Chief Delphi - Automatic catcher?

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Re: Automatic catcher?

We have an automatic catch function using the same matixbot ultrasound rangefinder (may be a different model, but certainly the same brand and packaging). One of our students got it running on an ardunio - the threshold "catch" distance is set with a potentiometer, and the cRIO is sent a boolean digital signal (basically, "Catch" or "Don't Catch").

LEDs hooked into the arduino let us see where the catch threshold is, so we can make tweaks by powering on, messing with the potentiometer and waving a ball around in the pit. No Arduino code changes, no cRIO code changes.

The issue we've found with the autocatch is the timing very much depends on the speed of the ball - a lobbed ball from the human player needs to trigger the catch late (short range) so it doesn't snap shut before the ball is contained, but a shot with a lot of velocity (over the truss) needs to trigger earlier so the catch is in motion when the ball gets deeper into our robot. We're messing around trying to find a sweet spot, but we might have to tune for one and operate the other manually. We could add a second digital out for a second threshold, as well - have a "catch" and a "human load" threshold distance.

Our robot release video has some demos of this - I think many (most?) of these were automatic catches.

Re: Automatic catcher?

Quote:

Originally Posted by EricS-Team180 (Post 1349407)

We are currently using one LV-EZ4, looking up at a shallow angle, from the base of our catapult. It "works", but the threshold of where we want to trigger our grabber and hands is varying too much. ...say from an analog threshold of ~9 to ~30. The result is that we sometimes miss the auto-catch, and the operator has to recover manually. That doesn't sound like a big deal, but time is precious. For now, we've decided that the ultrasonic - mounted as we chose - is not as reliable as we want it to be. Unless we calibrate before each match, or understand the drift, we'll likely swap it out with an optical sensor at our first regional in Orlando.

@JamesCH95: have you seen your threshold move around like that?

@JoeRoss: you bet we used that voucher :)
Thanks,
Eric

In a word: no. We have them aimed near-vertical and they trigger very reliably as the ball drops into our catcher. It sounds like you have a geometry issue as much as anything else... from what you describe it seems like you're trying to bounce sound off of the ball nearly tangent to its surface.

Re: Automatic catcher?

Quote:

Originally Posted by JamesCH95 (Post 1349430)

We have them aimed near-vertical and they trigger very reliably as the ball drops into our catcher. It sounds like you have a geometry issue as much as anything else... from what you describe it seems like you're trying to bounce sound off of the ball nearly tangent to its surface.

...hmmmmm Good point. Depending on the ball's entrance, the geometry could be working out to be close to tangential. That's something to take a closer look at.

Thanks
Eric