Behind the Bumpers - FRC 2881 Lady Can - Double Catapult! Double catapults with vision, flamingo climber with 3d printed hook to prevent swing and a intake that flexes in to prevent damage 2881 Lady Cans have built a fantastic Rapid React robot. Get the full overview from the team on Behind the Bumpers.



For this style catapult is it only powered by the motor or is there any form of assist (elastic, springs, pneumatics). How does the programing side work. I would expect you could do a velocity PID controller to get the arm up to speed (desired speed would be determined using camera). Then you would stop it when it has passed a certain setpoint (also determined using the camera) which would be the release angle.

Also what is the process for determining the gear ratio for something like this. I would guess you could do some graphing to figure out what the max velocity you would need to throw the ball and design the gearbox to run at that speed at around 75% power.

Edit: Found this explanation Double catapult - #20 by LadyCans-FRC2881

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Here’s some more info from our programmers about how we control the catapults.

We use voltage control mode on the SparkMAX and drive the motors at 11 V for all shots, no matter the range. This helps to keep our shots consistent across a match as the battery voltage droops. Then, based on the hub tracking from the camera, we set a soft limit to control how far the catapult runs. Naturally for shorter shots (such as when our bumpers are against the fender), the catapult does not gain as much speed as it does for longer shots.

The mapping of camera targeting to soft limit is done by tuning several shots across the range of the catapult and using linear interpolation between those tuned shots. Since there is a delay between the two catapults, the same soft limit is used for both catapults; there were a few times (before we added this!) where a cargo in the camera frame would get mis-interpreted as the hub (causing us great confusion since the two shots would be wildly different!).

The final software control is the delay between shots. When closer to the hub, the shots tend to be more of a lob, with more up and down movement than across the floor movement. Therefore, a longer delay is required between the two catapults to avoid the cargo from hitting in the air (the high-point being the most problematic time). Longer shots, on the other hand, tend to be a lot flatter, and can therefore be spaced closer without hitting in the air.

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