Hey guys, during the offseason my team was discussing ideas for interesting drivebases that would help us stay competitive in the 2023 season, should holonomic be advantageous.
For context, we (team 4788!) live in West Australia and we dont have the resources to buy COTS swerve modules. We have experience with West-Coast-Drives and Mechanum, but both have obvious drawbacks that make them less competitive (in most situations) than swerve.
Ideally, the alternative drivebase would allow us to achieve holonomic motion without impeding on normal tank motion- in the case of an experimental drive system failing, we want to be able to just take it off and have a tank drive. It also means we can maintain the pushing power/defence of tank.
This lead us to a 2-state actuated drivebase we called WASP (West Australia Sideways Propulsion). The basic idea was to place two pneumatically-actuated omni wheels on the back of a west coast drivebase, with omni wheels on the WCD’s front two wheels.
When actuated, none of the (highlighted orange) traction wheels touch the ground.
After further research, we found it was really similar to 1939’s drivebase in 2017
which used the same concept to drive sideways
It seems to be forced to move in arcs instead of straight lines since, unlike H drive, the sideways force isn’t applied to the center of the rotation, creating a moment. However, this could just be what they did in the video.
To achieve straight sideways motion, our solution is to add 4" mechanums to the front wheels of WCD.
To test this, we mounted a perpendicular omni to the back of our 2022 robot, and put mechanums on the front, which worked well, even with full manual controls (tank drive on the thumbsticks, sideways wheel on the triggers).
The video only shows us moving in arcs but we could go straight, it felt identical to driving mechanum. We also tested driving with the omnis ‘undeployed’. The mechanums do not greatly affect how the normal WCD drives.
We’ve also CADded the module on our WCD to check the piston geometry was possible with 60PSI in a reasonable form factor.
In this version we’re using two 32mm bore x 25mm stroke cylinders to lift the robot about 2°. both rear omnis are driven by a single neo through an in-tube gearbox (We’ll also reconsider the use of the vex gears and mechanum wheels😬)
Heres a link to the inventor files if you wish to check it out.
In conclusion, with a proper control scheme and the right game field layout, we may consider this drivebase for 2023.
Cheaper than swerve
Can be used as normal tank in case of module failure
less motors and complexity
Requires switching between traction and agility, can’t be simultaneous and more driver dependant
Basically unproven in competition
Requires pneumatics and consumes some air to deploy
Of course, we haven’t thought of everything. Any feedback is greatly appreciated and we’re happy to answer any questions!