolt on to the swinging arm to allow the wheel to be mounted either below or above the existing axle fixing point as I've shown here:


A 4" smaller diameter wheel fitted 2" below the existing axle mounting should produce far more torque but still have the same ground clearance.

If the plates were thick enough they could be threaded to accept the bolts, or weld some nuts on the back instead.
You might need to use some spacers where the bolts pass through the slots to eliminate any movement, unless you use bolts with a very large diameter thread.

Alan
 

[truly_bent]

Bikemad;
That's a truly slick solution. Love the CAD effort.

However, this part I don't follow:

A 4" smaller diameter wheel fitted 2" below the existing axle mounting should produce far more torque but still have the same ground clearance.

I know it's not my problem, but I am curious. Could you elaborate?
Thanks

[Bikemad]

I find it generally causes less confusion to draw a simple diagram, rather than try to explain things by using text alone.
I don't know if I've confused you over the ground clearance issue, or whether it was the misuse of the the word torque, so I'll try and clarify both points:

Let's assume that a 20" wheel has a 10" radius and a 16" wheel has a 8" radius.

Fitting 16" wheels to a bike designed for a 20" wheels would bring the frame 2" nearer to the ground, thereby reducing the ground clearance by 2".
Using adapter plates to locate the axle 2" lower than the original axle position would compensate for the smaller radius of the wheel and ensure that the ground clearance remained exactly the same.

Perhaps I should have said "far more driving force" instead of "far more torque" as in reality the actual "torque" is governed by the motor, and would be exactly the same (relative to the wheel rpm) regardless of the wheel size.

If Torque = Force x Distance, then Force = Torque/Distance, so reducing the distance (the radius of the wheel) would increase the force available at the road for any given torque.

If the wheels were fitted with identical motors, the 16" wheel would produce 25% more directional force (relative to the wheel rpm) than the 20" wheel, but the top speed would also be reduced by around 20%.

Hope that's clarified things for you.

Alan
 

[Morgen 3Eman]

Alan's solution is brilliant. It could even be used to change the wheelbase depending on the layout of the course. 


Regarding the CAD work, I think he is just showing off......


TTFN,
Dennis

[truly_bent]

Ha!
Bikemad; Your clarification has helped to, er... clarify that. Thanks.

Just to confuse the issue; since the 16" and 20" MP windings are configured differently (one Wye, the other Delta), which configuration would be better for the low end torque Rambo's looking for?

The answer is moot now anyway, since he's already received his wheel, but maybe for the next guy.

[betarambo]

Bikemad, thanks for spending time to illistrate the idea. I love forums like this where the community will chip in to help some random noob out.

I keep going back and forth on the actual wheel I am going to use between 20" bicycle (actually a 19" trials bicycle) rimwith Creepy Crawler 20X2.5 trials tire or 14" motorcycle wheel with Vee Rubber 14X3.00 tire. The motorcycle tire is the way I want to go since it is wider and a little shorter. I think I am going to get that to work but it will end up using the shortest spokes in the history of spokeness.

Anyway, if I use that wheel, it is the wheel and tire from the donor bike so ground clearance and seat height for my daughter would be unchanged if I can fit it in the stock slots.

You are right that lopping off the ends will significantly weaken the openings and allow them to spread if pushed hard enough. I think my plan would be to build an adapter for each side to clamp tightly onto the flat spot on the axle and then tightly fit into the slot. If I spend a little mock up time I should be able to repair the structural loss with some sort of clamping force on the notch.

Luckily I do have access to a machine shop at work and I have been buttering up the machinsit for a few months in anticipation of this project.

The swingarm width is actually fine for the MP3 since the swingarm is from a kid's motorcycle so it is smaller than normal.

The idea of those brackets sure is temping though. If I designed it with enough thought, I could use only one, very large, bolt through the old axle hole and then have the second bolt have a couple of options about whre it bolts. This would allow the bracket to rotate for adjsutment of wheelbase and ride height. If I got it rotate around the ned of the swingarm I could even reduce clearance by mounting it upside down from the awesome drawing.

I am thinking that I might be getting complicated just for the sake of fun design. I am heading out to the shop now to tinker around and see what shakes out.

The plate idea sure is intriguing...


Thanks guys!