M.L. Toys
M.L. Toys
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Need new motors? Grind a gearbox? Adding teeth to a pinion?
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By dfreas
So I finished a 24v conversion of my son's Dune Racer and posted that earlier today. Now I'm on to my daughter's Dune Racer. I've already completed tear down and I have half a dozen layout drawings. With slight modifications to how I built the battery housing under my son's car I think I can fit four batteries - I'm using this fact to increase aH, not voltage so I plan on the final car having a 24v 36aH capacity.

The bigger difference though will be that this one is going to be dual chain drive with 250w scooter motors. Based on my measurements I think I can almost completely hide this in the stock plastic housing with the chain coming out perfectly between two bolts so it looks like part of the fake plastic motor. If it works out like I think it will it will be really cool.

I plan on using the EastCoast Powerup Easy ESC the exact same way I did with my son's car - the only difference will be that in this case I'll hide the acceleration and top speed controls in the back where the stock battery goes. This is purely because I have a 3 year old that can't be trusted with a hall throttle, and no amount of parental oversight is ever going to be enough to keep him from sneaking on the fast power wheel when no one is looking.

Two big questions:
1. Dune Racers have bigger wheels: 15" in the back, so obviously switching to a standard go kart wheel with a sprocket on it would just look stupid. For those of you that have mounted metal sprockets on to stock wheels how did you do it, and what tips do you have? So far the easiest way looks like removing the drive gear from the stock gearbox and bolting that to a metal sprocket, but that means I lose the stock gearbox. I'd kind of rather keep those in a drawer as spares for when my son eventually burns up his. I've also thought about using a PVC closet flange fitted over the outside of the tire attachment, but not sure if I can get that to fit tightly enough. Any ideas here are welcome!

2. Sprocket size recommendations? I have mostly flat grass - we live in a rural area, so virtually no pavement driving is going to happen, but there aren't any big hills either. I'm currently leaning towards something in the 60-70 tooth range, I've got a 66 tooth gear that's my top choice right now. Motors are standard 250w 11 tooth scooter motors. Anything in the 40-50 tooth range will probably make my wife scream at me, but 80 tooth seems like it isn't much faster than a standard 24v conversion with stock motors/gears. How fast can I push two 250w motors before there just isn't enough torque to pull a kid around anymore?

Question #1 is way more important that #2 at this point. If I have to I can always buy three or four different sprockets and try them all - they shouldn't be very difficult to swap out once I have the rest of the build done.

User avatar
By dfreas
Ok, so after going back and forth between about a dozen different sprockets I ended up ordering "Upgrade 65 Tooth Rear Sprocket #25, 4-bolt for Razor E300 electric scooter" off Amazon.

The deciding factor ended up being the bolt spacing and the inner diameter. Plus at 65 it fell within my acceptable range for number of teeth. Assuming I decide to bolt it directly to the stock wheel gear I needed a sprocket with bolt holes somewhere between 1 3/4 and 2 3/4 from center in order to fall within the two raised sections of the gear and give me a nice easy space to bolt on to:
IMG_2666.JPG (62.8 KiB) Viewed 2615 times
I still may not do this - completely open to any suggestions someone on here may have. I'm also considering making a copy of the stock piece out of a schedule 80 flange just so I don't have to sacrifice a stock gearbox. But either way the drive sprocket has been chosen.

I'm hoping that in the final build I can line up the sprocket to be between the two screw holes you can see in the gear box outer housing here:
IMG_2665.JPG (69.33 KiB) Viewed 2615 times
With this sprocket there should be just enough room without having to make any cuts, but if it doesn't line up perfectly I may have to trim out a channel between the two screws. If it fits without cutting then the final build should appear completely stock until someone hits the gas peddle - which I think would be really cool. :D
User avatar
By Hammer-fm
Are you going to put a bearing or bushing inside the gear (it's going to essentially ride on the stock axle, right?) The tension on the chain is going to want to pull it out of alignment with the wheel so it will need some support. It looks like the sprocket itself is pretty thin so there isn't any way for it to do this for you.

I have yet to break any of these (final gears) at the wheel:gear interface. I've had one lose a tooth but not in the last year (ironically all of the highest-powered 4x-775 motor ones have been 100% reliable). The 7R ones seem to be fairly strong.

