Steerable Wheel Assembly Parts for XRP robot

Update: 7/11/2024

Created brackets for XRP and tweaked some tolerances.  I tried to design them so they did not interfere with the ultrasonic or reflectivity sensors.  I printed and assembled this much on a real XRP robot.  Each side requires (2) M3 25mm screws and nuts and a few drop of superglue.  (4) M3 25mm screws and nuts needed and perhaps O-Rings for the rims.

I set the wheels lower than the rollerballs so you don't need to remove the roller-balls to try out the wheels.  There is only one screw that connects the wheel assembly to the bracket on each side so the wheels are easy to take off and you can leave the brackets attached the robot (the brackets could be useful for other things too).

I printed at 0.28 layer height.  No support need except for the linkages (touching buildplate)

Still need to design linkage to connect the left and right wheel assemblies together so they move in tandem (118mm center to center for the linkages) and also include a servo mount and servo linkage before it can be tested.

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This is a servo driven steering wheel assembly intended as a building block for the XRP robot to experiment/convert to servo driven steerable wheel(s).  

The rectangular bracket must be fixed to the robot

A servo motor is used to connect to the linkage (optional M3 screw holes provided for connecting a linkage to the servo).  Custom linkage(s) and a servo mounting method needed for your custom application(s).  When I have a robot, I will look into mounting further.

An M3 screw long enough to go all the way through the bracket (bracket is 22 mm long) with an M3 nut is needed.  The side of the screw holds the rotating hub in place and the same screw also acts as a swivel between the fixed bracket and linkage piece that the hub spins in.

optionally a drop of superglue on the hubcap to lock the wheel on and a drop of glue to keep the m3 nut from backing off the screw since it will be loose to allow the swiveling.

Note, I like assembling the XRP wheel 180 degrees flipped on the assembly (as in real pic) versus the wheel being flipped in the model screenshots.  Either way is possible.

Print at 0.2 mm layer height and 100% infill and support on (for the linkage part)

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For reference, I included the default XRP wheel these parts should work with from the unofficial XRP model by Jacob.  The XRP wheel stl is not not my design.  I included it for convenience.  It was leveraged from here:

https://cad.onshape.com/documents/c913e8123c02ee33921a5971/w/7d14522ced56234cd785a73a/e/9d00469367efc1f33d913be0

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I also included a wheel/tire that I printed out of Hatchbox 032 C TPU at 240C and .28 layer height which I found fits the wheel very tightly.  Note that this wheel is a larger diameter (58mm outer diameter instead of 55mm) than the stock o-ring because the TPU I used is less flexible than the stock o-ring.   I also included a wide version (with the same 58mm oversized diameter) that has a flat outer surface to see if it will have more traction but I have not tried the wide version yet.  I find that the TPU has to be warmed up to fit over the rim but once it is on there it is tight and not slipping on the rim.