Gearbox Question
 

We are having trouble winching down our catapult. We currently have a toughbox mini with 2 mini cims in it. We have the ability to put 2 cims in it but we are currently pretty far from the power we want to have for our catapult (like halfway or less to our goal and the motors stall out). We also have a reduction after the toughbox mini with a 19 tooth gear driving a 48 tooth gear. I wanted to know of any gearboxes that really gear the motor down and offer a lot more force. Also if the difference in power between cims and mini cims is significant enough could this solve our problem? If you could post a link to the website for the gearbox it would be greatly appreciated.

Re: Gearbox Question
 

The mini Cim has about 2/3 the torque of the full size CIM

Spool size is also part of the equation...what are you using to wind up whatever it is you're pulling?

Re: Gearbox Question
 

Also make sure that your winch release isn't slowing you down-- we found out at our week 0 this weekend that the winch we were using (a COTS boat winch) was introducing so much friction when we released that it cut our shot length to 25% of our new version.

Re: Gearbox Question
 

We made our own spool and it has a 2" diameter. Right now it is really holding our shot back but we plan on decreasing the rolling friction it has. Do you think that by decreasing the spool diameter that will significantly help?

Re: Gearbox Question
 

Decreasing the diameter will increase the force applied to what the winch is pulling. But it will also increase the time it takes to move it.

Re: Gearbox Question
 

Team 4055 had a problem with tensioning our catapult. I don't know exactly what is a problem with yours but we had a few issues.

1) We had one CIM tensioning the catapult

2) There was a large amount of friction because we didn't use bearings (Bad decision)

3) We were applying force to our arm at an extremely small angle.

Fix

1) We designed a completely bolt on mechanism. It was a 4.5 to 1 ratio with two CIMs.

2) We upgraded to a 1/2 in keyed shaft with Oil Impregnated Bronze Bearing :rolleyes:
http://www.amazon.com/Spyraflo-PB1-5...bronze+bearing

3)Force has it's maximum efficiency when the force is applying perpendicular to the arm. Relocating our attachment point for our winding strap helped.

Re: Gearbox Question
 

On our winch, we used an RS 775 with a 1:100 versa planetary gearbox (1/2 inch Hex output). We estimate that it takes about 50-75 lbs to pull the catapult back and it does so in roughly 3 seconds.

P.S. Our spool has a 2 in OD

Re: Gearbox Question
 

Our winch works great! Here's what we did.

We use a VexPro 2 speed ball shifter, with the balls removed from high gear to convert it to neutral. We power it with two CIMs. (We first tried mini-CIMs, but swapped out one of the three CIMs on each drive gearbox with the miniCIMs.)

We use a VexPro 1/2" hex shaft for winding the 1" wide military-grade webbing that pulls down the catapult arm. The shaft fits right into the end of the gearbox.

The most significant thing we did for reliable winding is that the webbing is anchored to the shaft at a point about 2" away from the final winding point, so that it winds helically along the length of the hex shaft instead of in a single roll. This dramatically reduces the final diameter of the wound-up strap, resulting in a much lower effective gear ratio at the end of the stroke when the tension is the highest.