Definitely interested in seeing how this plays out. It's not a route I'd thought of going but the ability to change the gear ratio easily is appealing, and I like that you're keeping two motors rather than having a single axle with the associated scrub/turning issues.
User avatar
By dfreas
This is exactly the kind of comment I was hoping for! Thanks. That would have been a real bummer to realize after I had the whole thing assembled. Easy fix, but much easier to do it ahead of time than to watch it fail and have to fix it after the fact.

I think I'll probably wait until the gear arrives and I can physically line it up and see how it looks before I make a decision on how to deal with the chain tension issue. I'm leaning towards something like this:

The bolt holes don't quite line up, but I can always drill some if I have to - should be fairly easy to get the holes right if I assemble it all on the axle and mark it. I'll keep looking at various bushing options over the next day or two while I'm waiting for the sprocket to arrive and see if I can find a good solution.

Other option is to just put a bearing inside the gear like you suggested - if I look around long enough I can probably find a 3/4" bore bearing that has the right o.d. to perfectly fit inside that gear - I'll have to go measure what the gear's i.d. is - I didn't check that before.
User avatar
By dfreas
i.d. on the gear is 1 3/8" so it looks like this is a perfect fit: ... 6?fromRR=Y

if I add a washer and a lock collar to hold it all in place and I think I've got a pretty easy fix for the chain tension issue with no drilling. Should also help the wheel spin easier against the inner lock collar, which was another thing I was a bit worried about.
User avatar
By dfreas
Sprockets arrived yesterday so I got them attached:
IMG_2671.JPG (59.08 KiB) Viewed 2454 times
IMG_2670.JPG (53.5 KiB) Viewed 2454 times
The bearings also arrived and they are NOT a perfect fit - about 1/16" too small. I'm going to try some combinations of rubber washers and gaskets to see if I can get something to hold it tight. I'm thinking if I stretch a slip joint washer that is just slightly too small over the bearing it should work.
User avatar
By toycrusher
That all looks great! If you do strip the wheel driver, they are cheap to replace! 8-)
User avatar
By dfreas
The slip joint washer idea worked for fitting the bearings into the wheel driver. I had to grind down the rubber slightly with a bench grinder (VERY carefully!) while maintaining the slight angle so it was all a tight fit:
IMG_2675.JPG (76.48 KiB) Viewed 2327 times
However this only provides about 1/8" of tight contact surface so after that was fit I flipped the assembly over and filled the gap with silicone:
IMG_2676.JPG (67.23 KiB) Viewed 2327 times
Not as solid of a seal as the rubber, but at least it should prevent things from shifting around. After that I locked it all together on the axle. My axle was also not exactly 3/4" - it's off by so little though that it is either metric or maybe just age (expansion/contraction, corrosion?) has changed it ever so slightly. None of my 3/4" fittings would go on unless I hammered them and I wasn't about to hammer a ball bearing into place. So instead I hit it very lightly all around on the fine side of the bench grinder - just enough to make it shiny again - and then spent an hour running 80 grit sandpaper over it until everything slid on smoothly.

Did a test fit to see how everything is going to line up and so far it looks perfect:
IMG_2679.JPG (55.38 KiB) Viewed 2327 times
I can't bolt it all down until my batteries arrive because the frame I'm making for the batteries is going to bolt in under the rear plastic piece, so for now its just sitting together loosely until my next shipment of parts arrives.
User avatar
By toycrusher
Awesome and great job with photos documenting your progress 8-)
User avatar
By dfreas
I've got both motors mounted now:
IMG_2682.JPG (71.9 KiB) Viewed 1952 times
Overall this would be a pretty easy project if it weren't for the fact that I'm trying to keep all the parts within the original plastic body so that it looks stock when I'm done. Because of that constraint I can't add a cross beam over the existing frame without raising the motor too much so I'm forced to bolt into the stock frame. But that ran into all sorts of problems because the plastic frame bolts in right where I needed the motor to bolt on which was also exactly where I needed the new battery frame to bolt up to underneath. The whole thing is ridiculously tight.

It would be much easier if I had a welder, and basically trivial if I were willing to mess up the outer plastic body and abandon the idea of keeping the end result looking stock. For now I'm sticking with it, but I can't really recommend this project to anyone else at this point.

