Introduction: Modification of Chinese Ride on Gearbox "Model B" for Use With High Power Brushed or Brushless Motors With a 5mm Shaft.

The following gearbox modification replaces the first molded gear in the gearbox with a manufactured one to allow a much larger pinion to be used. This will accomodate the larger diameter shaft of the more powerful motor and handle the higher torque better by using increased tooth size.

Suitable motors need to be 36mm in diameter with M3 securing screws on a
25mm diameter circle.

Step 1: Parts List, Item 1:

Children's electric car gearbox without motor,Children
ride on remote control car gear box set,kid's vehicle accessories Gear Set "B"

Step 2: Parts List, Item 2:

SS12.5/12B 1.25 mod 12 tooth
Metric Pitch Steel Spur Gear with Boss. 25mm overall length, 15mm tooth width, boss diameter 11.5mm

Step 3: Parts List, Item 3:

PS10/41B 1 mod 41 tooth
Metric Pitch Plastic Spur Gear (30% glass filled nylon6) with Boss. 24.5mm Overall length, 15mm tooth width. Boss size doesn’t really matter as it’ll all be machined away anyway.

Step 4: Parts List, Item 4:

1 Mod 10T High Precision Spur
Gear 45# Steel Pinion Gear With Steps

Step 5: Parts List, Item 5:

10PCS MF84ZZ LF840ZZ Shielded
Flanged 4 x 8 x 3MM Model Flange Ball Bearing

Step 6: Parts List, Item 6:

Metric Hardened & Ground
Steel Dowel Pins 4mmx50mm pk5

Step 7: Parts List, Item 7:

Inner Diameter 4 SF-1 Self
Lubricating Bearing Bronze Sleeve 4x6x4 SF-1 0404

This part could be replaced by any small collar with an outside diameter of 6mm and inside diameter of 4mm

Step 8: Parts List, Item 8:

Slow setting Epoxy glue such as JB Weld or chemical metal.

Something with a cure time of around 8 hours allows it to flow and settle properly.

Step 9: Parts List, Item 9:

Some soft plastic bar stock, 50mm diameter, about 25mm
in length. I used some polypropylene I had kicking about.

Step 10: Make a Supporting Pocket for the Larger Gear.

Take the soft plastic bar stock, ensuring the outside diameter is turned true, and machine a pocket to accept the 41T 1 mod gear with a gentle press fit (about 42.5mm), and bore through to 22-25mm (to accommodate the 12T pinion. Larger diameter of pocket should be about 13mm deep.

Step 11: Bore Out the Large Gear

Using the soft plastic pocket to hold the 41T 1 mod gear
central in the 3 jaw chuck, increase the bore of the gear to match the boss of the 12T 1.25Mod gear, mine was around 11.5mm. Fit should be a gentle push fit (by hand).

Note, the moulded bore may not be perfectly central so use a centre drill before increasing the bore with a longer drill bit to allow a boring bar to be used.

Step 12: Fitting the 12T Steel Gear to the Large Gear.

Continuing with the 41T gear in the soft plastic pocket, remove the boss and counter bore the gear to a depth of 4mm, and to a diameter to accommodate a firm press fit of the 12T 1.25 mod gear into the counter bore.

Step 13: Securing the 12T Steel Gear Into the Large Gear.

Fill the counter bore shoulder with epoxy glue (fill the shoulder from edge to edge so it would look triangular in cross section) and press the 12T 1.25 Mod gear into the counterbore. The epoxy should fill the gaps between the teeth of the 12T gear. Even though the counterbore should be 4mm deep I was left with 11.5mm of steel gear protruding after pressing... (I say pressing, I hammered it in with a nylon faced mallet)

Step 14: Finishing the Gear

Once the epoxy has set (allow a good 24hrs) put the assembly
back into the soft plastic pocket, but with the steel pinion facing into the 22mm pocket hole.

Increase the bore of the steel gear to 8mm, and then from the face of the steel boss cut a counter bore 2mm deeper than the steel face out towards the teeth. Exact diameter isn’t important as long as it clears the shaft support collar in the gear box side.

Step 15: Fitting of the Flange Bearings

Fit ball bearings into each side of the new gear assembly and test fit the 4mm shaft through the bearings, I found mine was too tight and had to skim the 4mm shaft down by about 0.1mm to get it through.

Step 16: Fit 6mm to 4mm Bushes

Push the 4x6x4 bronze bearings into the gearbox halves.

Also, If the gearbox moulding is a bit rough, the hole where the motor pinion comes through may need to be cleaned up / opened out to 13mm to allow clearance on the 10T 1Mod pinion.

Cut the length of the 4mm shaft down to the same length as the original 6mm shaft it will be replacing (I think mine ended up 43mm long). I used a bench grinder to grind it down to length as it’s really hard steel.

Step 17: Test Fit New Gear

Assemble the gearbox halfs with only the new 4mm shaft and new gear installed. By putting your fingers through the big hole where the main output gear is normally located, check for free movement of the new gear and that there is a small amount of movement of the gear along the 4mm shaft.

If the gear is tight or there is no play increase the depth of the counterbore on the back of the gear a little.

Step 18: Assemble Gearbox With New Motor.

Reassemble all gears and new motor into the gearbox and check for meshing (the gear meshing should be pretty spot on)

To ensure a tight fit of the motor into the gearbox moulding, I wrapped the end with insulation tape until its diameter was 38mm. This provided a snug fit and held the motor securely.

Apply additional grease to the gears, I used a lithium based grease with PTFE in it to reduce friction.

Step 19: Test

Test the gearboxes with the ESCs they will be using to ensure smooth operation of the gearboxes.

Install them back in the ride on car and enjoy!