It’s been a while since my last post on the design of my robot car. The reason is that I have been moving to a new house and also have been quite stuck with the wheel design for my robot car, and it took many iterations to get the design right. This post is thus all about robot wheels and the design of creating an awesome drive system for the robot 🙂
The first iteration I started out with a more traditional wheel design with a simple rubber wheel. This wheel has a suspension system with a spring based actuation based on a simple triangular geometry.
There are quite some obvious challenges with this design, one being that if you have 4 motors/friction components meaning you can not really drive this setup without some form of active steering. My Design did not include this type and this was also not the intention, the wheel setup was to validate the suspension design. Altho the suspension was weak it was ok enough for such simple wheels and therefore I kept the basic design for the moment.
The design goal was to create some Mecanum wheels that would allow omni directional drive system. I had looked into buying these wheels online, but seeing prices of 130-150 dollar for a set of 4 wheels I thought why not print them myself. Initially I looked through existing designs and settled with something that I found on a blog / thingiverse (http://pleasantsoftware.com/developer/3d/2010/04/23/its-printable/) and modified this to fit my Dynamixel Servo’s.
Altho it worked more or less, the main challenge here was that I never got the rollers to roll freely enough. This together with lack of friction made the drive quality quite poor and not reliable when driven in a ‘strafing’ mode for example as is visible in this movie:
Mecanum Wheel v2
Based on this I decided to take a fully different approach and start design my full wheel myself. I created a properly angled roller setup and used bearings for all the rollers. It took me many iterations and improvement cycles to get this right, there was always some challenge in terms of getting perfect frictionless setup. It took me as many as 20 prototypes before I settled on a final design.
Next to this the rollers where printed in a TPU based filament so they are more rubber like as you would have in real mecanum based wheels. This has significantly improved the wheel roller quality and resulted in the following single wheel setup:
After having finished the mecanum wheels I found out the current suspension simply was to light for the more heavy wheels and there was to much flex in the system. Inspired by this Makeblock robot (http://openlab.makeblock.com/topic/567e4f409964feea3d37bbdb) I started a design and ended up with the following:
Driving the Rover
The result of this is quite good, the robot has a perfect strafe and axis rotation.
Hope this shows that it is possible to create a fully open source robot design with mecanum wheels that work quite well. If there is interest I can upload the 3D files to github in the coming period.