Motor driven catapult gear ratio

For those with motor driven catapults, what are your setups?

2 BAG motors at 466:1.

Edit: That’s pulling the catapult down – we are not using the motors to throw the ball. It’s unclear what you’re after here.

I think he’s referring to Boom Done type shooters…like Spectrum’s and our robot.

To OP, 15.33:1 for our shooter

Yes we are looking to change our catapult firing mechanism from springs to motor driven.


Our springs were inconsistent and wore down after like 50 shots. Also we couldn’t move the catapult arm without releasing it completely. Motors would be more consistent and reliable.

What factors do you think might make the motor performance change during the course of a match.

Also we couldn’t move the catapult arm without releasing it completely.

What does the above sentence mean?

He means that the catapult arm can only be stopped halfway through its motion path with a great deal of effort in a fairly unsafe manner. We had the same problem in 2008 with a spring driven catapult. Also, dry firing was extremely risky, for us.

We have a 2 cim toughbox mini (i dont remember the ratio) with a belt driven 3:1 if i remember correctly from there. We have power and speed to spare.

We use a motor driven catapult with a toughbox+2CIMs+35 chain and sprockets.

Total reduction with gearbox and chains is about 25:1.

We also use a pneumatic cylinder on the back with ~8" lever arm that applies 40 lbs of pressure or so.

It can score with just the motors but the range is limited to a small window around 8’ out, withe the pneumatics it is significantly stronger.

we have been having trouble with consistency with our motor shooter specifically when the battery gets low

6 cims, 12.75:1 gear reduction (3 cim toughboxes) and a 2:1 chain reduction totaling 25.5. We can pour the ball off the front, shoot from 18ft, full court or anywhere between.

Here is our reveal video wich showcases our close end adjustability:

What is your catapult arm made of?

Our arm is basically 1/8 x 2" aluminum riveted to 3/4" angle aluminum for support. It is a flattened “J” curve in shape. The center of the ball is ~17" from the fulcrum.

Do you have any pictures of your entire setup?

The arms are made of thin walled 1 inch square aluminum tubing. After 80 shots there is no sign of any wear and tear on the arms. We used thick wall on our practice bot and noticed a substantial reduction in performance.

There are JVN style pegs to the back made of schedule 40 fiberglass tubing (PVC would work just as well). We are stilll determining the optimal lenth.

We are using 2 CIMs + 2 775s. The two 775s are in a dual input adapter Versaplanetary with a 4:1 ratio. That gearbox and the 2 CIMs are plugged into a VEXpro single speed gearbox at 5.33:1. After that there is a 12:26 and 15:26 stage.

Arm length, arm travel time, release angle, cradle construction, cradle geometry and a lot of other variables go into making a motor catapult work well. We’re still tuning ours.

For consistent shots, the arm geometry and also the motor speeds play a huge rule. We have both a pot and an encoder on our arm to do both position and velocity feedback.

Ours are 15:1 Modulox transmissions driven by CIM motors. Lots of power, shoots quite far consistently, looks pretty cool too on our non professionally made 3/4" marine grade plywood shooting frame. :ahh:

we use a ~50:1 overall ratio for 2 full size Cim’s on a 2 ft arm, but we are still tweaking the numbers.

1x Bag Motor
1x VersaPlanetary 25:1, 1x VersaPlanetary 10:1 totaling 250:1 reduction.
1x Choo-choo
468lbs worth of springs.
It works. The orbital gears like to shatter sometimes but I’m 98.979% sure we fixed that.