Does anyone have (or know where to find) the Sherbrooke (Ri3D) cad?

Hello @yolomcjabber,
We’re in the process of uploading the CAD, i’ll post it here when it’s done.
Happy to see your interest in our work :slight_smile:

Wow, that is very similar to the design we are working towards. Let me see if I get the lift arms right. Pneumatics lift the lower arm section. The chain and sprocket on the lower arm cause the upper arm to move in unison. As the arms extend it pulls up the straps reaching their limit where the grabber flips into position. Then a winch pulls it down.

Sure works well. We were planning on a drive motor to extend the arms up and pull them back down. The long arms result in a rather large torque requirement and a lot of gear reduction. That’s doable but high torque and long arms has me a bit nervous. Maybe the winch is more reliable.

Hi Eric,
You got that right! The only correction I would make is that we let the strap loose because we are using a ratchet to make sure the robot doesn’t come down at the end of the match. That way, the winch can only rotate in one direction. If we had a mechanism to disconnect the ratchet, the arms could unroll the strap, but we didn’t have time for that.

As for your concept using the drive motors, I think it could work, but as you said you are going to end up with huge torque requirements and pretty high mechanical stresses in the joints. Also, because of the gear reduction, you should consider the time it takes to actuate the mechanism.

We went with a winch because those are simple to use and can be easily adapted to the required torque and speed. Also, the pneumatic cylinders make sure the hanger quickly gets up there.

Good luck with your design and don’t hesitate if you have any other questions!

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Here is the link to our web page. It includes the links to the two main parts of our robot:

I was looking for the design of how you made the spools for your winch mechanism, but it isn’t in your CAD. (unless I’m blind, which I might well could be.) Would you mind sharing how you made your spools? My team is using a similar type of flat rope to your straps to climb.

@Ofournier might be able to tell you a bit more about it, but I believe the strap just rolls around a shaft with hubs preventing the strap from moving side-to-side.

Thanks! I’ll go ask him.

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