Team 2451 pwnage p-drive offseason prototype chassis

Pwnage P-Drive Prototype Chassis CAD

Simple single stage gear reduction, WCD chassis rail design for use with MINI-CIM, CIM, NEO and Falcon motor types. Designed to aid autonomous driving precision.

Download the CAD files at our GrabCad link below:


Is that an encoder mounted up there?

Is this a shifter?

I got this error when trying to load the model:

GrabCAD is not able to view this model

Failure reason: Unknown


Yes, there is an encoder on top of the frame rail…

I’ve added a step file for those that aren’t on the newest version of Solidworks. Let me know if you still have issues downloading.

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Why mount the encoder above (and with a non 1:1 pulley), rather than driving it off an axle?


Load the GrabCAD step. It has a nugget of genius.

Kevin, this looks very similar to something we are doing in the offseason. I was hoping you would be willing to answer a question for me.

We have never done chain-in-tube before and we have been doing some experiments to get our center-to-center distances dialed in. We tried adding 0.012", 0.015", and 0.018" to our C-C distance and it was not enough. I pulled open a sketch in your CAD and saw that your C-C was 14.035". Is it a safe assumption to say 14" is the ‘perfect’ distance and the 0.035" was the length added to compensate for the stretch?

If the answer is yes I would like my team to test a 0.035" set up and see the results. This looks great, I really like the setup!

Hmmm… interesting follower wheel adaptation. I guess in a drive configuration that already has corner omnis, maximizing tractive force is not the primary concern anyway, so sacrificing ~11% (assuming even weight distribution onto each axle and that the follower is 50% of the width of the drive wheel) of your normal force is not a dealbreaker. Curious as to what benefit they perceive by monitoring both the active shaft AND the follower wheel (monitoring for loss of traction?).

We have seen different “add-on” amounts needed for 221 System sprockets and for Vex sprockets. It will depend on the design of the sprocket and the machining tolerances .035" is a little much as we saw a little cogging with new chains, but this amount has worn in nice and worked for our setup perfectly.

This setup also has interchangeable outer bearing blocks that allowed for experimenting with wheel drop on the same chassis. So chain length will vary slightly as the wheels are moved up or down for different drop amounts.

Be careful with chain in tube, as the centrally located rivet holes will interfere with the chains! You need to offset the rivet holes to match your chain locations to avoid the rivet bulbs interfering with the chains. We spot drilled the offset holes needed to integrate these new frame rails into an existing practice robot.

We ran 12.393 with the Andymark 17T sprockets (.018 C-C Adder) and found that it worked quite nicely.

Funny you say this, we have actually designed this in already. We are not using Versa-Tube for our chassis but we are using plain 2"x1" and offsetting our rivet holes. I appreciate the rest of your input as well!

We are using the AM-3999 (17t) sprockets and old chain. We have a few running theories about what could have caused us to be off, or we didn’t add enough on our C-C. It makes me feel better that someone else used a similar value to us. I should add that we are using old, worn in chain on this test.

Note that an odd number tooth sprocket pair (17-17) will require a spacing that is a multiple of 1/4" + 1/8". So 8.00" would not work as a base spacing, it would have to be 8.125" base, plus your tensioning adder. That may or may not have been your problem.


Here’s a good thread on chain in tube:

That frame rail is the old frame rail.
I pulled the wrong one out of the model by accident.

The one we are using on the robot currently is 13.893" between bearings which is .018" added to center to center over theoretical distance.

I have updated the CAD model on GrabCad to include the correct frame rail.

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