Build: Youth Electric Trials Motorcycle, MP3

betarambo

10 W
Joined
Jun 12, 2012
Messages
68
Location
New Mexico, USA
I guess it is time to start the big write up so here goes:

Why

I ride moto-trials which is a motorcycle sport that is like an obstacle course. Think tight turns, riding over rocks, logs, cars etc. and you are scored based on not putting your foot down and not going out of bounds. My daughter started riding when she was one year old on a Yamaha PW50 with training wheels.

As she progressed the flaws in a gas engine for kids became apparent.

1. The governor is challenging on a gas bike. They do it with a combination of blocking exhaust and limiting throttle. You end up with limiting it so much that they can't do hills or leaving it too open so they go too fast. The automatic transmission adds to this problem as it takes a lot of motor RPM to get the transmission going. On top of this you get the scary noise and the potential burns from hot parts.
Hannah pw50.jpg
2. Then Oset came around. They are the #1 electric motorcycle manufacturer in the world these days (I think). They make these awesome bikes for kids. The bikes are very small (the little one has 12.5" bicycle wheels and the big one has 16"). The cool thing is that you control speed by a reostat and it is very controlable.
Hannah on Oset.JPG
3. Then she grew taller. Oset talked about making a 20" bike. I think they will but the deadline kleeps slipping and she keeps growing. I ditched to training wheels and bought a stem and bars to make it bigger. I converted it from sealed lead acid batteries (SLA) to Lipos. I ran it at 36V instead of the 24V her bike was made for. In the end though, the bike is too small and the 20" Oset is too far out. They recently got some competition and I fear that this is driving them in directions other than finishing the new, bigger bike.
View attachment Hannah learning to wheelie.MOV
 
So, what to do? I decided to build her a bigger bike based on a ten year old Gas Gas 50 and a Magic Pie 3.
Her current ride:
hannah on oset.JPG
The donor bike:hannah on gas gas.JPG
The Oset weighed in at 52 pounds with batteries. The Gas Gas was 101 pounds with no gas. No wonder Oset is so cool. My 60 pound kid riding a 101 pound bike is like me riding a 400 pound bike! My goal (mixing reality with theory) is 80 pounds for the new bike.
The new bike is almost done:
sparky on stand.JPG
 
More to come, time for bed. :D
Issues handled:
1. How to get a motorcycle rim (14") on the pie.
2. How to get a valve stem so I could put air in the wheel.
3. How to mount the wheel to a motorcycle swingarm and not have torque arm issues.
4. How to make the 10 year old plastic look ok. (the plastic is older than Hannah is)
5. How to mount the batteries to be safe using lipos, allow future expansion, and make it look good.
6. How to get the wieght down (85 pounds right now with batteries, hoping to still get to 80)
7. How to get enough power for trials but avoid the tire spinning that the Oset shows from a dead stop.
8. How to avoid getting divorced while I obsess about this project, putting in 4 hours average every night during the week and lots more on weekends for 2 motnhs.
9. How to get a disc brake on the motrocycle swingarm with a MP3.
Sparky.JPG
 
Very nice work!
What decided you to use a hub motor? I fear the weigth in the rear wheel will be hard to lift over objects (I do some trial riding myself) But at lest this frees a lot of frame space. I would have used a frame mounted motor or a geared hubbie but that frame looks very small. The motor should have a lot of wheelie power but she indeed needs a rear brake ;) I dont know if you plan to do that, but on commercial electric bikes (electric-motion) they use a fake clutch lever that actually works as a second throttle, it helps to prevent death grip and gives more control on tight maneuvers. I use a left side rear brake on my bike and it's very nice for control too, but you may want to have a control setup similar to the gas bike for the future!

Adam
 
Perfect except for the hub weight. Right motor, right rim size, and so simple. Be a blink of an eye till she can ride 125 size stuff anyway, so not so worth it to go chain drive and have to fabricate so much stuff.

So she learns to handle a heavy back wheel, and has a skill advantage later when she goes back to more weight low and center.

You are the guy in Lost Chances right? Let us know when you compete or just ride local, I'd love to get some film of her on it.
 
The hub dont look out of place but I bet it makes the rear very heavy ( hard to bunny hop ) when she gets to that stage. Is the swing arm on the GG50 the same width ( at the pivot ) as a full size gg ?, if is is then the setup I am using on the sherco conversion will also fit into the 50 like this here http://endless-sphere.com/forums/viewtopic.php?f=12&t=32042&start=60.
 
