Motor driven catapult gear ratio

[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.

[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.

[TheKeeg]

Originally Posted by themick07

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.

I am just curious how you plan on achieving this considering the robot is bagged all but 6 hours. I am sure there is a plan in place, but it seems like a pretty large design change for competition season. Have you already designed/built the new catapult and just need to place it on the robot it or is it an addition to the original shooter?

[SRaymond]

2 CIMs to a toughbox mini to a chain drive (not sure of the sprocket's tooth numbers)

Works like a champ!

[IndySam]

4 775's on 5:1 Versas with a secondary reduction on 2:1 for a grand total of 10:1.

Its a linear shooter not a traditional catapult

[marccenter]

For us, we are using dual mini-toughboxes with 1-CIM and mini-CIM, one on each side, then double chain reduction of 15 from the CIM output to a 26 tooth sprocket, then a 36 tooth sprocket to a 96 tooth sprocket. Total reduction should be nearly 27:1. We are using 1/2 EMT loop connected to two arms. The 96 tooth sprockets were made by our sponsor (Andy Mark six hole pattern - 1.875 inch bolt circle).

We're throwing the ball from white line past the other white line, over the truss, during the Southfield MI event. We missed some shots because we didn't have the shooter dialed in perfectly (made 2, missed maybe 5, 10 pointers) and hit the upper target area bouncing over the top.

We also calibrated for shooting into the 1 point goal over robots. We were 1 for 2 with little practice.

Thanks CD for previous posts that led us in the direction to have more velocity and less torque (F = 1/2 * mass * velocity squared)

Our design is based on the Boom Done design completed in the Robot for 3 Days competition. This year's motto: If Joe's team can do it in 3 days, we can do it in 6 weeks!" (4-6 high school students, 1-1/4 engineers, 1 dad for 6-8 hours).

Best regards,

[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)

[rkbot]

our team uses 2 rs 775's in a dual input adapter which goes into a 4:1 vex versaplanetary which runs into a 153:1 2000lbs ATV winch gearbox with anot outside reduction with our sprockets which i believe is 1.8:1 or so. It rounds out to about 1150:1. for out shooting mechanism we are using 2 snowmobile suspension springs out of a early 1980's Polaris.