Today we're going to upgrade the motors and pinions on the new Grave Digger ride on toy from Walmart. Common complaint on these cool little rides is that they are too slow. The stock motors are only 14,000 RPM @ 24v, so replacing them with the Traxxas 5675 motors will provide a big speed boost. Expect the speed to increase from the stock 5mph to between 8-9mph after this upgrade.
This is a relatively simple job. You're just going to be removing the rear wheels and axle, pulling off the gearboxes, putting the new motors in, then reassembling the rear axle/gearboxes/wheels. You'll also need to upgrade the fuse to 40a and the self-resetting breaker to 40a, as these motors draw a lot more power at startup. If your kids are bigger (>50lbs) or your riding area is grassy/hilly, you might experience issues with blowing fuses. We solved this issue by installing an ESC kit.
Between this and the soft spring upgrade, our Grave Digger has become a lot more fun for the kids.
Step 1: Gather Tools and Parts
40a Cartridge Fuse - (might want to get a spare or two, but your local auto parts store should have them)
Various Crimp Connectors - (a kit like this is nice, if you don't already have a bunch laying around)
2mm Hex key
Philips screwdriver or drill
Step 2: Remove Rear Wheels, Axle and Gearboxes
Lift the rear of vehicle with jack stands or a milk crate or whatever you have laying around that can support 100lbs or so.
Unscrew the 1/2" nut off each wheel. Pull the wheels off, then tap the axle out of it's raceway.
Disconnect the wires from under the seat that lead to each motor. They're simple click-fittings.
The gearboxes are held onto the frame with two philips screws. Remove those and pull the gearboxes off the vehicle.
While you have the boxes off, now is a good time to run a round file around the hole in the body where the green conduit carries the wire to under the seat. The stock holes fit very tight around the conduit, but having a little play in there will help them slide if you choose to upgrade the springs later on.
Step 3: Disassemble Gearbox Covers and Remove Motors
There are six philips screws that hold the the two sides of the gearbox cover together. Remove those and the gearbox will come right out of the cover. It might help to remove the three screws holding the green conduit piece on as well.
There are two philips screws that hold the motor into the gearbox. Remove those and the motor comes right out.
Step 4: Modify Motor Wiring and Attach New Pinions
The new motors come with male bullet connectors. You'll need to cut the harnesses off the stock motors, then crimp a female bullet connector onto the cut end. Connect these to the new motors. The new motors have dual plugs for r/c application, so cap the second wire with shrink wrap or another bullet connect that isn't connected to anything.
Check your new pinions vs the stock pinions to ensure they are exactly the same pitch and tooth count. (You can likely use a 14t or 15t pinion to increase top speed further, but I've yet to test that). The pinions just slide onto the shaft of the new motor and are tightened with a set screw. I like to use blue loctite threadlocker to prevent them from coming loose during driving.
Now install the new motor into the gearbox with the two screws used to hold the stock motors on. Spin the wheel adapter on the gearbox to make sure the motor turns freely and there is no grinding. If it won't turn, you might need to adjust the depth of the pinion on the shaft to make sure it lines up with the gear inside the box.
Then reassemble the rear axle, gearboxes and wheels, which is just the reverse of step 1.
Step 5: Modify the Battery Fuse and Circuit Breaker
IMPORTANT: This modification will require that you periodically check the vehicles wiring and motors' temperature during use to ensure safety. Grassy, hilly yards with heavy children will cause more strain on the electrical system than hard, flat surfaces with lighter children. Warm weather will also further overheating issues. Your application is unique and you need to monitor this for your childrens' safety. After this modification, I only allow 1 child at a time to ride the vehicle to keep the stress on the electrical system to a minimum. If the motors or wires are too hot to touch, they are being over-stressed and you need to stop usage, allow them to cool and then change your riding conditions (less weight + flatter surfaces = easier on motors).
These motors draw a lot more current at startup than the stock motors. They will instantly blow the 30a fuse. Unscrew the factory fuse holder, cut the wires and splice in a 40a cartridge fuse. Do not exceed 40a and do not eliminate the fuse entirely. The fuse is for your child's safety.
You will also need to replace the auto-resetting circuit breaker. It is located on the underside of the vehicle. There is a plastic strip that covers the wiring channel. Remove the strip and find the breaker (small black rectangle in the picture). Wire in the 40a circuit breaker. Make sure to note the line (wire from battery) and load (wires to motors/accessories) and attach them to the correct side of the breaker. Replace the plastic cover on the wire channel.
Step 6: Upgrade Other Systems (Optional)
Batteries: Consider upgrading your batteries while you're performing this mod. The stock 7.2Ah batteries have a pathetic run time with stock motors... and these beastly Traxxas motors exacerbate that. The stock battery will only have a 10~ minute run time with the new motors.
I've installed dual 20Ah batteries to increase the ride time to 30~ minutes. 22Ah batteries would be better, but I had one 20Ah laying around already, so I only had to buy one more.
Shocks: The stock springs on the shock absorbers are too stiff to function properly. I've upgraded to softer springs that really put some bounce into the ride. You can get a set from MLToys.
ESC: Adding an Electronic Speed Controller to any power wheels is a great way to add advanced features like variable throttle, separate brake pedal, parental remote kill switch, soft start and the ability to safely increase voltage without destroying your gearboxes. For ESC kits done right, check out www.EastCoastPowerUp.com . Their customer service is top notch. We've added the East Coast 1000w DIY kit to our 24vGD and I highly recommend it.
Step 7: Go Play!
You're all done! Now go have fun with this monster of a ride on!
Runner Up in the
Wheels Contest 2017
DerrickS47 made it!