For the bake brake I have a large bicycle disc (203 mm) and a cable operated caliper. It is almost done but I still need to fabricate a mount. Hoping to make progress on that tonight.

The hub weight is indeed the most interesting part. For right now she doesn't do anything that requires the wheel to leave the ground but she will soon. I want to see how it goes. It does indeed make wheelies way easy which is the skill she needs most right now for obstacles. If it comes down to it I am prepared to switch to a more conventional aproach and put a chain back on it. I just love the simplicity of no chain. Also, all that wieght is centered on the rear axle which is at the level of the bottom of the skid plate in normal conditions. This means I effectively lowered the center of gravity of the bike a few inches which should be noticable for balance.
dogman said:
You are the guy in Lost Chances right? Let us know when you compete or just ride local, I'd love to get some film of her on it.
I am in the Albuquerque area. We will have our next local trials in Taos in two weeks. Come on up and join us!
 
So the bike works now! I am on my second motor and fourth controller but boy is it slick. My kid is loving it.

The issue of all that weight in the back wheel did indeed have the positive effect I had hoped for. It puts the center of gravity so low that she can balance on it at a dead stop much better than she could on the Oset. Tonight she did about 15 seconds of no motion balancing right away. I will see if I can post a video of it.

The issue of unsprung weight limiting bunny hops is still up in air as she isn't trying that yet and I am afraid to break the bike with my considerable mass. :)
View attachment 1
The setup now is a Magic Pie II with a Lyen 12 Fet controller. I run it on two or four lipos for either 12S1P or 12S2P depending on the range we want. Right now we are getting about 2,000 watts from 50V and 40A. This gives me a lot of head room to add power as her skills increase. For now that is plenty of power for her. She really likes how it has plenty of torque and speed but isn't as abrubt on take off as the Oset.

I finnally tracked down some Vee Rubber rear 14" tires that are way soft compared to the crappy old Cheng Shins. It appears to have very good traction with the tire/motor/controller combination. That was a big issue on the Oset with the little 16" bicycle tires.

We ran the MP2 on the stock internal controller for a weekend. It had workable power but overheated a fair bit. It would shut down on us. If you disconnected power and re-applied it, it would give 6 beeps to indicate overheat. After about 5-10 minutes of sitting it would run again.

I expect to have no problems with that now as I ditched the internal controller and venter the hub motor. The new controller is mounted up front where the radiator used to be to get good air flow. For vents I didn't think I needed a ton with only pushing 2kW, but I do need some since trials is pretty slow. Also, I was concerned about the structural rigidity of the covers as trials tends to put a lot of shock into the bike. I ended up going with 6 slots near the axle for intake and 6 holes on the perimiter for exhaust. I angled the edges of the slots and holes into the flow on intake and away on exhaust. I think I ended up with a pretty nice compromise between venting and structure. I did the same pattern on both sides. I considered the idea from another thread on here of using fan blades internally and doing intake on one side and exhaust on the other. I decided I didn't need to go that far at these modest power levels. Also, the riding we do is so slow I am not sure the centrifugal fan idea will really flow much. I think the main gain I get is just letting some hot air out and some cool air in which is a heck of lot better than leaving it sealed.

I got the bake brake all working. Even with me on it and moving fast I can lock up the rear tire. I fabricated a mount from an aluminum plate. The key was buying a caliper with an adjustable mount to get everything all squared up. The MP3 was a lot easier to mount the brake disc on the the MP2. The MP2 is wider so you can ahve a lot more issues with the caliper hitting the motor case. I ended up using disc shims plus cutting an old disc to use its inner diamter as a spacer to get the disc far anough aware from the motor. Even with that I have 1/32" clearance from the caliper to the motor side cover. I hooked it to a hand lever on the left side of the bars so she has two brakes on the bars, but reversed from how a bicycle does (moto style). If we ever decide she will trnasition to a gas bike I will probably hook it up in paralell with a foot pedal so she can get sued to that. For now the plan is for me to keep learning and keep building her bigger e-trials bikes as she gets bigger. She says she wants to stay electric. It might make it harder to get sponsors when she gets to that level, but it will keep me from getting bored in the garage!

I am very excited to finally have it working and so is my kid. Tonight after dinner she immeadiately asked if she could go ride some more. We went through about 10 aH before it got too dark to ride any more. I am sure glad I bought so many lipos as I think she is going to be going through em!

