Reducing Friction in Shooter
 

My team used a winch based shooter using sergical tubing. A VEX 2 speed gearbox would pull back the tubing then pneumaticly shifts into a neutral gear (neutral gear was created by removing the "balls" form the high speed stage. The issue we are having is it takes about 14lbs to un spool the rope while in the neutral gear this greatly reduces our acceleration on the shooter. Oh and just to let you know we bagged our electronics and drive base but held back our manipulator mechanism.

Re: Reducing Friction in Shooter
 

All things considered, if you only need 14 pounds to release your mechanism you're in good shape. The 3/4" bore piston at 60 PSI pushes with 26.5 lbs of force. It pulls with somewhat less force since the piston rod takes away some surface area.

Are you having trouble shifting the piston under load? Does it take too long? An easy fix would be moving the gear to the end of the shifter so that you push to shift to neutral. If you still need more force, it is possible to get creative and mount a bigger piston to the mechanism, but be warned that the Vex shifter components (bearing and e-clips) cannot handle a ton more than 30 pounds of force.

One last thing: are you sure it's the gearbox that's slowing you down?

Re: Reducing Friction in Shooter
 

Chris, I think what he means is that once into Neutral, the resistance in the launcher system consumes 14lbs of his available shooting force, thus reducing the energy remaining to put into the ball.

OP, is this correct?

If so, can you describe your system in a little more detail? What material are your "moving part" surfaces made of, etc.?

Re: Reducing Friction in Shooter
 

I think you miss understand. It shifts normally but the issue is the force it takes to actually pull the rope off of the spool when it is in neutral gear is 14lbs so their is 14lbs of resistance when the sergical tubing retracts. Yes the friction is in the gear
Box we are 100% sure.

Re: Reducing Friction in Shooter
 

I understood this to mean that more of the energy stored in the surgical tubing is being used to unspool the rope and spin the drum than they're happy with.

If possible, a simple solution might be to counteract the force require to unspool the rope and spin the drum with a spring acting on the other side of your pivot. It'll take that much more energy to load the catapult, but if you were to counteract the torque of the spool and rope with a spring, you'll get a bit more energy into the ball.

Re: Reducing Friction in Shooter
 

Sounds like something got assembled incorrectly and/or something is damaged. I would suggest taking the gearbox apart and checking everything very carefully. Clean off grease etc. to get a good look at everything and see what's wearing or binding.

I would also make 110% sure that you're actually getting into neutral and disengaging completely.

Things to check:
1) All bearings rolling smoothly
2) Abnormal wear on gears (a little black discoloration is okay)
3) Any wear on the sides of gears (very bad)
4) Wave-washers installed in the proper locations
5) Gearbox housing distortion
6) Any side-loading on the output shaft
7) Any slight misalignment in how the gearbox is mouted

Pics would go a long way, especially of disassembled components.

Re: Reducing Friction in Shooter
 

Ah, sorry about that misinterpretation. I'm a bit brain dead after exams. How much reduction do you have after your shifter, and how big is your winch? Putting reductions between the shifter and the output is a trade off between ease of shifting and friction after release.

Can we get a picture of your setup? It sounds like there is something funky going on friction wise. We have an 80lbf CF spring shooter running off a winch one reduction down from the shifter without (very) significant friction.

Re: Reducing Friction in Shooter
 

Wow thank you guys for all the replies I can't post pictures because well I am at school :) I will take a video of me taking apart the gearbox tonight so you guys can get a full understanding of what I am asking.

Re: Reducing Friction in Shooter
 

Did you measure this, or is it the result of a calculation based on the observed shooting distance (or lack thereof)?

What is the radius of the winch roller?

Are there any gear ratios (including sprockets and/or pulleys) between your gearbox output and the winch roller?

Re: Reducing Friction in Shooter
 

i'm going to take a shot in the dark and say the problem is you have 3 bearing on the shaft or have bent the output shaft.

Also try measuring the 14lbs number with no air in the system side load on this type of bearings is not fun

Re: Reducing Friction in Shooter
 

We just wrap the rope around the peice of 1/2" hex shaft. We use the high torque third stage offered by VEX for their ball shifter and I measured it with a fish scale attached to the rope and unspooling the rope by pulling on the scale. It read out 14lbs consistently.

Re: Reducing Friction in Shooter
 

Here's what I think you are saying. Correct me if it's wrong:

There's a substantial speed reduction gear stage that's still connected to the winch when you release it.

You are pulling with 14lbs at a radius of 1/4"

How is the 1/2" hex shaft supported?

Re: Reducing Friction in Shooter
 

Hearing this, the one immediate suggestion might be to try to use as large of a "drum" as you can to wind up your rope. Obviously, this would impact your ratios but unspooling a tiny drum is harder than unspooling a larger LIGHTWEIGHT drum.

Re: Reducing Friction in Shooter
 

With all misconceceptions that everyone is working through, I have a vauge idea what we are trying to accomplish.

So you have a couple of options:
1) Go with a larger diameter spool. 1/4" is really small, 2" probably will do the trick. You want to minimize the amount of revolutions you do on the spool.

2) Tie some surgical tubing to "Spring Load" your spool. The idea is that as you wind the winch back, you pull on the surgical tubing more. Spring force is translated to the unraveling of the spool without using the force to catapult the ball.

3) Make sure you follow the 45 pound withholding allowance rules.

Re: Reducing Friction in Shooter
 

Isn't this the same as having more spring power on the shooting mechanism itself?

Maybe I'm misunderstanding this suggestion...

This is a reasonable solution if the drawback motor/gearbox has additional pulling capacity over what they are currently using but I assumed not.