Catapult - ratchet/potentiometer

Somewhat related to other thread … but different.

We have a Catapult supported by a ratchet (axle) and potentio-meter. We use potentiometer to get the catapult to certain position to load balls. At this instance the ratchet takes it over and holds the catapult. Once balls are loaded, I use another button to push catapult further when it encounters the chipped teeth and fires off.

The problem is that when I add more rubberbands (tension), the axle (ratchet) chipped away the sprocket teeth edges.

Question : If the sprocket breaks in the competition, looking for options without rachet.
With the above method, we can bring the catapult to desired position to load balls, by holding a button - say btn7L. Once balls are loaded, how do I use another button to push it a little bit further so that it fires off (chipped teeth) ? because if I release btn7L, the rubber bands will pull it upwards. How do I transfer the power to another button while still holding the position.

I tried simultaneously holding another button (btn7L and btn8R) that was supposed to give power to motor, but it didn’t work as it should, and the potentiometer held the position.

Thoughts ?

Did @meng or @Riptide or @Got a Screw Loose or others use something like this ?

Thanks in advance.

Hey! A reference! Yay!

I put my ratchet on my slip gear. I don’t have any clear pictures, but the ratchet was always engaged. My potentiometer would be on the axle with the arm, and the ratchet would be coupled with the slip gear. The slip gear only moves one way, allowing for the ratchet to do its job at all times.

I had a statement where I would hold a button (let’s say 6U) until the potentiometer read over a certain value. That button would then go null and wouldn’t activate anything. My 6D button would then just start the motor for however long it took to fire. (Very quickly)

I used a pre-fab Vex ratchet. Pm me if you want specific pics, but I don’t have any very clear ones. Explaining them here would create clutter.

I take it back. Another button giving power to catapult while potentiometer is holding works.


But is that really the best use of your finger in that moment? Sure, you totally could. But wouldn’t it be easier to design something to do it for you?

you could make a good ratchet in less than 20 minutes.

If you post pictures of the ratchet we could have a look and try to figure out the problem. Plenty of teams have very durable ratchets that survive for long periods of time without getting damaged.

Think your main concern should be getting a ratchet that will withstand your holding torque.

So it is a case of either the ratchet is too flimsy or the holding torque is just too excessive.

It could also be that the axle I interpreted you using isn’t the best tool to use. Maybe you could post a couple of pictures to help us better envision your specific system?

Maybe you could use a long scew with spacers resting in the sprocket groove? I don’t know the configuration of your custom ratchet.

Thanks for the insights … this will be useful. The team definitely wants go with a ratchet … but wanted to know the back up if the sprocket breaks during the game. If the sprocket breaks … it will take the kids (middle school) some time before they can put it back :slight_smile: … and can miss a part of it.

But - good to know (that even without a ratchet) that the potentiometer on it’s own can hold it , and then another button fires off from that point

Hold on, the potentiometer is a sensor, and exerts little to no holding force. It would be in the code that the motor would be running for as long as the potentiometer tells it to. And even then, the motor would be using a lot of power to do so, hypothetically.

understood … we have the code associated with potentiometer …holding the catapult in place.
Fyi - our ratchet system -