Thanks to everyone who helped. Just about anyone who ever posted here helped. Lyen gave me some very good tech support. Dave at DG Green Products http://www.dggreenproducts.com/ stood behind his sale and really stepped up on warranty. He is also the guy who made the super short spokes with a spoke machine that he modified (they are less than an inch long). Stevie of Stevie's Happy Bikes here in Albuquerque was the only bike shop in town willing to help with the wheel. He did a great job truing up the wheel once I got it strung (twice) and charges like its the 1950's.

I will try to start paying it back by posting the various solutions that I found to the problems so maybe someone else can get some help out of it. I took a ton of pictures along the way for that purpose.

:D :D :D :D :D
Sparky Lakefork1.jpg
 
Balancing on the new bike (assuming I can post a video).
[youtube]uRj5o2mNdmM[/youtube]
Test ride in the yard:
[youtube]CyhqUuu6t7w[/youtube]

:D
 
Nice job on the bike! I would love to see a video of it but the huge .mov attachment didn't work for me.

You need to upload the video to YouTube and then use the YouTube button on the right when composing a message and insert the unique ID portion of the URL in the middle of the command... It's Easier than it sounds but try it and you'll see.
 
Thanks for the tip. I sure am learning a lot on this project. Wheelbuilding, battery tech, plastic fabrication, motor control theory, and now even my first youtube videos.

As you can see, your tip got me going.

The bike really is a blast. Once I got to testing it I didn't want to get off of it. I finally had to as I couldn't bear the thought of breaking it when it is designed for 1/4 of my weight!
 
Better video to show how this bike will really be used. In competition she will ride more obstacles and tighter turns, but you get the point, this is a slow sport so heat could end up being an issue even at only 2 kW.
Picture of the intake vents:

[youtube]R3DLVdEdEQA[/youtube]
[youtube]8z0KyNC-1lo[/youtube]
 
HaHa!
Totes Awesome betarambo, sweet looking build, fantastic that you've got your girl mixing it up on it... Big props to the pair of you :)

joe
 
Good job getting it finished, this will make a very good trainer bike with scalable power! Liked the no motion balance, your daughter already got some good skills!
How did you setup the brakes? Left hand rear brake I suppose?

Adam
 
betarambo said:
Better video to show how this bike will really be used. In competition she will ride more obstacles and tighter turns, but you get the point, this is a slow sport so heat could end up being an issue even at only 2 kW.
Picture of the intake vents:

[youtube]R3DLVdEdEQA[/youtube]
[youtube]8z0KyNC-1lo[/youtube]

Good stuff! Last YouTube tip. Never record videos in portrait mode. You're losing 2/3rds of your video to thick black bars. Landscape is the way to go!

Your daughter is very lucky to have such a capable dad!
 
Wow. This bike is fun and so is youtube. She rode for two hours straight today. Went through two sets of 12s2p 48V 10 aH. She gets better everyday. Check out my fun montage of the bike in action. I learned not to let yourube take the shaking out of my video as that causes those odd moments when she shrinks and grows.

[youtube]hXDMabBV5JI[/youtube]
 
Very nice build betarambo, it handles like a "real" trials bike. So much better than the Beta Mini.
Do they use the same Franco Morini engine with expansion pipe in the Gas Gas ?
 
Thanks. I think the engine was actually a Gas Gas but it did have an enormous expansion pipe. Those motors never ran very well for anyone. That's one of the things that made it a nice donor bike.

So we started at 48V and then went to 60 a few weeks later. Last night we went to 72V. It is awesome! This bike is so fun I want one for myself. We are now running 18s2p to get 72V 10 aH. I am starting to look at a BMS and changing my Zippy ipos into packs. When her Oset ran 2 6s1p packs it was pretty easy to keep things charged. Now that we are using 6 packs and I have three sets it is getting to be a pain.

I have three good chargers and a couple of big power supplies so I can charge all three sets in a few hours, but it is pretty annoying. When we are at events I now have a pretty good setup. My camper has 3 gel cells, a generator and an 80 amp supply for charging the house batteries. I butchered a set of jumper cables and made a cable to power up to four chargers at full tilt without the generator running. I use the cable to setup my charging station away from the camper in case something pops.

I am thinking about the psuedo-BMS that Methods sells. I could use that to builkd up packs of 18s2p and then use a bulk charger most of the time. That would help for those times where we do a little riding and use maybe half a pack and then take a break. Right now I pull all the batteries, put fresh ones in and start charging the others. If I was bulk charging (safely with the Methods boards) I could actually top it off without pulling batteries out. I could then balance the batteries once in a while when we are home.

