Passive Expansion Mechanism

For tower takeover, our team has run into issues with the 18" restriction at the beginning the match. We would like to be able to passively expand the chassis at the beginning of the round past 18 inches. But we don’t have any extra motors and we need all 8 motors which rules out pneumatics. We are currently using a basic X-Drive. I know that this is fairly vague mostly because I don’t have our robot on hand and didn’t take any pictures, but any advice on a general mechanism that could do this would be greatly appreciated.

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Do you mean physically changing the position of the wheels? Or just tip bars?

You can usually use the movement of the robot or another already existing nearby subsystem to “power” the passive mechanism. If you rubber band a system just right to fall down after x amount of force is pushed on it and then use a passive lock to keep it there you can use the drive of the robot to expand. You can also use, for example, a lift the lift up and after a certain height the mechanism falls out of a catch that previously held it back.

I understand this too is pretty vague, and I would have showed you how we let down the intake for our cap bot last season if we still had it together.

edit: crap I’m stupid, I literally skipped over the most important part of the post


Here are a couple videos you might find useful:


For SS, I used tip bars. I used one of the trapezoid shaped channels (I forget what they’re called) and the green sliders. The channels would have rubber bands attached to the side close to the center of the robot and the other end of the rubber bands were attached to the edge of the base. Then, I had I think an axle that would go through the base into the channel. The axel was attached my lift with string, so that when it lifted up, the axle pulled out and the tip bar slid out. Hope this helps.

If you want, you can add wheels to the ends that spin freely so that it won’t tip at all

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Fred V did something like what you are describing:


God he did make some really nice robots back in the day. Was an honor to see his bots in action.


You could try linear sliders thought they are somewhat flimsy. You would just run each side of the drive train in opposite directions to expand or detract.


You could use a passive lock that uses rubber bands and a fixed standoff.

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