Introduction: Knex 12v Motor Upgrade

About: Just into K'nex

In this tutorial we are going to replace the standard motor in the Knex 12v Worm Geared Motor.

There are many ways to improve the performance of these things, ranging from gearing up or down to increase torque or speed, or just adding more motors to your construction. However, end of the day, the most effective way to change your motor is to literally change it.

Note: You need a soldering iron!

Step 1: Knowing Your Motor

In my project I didn't want to find ways of rigging different mounts to knex, or paying hundreds of pounds on hubs etc, which eventually lead me to cracking open that motor and learning everything I could about it so I would know exactly what I needed. Sadly it didn't survive my toolbox of hammers approach.

But I did learn exactly what type of motor it was.

RS380SH 12v

Finding the datasheet on the other hand wasn't so simple. I'm pretty sure its this one based on the stall current:

The important part however is the type: RS380, which is: 27.7 diameter, 2.3mm shaft. The length however varies, and we'll get to that in a few steps.

Step 2: Finding the Replacement

RS Components has a good selection of motors, however only one of them was suitable for me. I needed both more speed and torque, which partly meant searching for a 24v motor. The one I used was the Mellor 24v.

The partial data in the screenshot was the only information I could find about this specific motor, just by googling.

Step 3: Making Sure Its Right

Here I did make a bit of a gamble, because the specs didn't indicate which type of shaft it was, and I couldn't easily tell from the picture. But just like the original motor, it must have a spline shaft in order to grip the worm drive.

Step 4: Getting Started

Pull off that worm drive. Its on there pretty tight, but don't worry, there aren't any rivets holding it in. Just give it a big pull.

Step 5: Salvaging Parts

Take the back ring off with a hex driver or pair of pliers, and pull (don't twist) the lid off. You can then remove the motor.

Take a pair of cutters (the big ones) and snip off the power port where the conductor meets the motor connectors

Step 6: Solder Them On

Now here you might do a better job that I did, but you need to solder on the power port onto the new motor. Ensuring that the position is the same as the original. All RS380 motors include a red dot to indicate the "live" side.

Step 7: Mount Adjustments

Like mine was, your motor might be slightly longer than the standard one, so get a hack saw and saw off about half of the inner lid. There is a mold line indicating where the lid grips the case, so you shouldn't need to cut off more than that, assuming you need to at all.

Step 8: Done

Put everything back together and you're finished. Make sure to push the worm drive back in hard.

Step 9: Last Thing

A note about Knex parts. They aren't very strong. My use case is to place two of these custom motors across each other so they drive the same wheel. The stall torque is so strong, that the clips holding the worm wheel in place actually fly off the rod if I force the device to stop.

Also it ruined one of my worm wheels, but luckily those can be bought separately.

And finally; most similar sized motors are still 12v, but a more powerful motor of similar voltage will use far more current than the standard adapter will provide. Because my robot is going to be battery powered I opted for 24v so it wouldn't drain the battery too quickly.