The biggest problem is that I very often charge from the house batteries on the camper. This means that my source is 150 aH of 12V. The bulk chargers I see that can handle 72V packs all want AC so I woul have to run the generator or setup a fairly big inverter. The inverter would work, but it hurts my feelings to be so clunky by converting DC to AC just to convert it back to DC.

Does anyone know of a bulk charger that does a DC step up so I can run it from 12V and charge at 75V?
 
I haven't been on here in a while so I thought it was time for an update.

The bike now has 7 trials competitions on it and lots of practice. We have had zero failures now that the bugs are worked out.

The unsprung wieght issue of using a hub motor appears to be a non-issue. In watching the suspension move when she rides obstacles or jumps it, it appears to work just like normal. She is able to get the back wheel in the air no problem even on flat ground. My conclusion is that the unsprung wieght thing a lot more for normal applications where suspension is used to soak up bumps. In trials we misuse suspension and use it to get the bike in the air to get up rocks and such. Because of this, it doesn't much matter where the weight is as the entire weight of bike and rider must be lifted.

Rotating weight still applies, but she reports plenty of power and the rear brake will lock up at speed even with me on it.

I found out that I was right on the edge of blowing my Lyen's controller by running 72V. When I ordered it I told him I was going to do 48V. I then forgot that he built the controller just for me. He used smaller FETs to reduce the voltage draw and optimized it for 48V. Apparently these FETs would have blown at 75V and I was running like 74.99V hot off the charger. So we went back dont to 60V. She says it has plenty of power so we are content there. WE are getting about 2600W out of it right now. In fact, it had enough power that she actually looped it in a section two months ago!

I did notice some problems the other day when she was repeatedly spinning the rear tire in deep sand. The vents I drilled let some sand in and allowed it to rub. That can't be good for the motor! My thinking is that the overheating we experienced early on was with the controller in the motor. Now that the controller is external I think I will put temporary plugs in the holes. I suspect I will keep crud out and still not overheet. 2600 watts isn't much for this motor so the vents are probably not needed.

She still won't stop growing so I am starting on her next bike. I think I will use the magic pie 3 again but build it on an 80cc donor bike with 17" rear 19" front motorcycle rims. Finding a donor bike is proving really tough, but I wil find a way!

Along the way I set up as an Oset dealer. My second order of bikes is on its way and this one includes my first of the new 20" Osets. I can't wait to check it out. It runs 20" trials bicycle wheels front and back with Creepy Crawlers on them. It has a custom motor and controller and pretty nice looking suspension. It could be that I build one of these up to 24" wheels as her next bigger bike.

Thanks again to everyone for all the advice!
 
I got my first 20" Oset and this thing is awesome! Sparky is now retired and my kid is switched over. It has 5 kW of power but feels like more than that. My buddy looped it in the driveway today even after I warned him about the power. He gave it full throttle and it just shot our from under him. I wish I had video! It reminded me of a video I saw on here when I first joined of some guy (liveforphysics maybe) on some super high powered bike just launching it out from under him and landing on his butt.

I converted it to Lipo today and now it weighs in at 68 pounds. The thing is an absolute kick to ride and is built strong enough for adults. I can't stop riding the thing!

5 kW, suspension adjustable for preload and dampening front and rear, and the cherry on top is that all that comes with a warranty!

The controller is pretty unique. It was designed by Oset specifically for this bike so the power delivery curve is different than a typical design. It hits ahrd off the line if you want it to, but it comes with an adjsutable "powerband" pot. This thing doesn't jsut limit peak current. It limits current over time or something. It is hard to describe but I will try. It softens the hit off the line, but allows full power later. It is almost like it is a current limit that is proportional to speed so that it prevents you from wheelying or spinnign on launch but allows full power at speed.

I have a feeling that some of you out there will find yourselves investigating this controller for your higher powered setups if you go off road.
 
Although I am not into doing trials, I am interested in the Oset and how that compares to the MP3 version you built. I've done a brushless Razor build for my son, but he really needs a bigger sized bike. He's into jumping and regular MX stuff - but he rides in the backyard, so want/need the quiet. There is a guy locally selling a used 20 Oset for $1900 obo. I would get rid of the SLA's day one. Still more than doing a pit bike conversion with a rear hubmotor. I am confused about tire size and what works on using motorcyle rims/axle width and such with a bike motor setup.
Any thoughts?
 
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