Motor sprockets are about 1/8th of an inch out of alignment with the drive sprockets, and that's as close as I can get them for now. The chain is also half a link too long and the combination of the two means that it throws the chain if I shake the body while the motor is running. I've ordered some half links and I'm hoping that tightening the chain will be enough to make it stop popping off. If not I may have to grind down the motor axle so the D sprocket can slide further down the shaft.

There isn't enough space for a chain tensioner so for now that's not an option.

The batteries arrived so I'm going to switch over to building out the rest of the battery frame and installing the ESC electronics and then come back to the alignment problem last.
User avatar
By dfreas
Stepped away from the motor mounting for a bit to work on things that were more likely to go well. I can happily report that four batteries comfortably fit on a Dune Racer using less than $20 worth of materials and a few hand tools:
IMG_2684.JPG (75.26 KiB) Viewed 1897 times
Aluminum stock makes the frame, PVC conduit spacers and 1/4" bolts holds it securely just under 3.5 inches below the stock frame. Here it is with the plastic body back in place:
IMG_2686.JPG (71.75 KiB) Viewed 1897 times
I had to make a few cuts here and there. I won't bother going into details because if you shift anything slightly one way or the other the cuts would be completely different. I will say that plastic welding is a great skill to learn when messing with these cars. A sharp knife and a soldering iron and you can pretty much reattach cutoff pieces like new. I used that to shorten a portion of the shifter housing that jutted out to far while still keeping all of the wiring enclosed.

I was thinking if you rerouted the car's wiring through the hollow metal frame you could remove the plastic wiring channel and probably fit 6 batteries comfortably on this. But 4 suits my build and I want to keep it as close to original as I can so this worked for me.
User avatar
By Hammer-fm
That's four 12V-18Ah batteries? That's some good juice there :), should be plenty of runtime and power reserve. I haven't gotten a dune racer or anything with a metal frame yet -- having something I could use my welder on would be nice. I actually have a plywood tray attached to the bottom side of the Mustang to carry my 6 9Ah batteries.

The scooter motors should also be a bit more efficient than the stock PW motors. The thing will run all day :lol:
User avatar
By dfreas
Yup, a welder would make a huge difference. With the low to the ground wide body and convenient layout you could basically convert this thing into a full on go kart with a few welds.

Edit: Forgot to answer your question. Yes - 4 18Ah 12v batteries. And I sure hope it does last a long time - four kids and a huge yard means these powerwheels get a ton of use when they are working. My kids basically use them like golf carts to get from one area of the yard to the other.
User avatar
By dfreas
Well I got it all assembled this weekend, and yes - you can fit a chain drive into the stock plastic frame of a Dune Racer:
IMG_2688.JPG (72.52 KiB) Viewed 1867 times
IMG_2690.JPG (68.17 KiB) Viewed 1867 times
IMG_2691.JPG (73.32 KiB) Viewed 1867 times
I was hoping that since only the old gear covers are over the chain drive that I would be able to easily access the chain by removing a single piece. But no, the seat leans back far enough to cover two of the screws on the gear cover so in order to get to them you have to remove the seat, which involves disassembling half the power wheel.

I ran it for about two minutes before the first chain popped off and I discovered just how difficult it was going to be to get to the chain. In order to solve this issue I've ordered a couple of T-handle draw latches to replace the screws. That way any time a chain pops off it will be a simple to get to with no tools.

As for the reason the chained came off to begin with - it turns out that the axle can actually float 1/2 an inch or so either way. In the stock configuration the gear housing pushes outward and prevents this, but the sprocket is much thinner than the original gear box so that is no longer the case. I'll be pulling it apart this week to figure out how to lock the axle in place and prevent the drift that is causing the chain to come off.

Question for anyone else running a chain drive: Does reverse work well in your vehicle? Every time my chain popped off it was because of switching from forward to reverse. The change in direction makes the motor eat the slack in the chain before turning the wheel causing the chain to come off. Tightening the chain and fixing the axle drift may fix this, but if someone out there already knows that reverse just doesn't work well with chain drives it would be good to tell me now before I waste the next two weeks trying to make it work...
By BB_Mike
I have a Razor dirt quad with that style of motor. It has an assembly that bolts to it that serves as the chain tensioner. I search and found a few images of what that looks like: ... G_8358.JPG
from :
There is also a gear reduction on it as well.

