Motor driven catapult gear ratio

[EricWilliams]

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.

[matthewdenny]

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.

[themick07]

Originally Posted by matthewdenny

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.

What is your catapult arm made of?

[matthewdenny]

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.

[themick07]

Originally Posted by matthewdenny

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?

[pilum40]

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.

[kk052]

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.

[Exla357]

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.

[thmeans06]

8:1 Toughbox with 2 Cims. Then another stage reduction on the chain that drives the arm. Mini Toughbox didn't have enough torque to get the ball to full speed in the travel time of the arm.

[roystur44]

Our Choo Choo winch consists of:

2 RS-775 18V motors connected with the VexPro dual input mount.
One VexPro Versaplantary transmission at 300:1 3 stages (10:1,10:1, 3:1)
winding a set 18:84 VexPro gears.
1400:1 total gear reduction
Pulling down 2 7" trampoline springs to 14" takes less than 8 seconds
provides over 240 lb stall load (unloaded output)

[Max Boord]

Originally Posted by themick07

What is your catapult arm made of?

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.

[AllenGregoryIV]

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.