pic: 3CIM Ball Shifter

[Andrew Schreiber]

Originally Posted by evanperryg

The problem with having such an insanely high gear is that the robot will be very hard to control. Another issue with such a huge difference in gearing is momentum. This year, my team used AM supershifters at 5/12fps. If we we were in high gear then switched to low at full speed, we would tip over 75-80% of the time. Imagine how bad it would be going between 17 and 5.

I'm pretty sure 111 did a 3-speed this year. Also, how could 4 speeds possibly be beneficial, even as an autoshift?

Back then we had a lot less power, to get reasonable acceleration and still have a high top speed was hard.

[Lil' Lavery]

Originally Posted by evanperryg

I'm pretty sure 111 did a 3-speed this year. Also, how could 4 speeds possibly be beneficial, even as an autoshift?

Their initial design goal was 3(+) speeds, but the method they chose allowed for 4 speeds just as easy as 3. Essentially, each shifting mechanism they incorporated doubled the potential ratios. One mechanism would be two speeds, two mechanisms allows for four potential speeds. If they added a third, it would be 8 speeds. Rather than try to explain it in greater detail myself, I'll simply use the wonderful resource they posted on the gearbox (with nice pictures that explain it better than any amount of paragraphs ever could).
http://www.chiefdelphi.com/media/papers/1580

[AlecMataloni]

Originally Posted by evanperryg

I'm pretty sure 111 did a 3-speed this year.

We used the COTS two-speed ball shifters from Vex this year. Nothing too fancy.

[apalrd]

We didn't want a 4 speed, we wanted a 3 speed. We wanted a fast and very fast gear, like our current design goals for high and low, but we had less power, so we needed a low low for pushing (remember this is back before bumpers) and couldn't get away with the fast-low we like now.

But, with the resources we had, it was easier to build a 4 speed than a 3 speed (since we end up with 2 2-speeds in series). The shift patterns are then low/low,low/high,high/low,high/high, with a different ratio spread of each of the 2-speeds in series. But the 2-3 shift (going from low/high to high/low) requires a double-swap shift which is just plain nasty to execute synchronously between two shifters while under power. A possible solution is to run it like a 3-speed with two options for 2nd gear, and essentially jump-shift past the 2-3 shift. This would add complexity to the shift scheduler, although more than 2 speeds already adds complexity to our shift scheduler.

A ball shifter design can do any number of speeds just by adding more gear pairs to the shafts, so it's possible to do a 3-speed instead of a 4-speed, but it's much harder to manufacture than the dual 2-speed with andymark parts or dual 2-speed mesh shifter design (or even the dual 2-speed ball shifter).

So 4 speeds was easier to build, but the 2-3 shift is bad.

[Lil' Lavery]

Originally Posted by apalrd

A ball shifter design can do any number of speeds just by adding more gear pairs to the shafts, so it's possible to do a 3-speed instead of a 4-speed, but it's much harder to manufacture than the dual 2-speed with andymark parts or dual 2-speed mesh shifter design (or even the dual 2-speed ball shifter).

For reference, 222 has been running a 3-speed ball shifter since 2004.

http://www.chiefdelphi.com/media/papers/1539

[Andrew Schreiber]

Originally Posted by Lil' Lavery

For reference, 222 has been running a 3-speed ball shifter since 2004.

http://www.chiefdelphi.com/media/papers/1539

I thought they'd gone to just running 2 speeds as of late?

[camtunkpa]

Originally Posted by Andrew Schreiber

I thought they'd gone to just running 2 speeds as of late?

This is correct. We only ran 3 speeds in 2004. We didn't find the added complexity and weight to be worth the added gear ratio.

2013 was the first season since 2004 that we haven't made our own transmissions. This season we went with the vexpro ball shifter and will likely use them again in the future FWIW.