3D Printed worm drive gearboxes

With the aim to slow the robot down a bit and combat the issue that the robot would not stop straight away when the joystick was released, I started looking at alternative gearbox options. The one option I knew that would resolve both of these issues and give a very compact gearbox solution was to use a worm drive. These enable high reduction ratios and are very difficult to back drive, meaning that when the motor stops turning, the wheel will stop very quickly and won’t run on.
I had a look around online and knew that it was possible to 3D print a worm drive gearbox but I wasn’t sure how practical or long lasting these would be. I decided to give it a shot and set about designing and printing a prototype. Part 8 of the RC Robot video series shows the design, build and testing of the gearbox.

 

 

The gears were generated using this OpenSCAD generator: https://github.com/chrisspen/gears I modified the gears to include hubs for attaching them to a shaft. I also designed and printed a custom housing for the gearbox complete with bearings to support the drive shaft and one end of the worm gear. The worm gear was tricky to print well and I ended up printing it in one piece, stood on its end. I had to print this very slowly and still the print was not perfect but was good enough. I had a few failures of the worm gear early on and had to go through a few design iterations to add strength where it was needed to get a functional part. I also had to adjust the gear spacing a couple of times, once by modifying the gearbox housing and second time by altering the size of the spur gear. I found that if the gears were meshed too tight it would put too much force on the worm gear and cause damage, if meshed too loose, the backlash in the gearbox would be excessive. The video shows the assembly and testing of the gearbox and it works really well. Its a bit noisy but some lubrication helped a lot. I am hoping that as the gearbox is used, the gears will wear in slightly and the gearbox will operate more smoothly and quietly. How well the gears wear over the long term will need to be gauged as the gearbox is used.

I went on to build a second gearbox that needed to be a mirror of the first so that I had a gearbox for each side of the robot. At this stage I decided that I would strip the RC Robot down and build a new chassis to mount the worm drive gearboxes to and make a few more improvements along the way. Part 9 of the video series shows the rebuilt robot and details the design changes.

 

 

I’m really pleased with this version of the RC Robot platform. I drives nice and steadily with plenty of torque. The original spur gear gearboxes provided a gear reduction of around 3:1. The worm drive gearboxes give a reduction of 7:1 in a very compact unit. This slows the wheels down considerably and gives a good amount of torque to the wheels. I have tested the robot quite a bit now and it is easy to control and stops immediately when the joystick is released.

I now have a nice sturdy platform to work with and I will be continuing this project by adding more functionality to the robot. My aim has always been to automate this robot, even though I am calling it the RC Robot (I may need to rename it at some point in the future). The first step will be the addition of some more sensors so come back soon to check on the progress.

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