Gruber
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M.L. Toys
KidsWheels
Gruber
HobbyMasters
M.L. Toys
KidsWheels
HobbyMasters M.L. Toys
Gruber
KidsWheels
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By bpsims
#147591
After over-volting the stock motors and completely destroying the plastic tires, it was time to start modifying. I wanted parts that could be moved on to other projects when the time comes so this is admittedly a little overkill for a power wheels. We're in the shake down process now - still a lot of little things to do - but it's performing pretty well.

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48V 1000 watt scooter motor
48V controller
Hydraulic disc brake
1" solid axle keyed w/ pillow block bearings
11 tooth / 84 tooth sprockets
#35 chain
6S Lipo 12ah batteries x2
15x6.00-6 wheels x4
Front go kart spindles

There were a lot of missteps on my part during the build that added to the cost and time but what we ended up with is pretty stout. I have a 48v 1000 watt ebike which drove my decision for the motor. I'm familiar with the power and having a second equally sized battery pack was a bonus (these aren't exactly cheap).

The metal frame of the Dune Racer was a huge help in putting all this together and it's surprisingly sturdy. The motor and controller are from awful sellers on ebay.

After stripping the plastics from the rear, I welded a mount to the frame to hold the motor.
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Slots in the mount didn't adjust chain tension much since the chain runs vertically from the axle to the motor. Almost all of the chain tension adjustments now come from stacked washers under the motor plate. A nice surprise - the 1" pillow block bearings mounted to the stock holes in the frame!

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The sprockets were probably the most frustrating/infuriating part of this project. Hours and hours were lost in trying to find some compatibility between axle and motor. Almost all of these cheap ebay scooter motors come with an 8mm or T8F chain sized sprocket. Finding a large 8mm axle sprocket is next to impossible. Crazy that there isn't an aftermarket for this.

I gave up on the 8mm and went with #35 chain and sprockets which have all kinds of options. But this required some work to get it to fit the shaft of the motor. The motor has a "double D" (2 flat sides) 12mm shaft. A #35 sprocket with 3/8" bore drilled out with a 15/32" bit fits well (tight - took some heat and encouragement). Crank down the set screws with some loctite and it's holding well.

My first sprocket combo was a 9 tooth motor sprocket paired to a 72 tooth axle sprocket that, with 15" tires, gave me a 15mph top speed with lots of low end grunt. But, that small 9 tooth sprocket came with a lot of Chordal Action noise. It was loud! I'm now running an 11 tooth motor sprocket and a (huge) 84 tooth axle sprocket with a top speed of nearly 17mph. A little too fast so there's a screw acting as a governor in the pedal. But it is noticeably quieter.

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I wanted disc brakes for a number of reasons. The idea of shorting this motor through some resistors never felt like the right way to approach stopping. We have other big kid go-kart toys that use disc brakes and I wanted my son to start learning how they work/feel now. Plus, it's fairly easy to setup.

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The solid axle brings the obvious steering issues. I have a locking differential plan that's coming but for now, I needed to address the front end plastic steering components. I cut off a bit of frame to hold new 3/4" spindles which are mounted with about 12 degrees of positive caster. New threaded rod and heim joints were connected up for a much more stout steering solution. We're still using the stock steering shaft. There's still a lot of understeer but we can make a full turn in the space of a residential street. It can be a little tighter of a radius depending on speed. There's not a lot of space to fit all the steering bits and the brake parts but it performs well - considering this is the first time I've ever attempted something like this lol.

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The little compartment up front holds the controller, master cylinder reservoir, and batteries. Barely. This needs more work. The controller is getting very hot and I don't like it that close to my batteries. I also have a 48v to 12v converter that needs mounting somewhere. The controller is connected directly to the stock gear shifter that I rewired to handle reverse duty as well. No relays and it's working fine. If I can find some relays that don't cost a small fortune I might try them. But for now, it's all good.

Future:
The accelerator pedal is really twitchy. Getting going can be really jerky if you don't manage the pedal well. As the torque moves you forward, your foot falls away from the pedal a bit which slows it down. You correct with more throttle and then the whole cycle repeats. I'm looking for either a larger, smoother (stiffer?) pedal or some sort of electronic solution to this. Seems like a lot of stress on the drivetrain.

I have an idea for a locking axle and the parts. It'll require splitting the solid axle in half and then adding a hub on each end where they meet which can then be coupled together when needed. It'd be nice to have this thing perform on the street as well as it does in the dirt.

I'd like to work on the gearing. More low end and bring the top speed down. But the sprocket size starts getting ridiculous - it's almost the size of the tire now. I'll most likely have to go to a geared motor to get a reasonably sized axle sprocket on there.

Some of our shake down test drive:
https://youtu.be/IZIvGOHLTt8
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