You can buy just the tensioner

from here:

I added reverse to my son's dirt quad, so this does come in handy. It serves to wrap the chain more so around the motor sprocket.
Cool looking project you have there. I am curious to know if the matching of motors is important here. I also think that the power from one motor would be more than enough. Then you could just make it a live axle that spins... kind of like a go kart.
Or, keep both motors, and use one for reverse and one for forward, with a relay or DPDT switch. then you can tension the chains accordingly on assembly and not need the tensioner.

Good luck! Be sure to send the video and let us know where you get tires on the cheap! :)
User avatar
By dfreas
That would be perfect if I could do it, but the motor in the pictures you shared looks like it has two bolt holes in the face that allows this to be mounted to it. Mine doesn't have anything like that. This is the first tensioner design I've seen that would actually fit within the space I have though. It's given me something to think about at least - if I can figure out a way to fit a tensioner in this build that would be ideal.
User avatar
By dfreas
I spent about two hours this evening ripping apart the rear axle to figure out what's making the chain pop off and I think I figured it out. There's just too much play in the drive sprocket. The silicone idea filled the gap between the bearing and the wheel gear, but it did it flexibly - which is fine for a gearbox, but apparently terrible for a chain drive because it allowed the sprocket to twist out of line slightly which I think is what was popping the chain so fast.

The solution landed on my workbench when my son finally fried one of the stock motors on his 24v dune racer. I switched the motor out with one of the spares I had pulled off of this project and had the dead motor laying in front of me while I was trying to figure out how to solidly shim the wheel bearing. That's when I noticed that the metal jacket on the stock motor looked like it would be a perfect fit. I pulled it off, sawed it in half and filed off the rough edges and ended up with this:
IMG_2720.JPG (79.43 KiB) Viewed 1780 times
Good motor on the left so you can see the metal jacket I'm talking about. Center is one half of the metal jacket I pulled off the bad motor sitting there empty. To the right you can see that it's a perfect fit if you slide a bearing into each side of it. This whole assembly then slides perfectly into the plastic wheel driver with a 3/4" washer and shaft collar to hold it all in place. Now instead of a thin flexible seal, I have a double wide solid metal seal.

Got it all tightened down and installed and it is a huge improvement in stability of that back axle. I also added a shaft collar on each side of the frame to stop the axle drift problem I was having so the whole thing is rock solid now. At this point my back is killing me from bending over too long so I'll put the chains on and test it tomorrow.
User avatar
By dfreas
I installed the draw latches on the gear cover so now when the chain pops off I can get to it quickly without any tools:
IMG_2721.JPG (70.09 KiB) Viewed 1742 times
IMG_2722.JPG (53.67 KiB) Viewed 1742 times
I put the chain on and we tested it out this morning. I missed the best parts when my son first started and was holding the pedal down. Once it gets up to full speed it really starts drifting like crazy and that scared him so after the first few minutes he went a lot easier on it. It's still pretty fast even with him babying it:
The chain still pops off. Now it will stay on as long as he doesn't make sharp turns, hit serious bumps, or change into reverse but any one of those things will pop a chain. It's because the sprocket it not directly linked to the wheel. The junction between the two loosens up the more the car is driven and eventually it's loose enough to pop a chain. I think I'm going to have to permanently connect the wheel and the gear somehow.

Any suggestions?
By BB_Mike
How about this:

1) The metal sprocket is attached to the axle with a set screw and collar, correct?

2) The electric motor is attached to the body of the vehicle, correct?

3) Then the problem is the floating nature of the axle.

So you need to find a way to "register" or center the axle relative to the body. Perhaps there is some area in that back body location where you can have two collar set screws on the axle, sperated by a piece of body material that the collars pinch up against. This would center the axle. but not be great for wear.

Another option is to drive the wheel axle nuts in tighter so that the axle has nowhere to float to. This has wear issues as well.

another option is to thread the outside end of the axle so that you can have some precision/control to the tightness of the wheels.

Or, go about it the other way... let the axle float, then for the driven sprocket, use a key instead of a set-screw/collar. Grind a slot in the axle for that key. With this approach, you would hope that the chain spinning will keep the driven sprocket aligned and the axle floats around.

I have not tried any of this. Just tossing some ideas out there.
By BB_Mike
Another idea just hit me. The axles in these power wheels do flex. then bend into a U like shape. Moreso with extra batteries and extra large motors and a bigger kid in a high milegage ride on. This flexing of the axle will cause the gear to tilt in and that might be causing the chain to run off.
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