I built an XRP mecanum chassis. I used the same layout for the battery and circuit board as well as the drive motors. I will post the CAD files on GrabCAD and post the link here. There is room for 2 battery packs for extended life. The outer bumper retains the clip-on interface for accessories. The range finder and line follower clip right on and the stock wires are long enough to reach the board. I tried to keep it as “stock” as possible.
These are the wheels I used, they are close to the same diameter as the stock XRP wheels and have the same shaft connection as the motor so they push right on.
For programming I swapped over to the WPILIb so it can be programmed in Java. This will be a learning tool for our FTC team, so Java is more applicable. So far it works awesome in the teleop mode. Haven’t done too much autonomous with it yet.
Next step is to add a PWM board via the QWIIC so I can add more servos for a manipulator of some sort. Having a hard time finding Java libraries for using the I2C port, but that is a topic for another place.
@toml21
Welcome to the XRP forum. Thanks for sharing your mod of the chassis.
While many here will infer the rationale for your new design, this description of Mecanum wheels may help others to understand your motivation:
I look forward to seeing further development of your variant!
Good call. It is an educational system so important not to leave out the educational piece. The mecanum design allows movement in any direction. When working thru the kinematics of the system I learned that it could be programmed to pivot around any point in space (had never really thought about that before) so it has been fun mapping different center points to buttons on the controllers. I currently have it set up so by default it pivots around the center of the robot, but I have the center points of the marker holders mapped to a couple buttons. The operator can choose to pivot around either the front or rear marker with the press of a button. Kind of fun.
It measures 245mm x 250mm. It can certainly be printed in one shot. I was having a hard time getting it to print in mine because of some exclusion zones on the print bed.
The snap together with a little epoxy has been holding up fine. I’d rather do it in one print tho.
This is awesome! Thank you for sharing the project and CAD files, and good job finding mecanum wheels that are compatible with the motors! We had the idea early on the in the design process of the XRP about mecanum wheel support, but ultimately didn’t get around to it. Really glad to see that you’ve done it, this is super cool!
It was mostly luck of the draw on the wheels working, but that is a pretty common shaft, so the props is to you all for specifying that. I’m sure there will be all kinds of cool stuff coming out of this. I just fried the board hooking it up to 9.6V so waiting on a replacement for that.
@toml21, your design inspired me to design a 1 piece frame in Tinkercad. With the work that @neilrosenberg did by adding the components into it, it made it pretty simple to put together. Here is a screenshot of the design. I’m hoping that the motor mounts will be strong enough on the front.
I also put together a frame to try Omni wheels as well in an X drive pattern. I’m not sure how well this will work, but here is a screenshot of that design.
Very nice! Your motor mounts should be plenty strong I would think. One suggestion is to add a second battery compartment. Running the 4 drive motors eats the batteries up in a hurry.
I like the Omni wheel layout too. I imagine that should work just fine!
so waiting on a replacement for that.
Glad to see the Tinkercad bits and pieces were useful.