# Using 100:1 NEO for a catapult help

Conversation came up in the shop, how would it work using a motor to be the primary source to power a catapult?

I’m thinking of the rev bore pass through encoder, but I have no clue how or what implementation should look like?

Thanks!

These are 3 very different thoughts (gear ratio, motor use with a catapult mechanism, and feedback sensor choice), so I’m not quite sure what you’re asking.

Can you clarify (via pictures, CAD, or even just a sketch on paper) what your design looks like, and then outline what your concerns are?

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Are you considering using the Neo to charge whatever serves as the spring of the catapult or as the primary launch mechanism?

We used a 2 mini-CIM electric catapult in 2016 and it worked very well. The gear ratio between the motors and the arm was about 22:1. The encoder was the US Digital optical encoder that fits a Toughbox Mini. We considered it this year as well, but the different ball trajectory and its reduced angular travel of the catapult made it a challenge. We abandoned the idea for this year.

Was thinking of using it primary , not to pull down

100:1 won’t give you much velocity on the ball with the arm length that fits in a FRC robot.

NEO has a free speedof ~5600 RPM. With 100:1 reduction (assuming an unreasonable 100% efficiency in the gearbox), you’d get 56 RPM for the output shaft, or just under 1rev/sec. Again, this is max theoretical speed with no load. Now, add in load from the mass if the ball/your catapult arm/etc., and factor in efficiency losses from the gearbox, and you’re likely somewhere in the realm of (wild guess) 20 RPM, or 120°/sec. With an 18" arm, you have a total travel distance of ~36" (crude math: PI*(2*18)/3) in the span of 1 second, or roughly 3 feet per second.

If you throw that into a projectile motion formula and solve for x (horizontal distance), you’ll see what @electroken is referring to.

Of course, you can always change the gear ratio in the calculations above until you get a more favorable result.

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We are using NEO motors for electric catapults this year. Our current iteration is a 25:1 Maxplanetary gearbox and a ~22" measurement from axle to ball center. Note in the pictures below that we had to place the arm pivots relatively high to get enough angular travel. This produces enough power to launch from against the hub at less than 50% motor power, so there is excess performance to allow further adjustment of gear ratios, arm length, etc.

The control setup is very simple for now: simply set up the soft travel limit in the Spark Max controller and request a desired power level to launch.

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Who’s that good lookin guy in the knight helmet?

We used a cam

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