Say there’s a hook on the back of a robot that is used to drag the mobile goals. When the robot is moving forward or backward, the hook is holding the mobile goal. But when the robot is parked (not in motion) the hook is up. However the hook is neither motorized nor pneumaticly powered. Instead the hook falls and rises due to the acceleration and momentum of the robot.
You certainly could do it if you’re willing to work at it. I expect it will be difficult to build and even more so to fine tune with the parts available. First I would clarify some things. For example, if it’s turning on the spot, (neither forward nor backward, nor not in motion), what’s happening?
The way I immediately though of is using a physical pendulum. Make sure there is a bit of friction, you want the motion to be critically damped. (Ask if that doesn’t mean anything.) You also want to have catches at each end. Then you run a cord from it off to the side and then wherever. If you accelerate suddenly from rest (forward or back), the pendulum swings and catches. But the acceleration as it reaches constant velocity isn’t enough to free it. So the cord has been pulled and remains pulled to activate one way. If you stop suddenly, it is enough for the pendulum to become loosed from the catch, falling to the middle and letting the string go, which allows the hook mechanism to pull cord back and go to its other position.
If you want to measure motion (not just acceleration) physically, not electronically (since you don’t want to send signals to a motors/pneumatics), you’ll want something physical somehow connected to the wheels to gauge whether they’re rotating or not. Otherwise you’d probably drag something on the floor to get exactly the same thing. Since you want forward or backward to turn into the same thing, you’ll need to convert the motion. I could see putting a slider on a bar. Intake thingies push the slider away from the middle, in opposite directions based on direction. Use springs or elastic to try to bring it back to the middle, failing so long as there is motion. You could now run a cord like with the pendulum.
Those are my two quickest off the top of my head. I’d love to see a successful implementation of any of these or another method.
Well, that’s even harder then. The pendulum method won’t work with spinning. The other method might, but probably not. Of course, there could be a second cord to a mass toward an outer edge that would use a centrifugal pull on the cord to pull off the same thing.
Honestly, I expect a transmission that switches motors from driving to moving the hook might be a lot easier.
We did some tests with dragging the mobile goal and the results vary drastically based on whether or not the foam tiles are dirty or clean. On clean tiles, dragging the goal seemed pretty viable but on a somewhat dirty tile(like the ones at most tournaments) it was actually pretty hard to drag so you might wanna consider that. Anyway i agree with @Callen , a transmission would be easier
(Put on your imagination cap)
Imagine a ratchet wheel with the pointy bits facing clockwise. Now imagine a ring that goes around the outside of the wheel with springy pointy bits facing inwards in such a way that the ring is driven when the wheel is spun one way, but not spun when it spins the other. Unless your imagination is really good, move to a pen and paper now. Take this mechanism, and make one copy of it, and add two gears such that one gear is attached to each wheel and make them mesh. Attach one sprocket to each ring, and add a chain. Make a copy of this whole mechanism, and mirror it along the plane where the wheels and rings are positioned. Attach one of the gears from one of the mechanisms to your drive train, the gear you pick does not matter. Repeat the last process to the other mechanism and drive train side. Attach a long shaft to one sprocket from each side, and feed those shafts into the sides of a differential. Mesh the casing gear of the differential to a gear train that increases the spinning speed. Finally feed the output of the high-speed gear train into a governor (what’s a governor? ) and the output of the governor will move the hook up and down.