Vex Pro Ball Shifter Questions
 

I've been working on an off-season gearbox project, and I have a few questions about the vex pro ball shifter.

For my project, I'm designing a 2 speed, 3 CIM gearbox, with power takeoff. I've designed a few in the past, but they're all too heavy, so I decided to try with parts from a vex pro ball shifter. The three CIMs are set up to drive two separate ball shifter shafts. The first operates like it would in the normal gearbox, shifting the drive motors from high to low, and the second is only driven by one input gear, so the output from the shaft will only be connected when that input gear is selected.

I have three questions

1. Can I use the ball shifter shaft with 3 CIMs without it breaking?

2. We bought some ball shifters in the past, and I'm pretty sure that you can (by hand) move the shifting rod in between the two gears and get to a "neutral" gear, where no output happens. Is this correct, and would it be possible to spring load the shifting mechanism so that when there is no air the system, it returns to "neutral"?

3. Has anybody done something like this before with positive or negative results?

Re: Vex Pro Ball Shifter Questions
 

1. Yes.

2. Yes, and no. If you want to have a neutral, you'll have to buy a 3-position pneumatic cylinder with strokes of 0.25in and 0.5in.

3. We're doing something similar right now. I'll keep you posted when we're done.

Re: Vex Pro Ball Shifter Questions
 

2. The neutral position is in-between high and low (full in and full out)

Re: Vex Pro Ball Shifter Questions
 

What T^2 said above, for the neutral you can't easily get it with springs.

But FabCo and Bimba sell a 3 POS cylinder. The hole pattern matches with the current mounting and the cylinders are basically interchangeable with the SMC cylinder used on the ball lock. So you can easily get the neutral position.

-RC

Re: Vex Pro Ball Shifter Questions
 

If you can get a servo to act as the cylinder, you could accurately position the shifter stuff.
You may like checking this out: http://www.andymark.com/product-p/am-2297.htm

Something similar may be what you want!

Re: Vex Pro Ball Shifter Questions
 

No team has accomplished this on the ballshifter as of yet; see 67's attempts last season. If you're going into this project blind, don't do this.

Re: Vex Pro Ball Shifter Questions
 

I'll also note that with dog shifters, those folks that use servos tend to switch to pneumatics as soon as practical. The legal FRC servos tend not to have enough power to shift on the fly, or so I hear (and I've heard it from enough sources to figure there's some truth to it). No comment on the linear servo, though; I don't think anybody's tried it in a competition yet.

Re: Vex Pro Ball Shifter Questions
 

I have yet to try the linear servo shifter. It appears that something like that would solve the issues I was having with the other servos setups, trying to get the rotatary motion lined up with the "slop" in the shift rod.

Re: Vex Pro Ball Shifter Questions
 

With a linear servo setup, the problem is that you need to be at a complete stop to shift, which rids you of the point in having a shifter. You would typically use the shifters to accelerate quickly, and then accelerate slowly, to a higher max speed!

Re: Vex Pro Ball Shifter Questions
 

That's actually the problem with ANY servo setup, or so I hear. I think 330 tried servos on a shifter back when I was a student, but never on a competition robot; we used pneumatics on EVERY shifter we had (drill motor trannies and AM Gen2s).

Re: Vex Pro Ball Shifter Questions
 

The only team that I know that had used shifter to accelerate more quickly is 33. Everybody else generally uses shifter so that they have a higher top speed and a good pushing gear.

Re: Vex Pro Ball Shifter Questions
 

Yeah, I guess, but if used properly, shifters can be used to accelerate to a moderate speed faster, and then increase the top speed! Geared down with speed reduction, you will get tons of torque, what you need to accelerate faster. Geared down high, you can increase the top speed by a lot!

Re: Vex Pro Ball Shifter Questions
 

A careful analysis of the factors at work in drivetrain will show that with typical FRC top speeds, this is not the case. Even in cases where battery voltage drop limits acceleration, the acceleration difference between a low gear 8fps and high gear 18fps, for the first 8fps is minimal. You would be talking about less than .3 - .1 seconds here, over a distance of 50 feet. Of course, gearing for absurdly high speeds, say 30fps, would yield a greater acceleration difference. However, at these speeds, you wouldn't even be able to accelerate to top speed in 50 ft, not to mention the currents you would be drawing.

When you consider the time and air it takes to shift each time, any small benefit gained would be a drop in the pond when driving in a match.

Re: Vex Pro Ball Shifter Questions
 

This doesn't even start to mention the complexity of correctly writing auto shifting code. For the small benefit is it really worth all that time?

Re: Vex Pro Ball Shifter Questions
 

When I drove 3476's auto-shifting Vex pro ball shifter robot, it was rather seamless, and it seemed worth it.