2 Speed Gearboxes FPS?

[Dr.Gusta]

What were your guys gear ratios, wheel diameters and FPS in low and high gear? I know it will very year to year based on the game but I am looking for a kind of baseline.

[Mike Marandola]

We used:
VEXpro 2 CIM ball shifters
60:24 3rd stage
4 inch HiGrip wheels

It gives us about 4 fps low and 8.4 high. That is a lot slower than I would've liked and it had a negative impact on our game. We want to get the 54:30 3rd stage to give us about 5.5 low/12.6 high but they have been out of stock for a while. We did try out the 50:34 3rd stage but we didn't have enough power and were unable to turn in high gear.

[RonnieS]

Originally Posted by Mike Marandola

We used:
VEXpro 2 CIM ball shifters
60:24 3rd stage
4 inch HiGrip wheels

It gives us about 4 fps low and 8.4 high. That is a lot slower than I would've liked and it had a negative impact on our game. We want to get the 54:30 3rd stage to give us about 5.5 low/12.6 high but they have been out of stock for a while. We did try out the 50:34 3rd stage but we didn't have enough power and were unable to turn in high gear.

You don't find 5.5 FPS too slow for an open field? I was playing D in our low gear which was 7-8 FPS and still was able to play it well. I know if i saw a robot that slow trying to play D, I would just use high to completely evaid them, you would never be able to get close. I can see it more useful in a broken up field like 2010 but not like 2014.

[Mike Marandola]

Originally Posted by Ronnie314

You don't find 5.5 FPS too slow for an open field? I was playing D in our low gear which was 7-8 FPS and still was able to play it well. I know if i saw a robot that slow trying to play D, I would just use high to completely evaid them, you would never be able to get close. I can see it more useful in a broken up field like 2010 but not like 2014.

Of course 5.5 is too slow. High gear would be the default and low gear would just be for pushing.

[RonnieS]

Originally Posted by Mike Marandola

Of course 5.5 is too slow. High gear would be the default and low gear would just be for pushing.

I'm still confused on why you need to be that low to push? I guess if you want to push 3 robots in a row but at that point I would see it as more of a waste of time from an offensive point of view...and I would never encourage a team to go straight defense anyways so I would want to cater my drive more towards my offensive production rather than its primary defensive capabilities. Of course I would want it to be able to play D but that is a thought after I fulfill my offense requests.

[Mike Marandola]

Originally Posted by Ronnie314

I'm still confused on why you need to be that low to push? I guess if you want to push 3 robots in a row but at that point I would see it as more of a waste of time from an offensive point of view...and I would never encourage a team to go straight defense anyways so I would want to cater my drive more towards my offensive production rather than its primary defensive capabilities. Of course I would want it to be able to play D but that is a thought after I fulfill my offense requests.

There are only 5 ratio options and one spread option for the 2CIM ball shifters and as I said 5.5 low and 12.6 high is the fastest we can go with 4 CIMs. I would like to go faster in low gear but we currently can't. Hopefully next season we can upgrade to the 3CIM ball shifters so we can have far more ratio and spread options.

Originally Posted by Mike Marandola

There are only 5 ratio options and one spread option for the 2CIM ball shifters and as I said 5.5 low and 12.6 high is the fastest we can go with 4 CIMs. I would like to go faster in low gear but we currently can't. Hopefully next season we can upgrade to the 3CIM ball shifters so we can have far more ratio and spread options.

It won't kill you to increase wheel diameter to get a faster speed.

[JamesCH95]

We ran around 7fps in low and 14.5fps (accounting for some drivetrain speed losses) in high last year with 2-cim ball shifters on 6in colson wheels. That setup worked great for us.

I like to have 2spd transmissions be barely traction-limited in low gear and let the high gear fall in the 12+ft/s range.

[Oblarg]

Originally Posted by Ronnie314

I'm still confused on why you need to be that low to push? I guess if you want to push 3 robots in a row but at that point I would see it as more of a waste of time from an offensive point of view...and I would never encourage a team to go straight defense anyways so I would want to cater my drive more towards my offensive production rather than its primary defensive capabilities. Of course I would want it to be able to play D but that is a thought after I fulfill my offense requests.

If you want to push continuously with a 150lb robot with a high wheel COF (say somewhere around 1.3-1.5) without any danger of tripping the breaker, 5.5 is very reasonable. I saw a lot of ~5/15 splits for 6CIM drives at worlds. It is always nice to give yourself a bit of headroom. It's not so much of a sacrifice to lose a bit of speed on your pushing gear when you have a shifter and won't be moving any serious distances in that gear, anyway.

Of course, with a lighter robot or one with less grippy wheels or one that doesn't draw much power other than the drive, one can (and should) gear more aggressively.

For reference, our preseason drive (which, we hope, will also be our competition drive this year) is going to be geared for around 6/16 with roughtop wheels.

[Mike Marandola]

Originally Posted by Andrew Lawrence

It won't kill you to increase wheel diameter to get a faster speed.

We are running a AM14U so thats not an option. The only way for us to change speeds on our current robot is to change the 3rd stage.

Originally Posted by Mike Marandola

We are running a AM14U so thats not an option. The only way for us to change speeds on our current robot is to change the 3rd stage.

I'm pretty sure you can swap the 4" kit wheels for the 6" ones.

[AdamHeard]

Please show me good, real data for a COF of 1.3-1.5....

Originally Posted by Oblarg

If you want to push continuously with a 150lb robot with a high wheel COF (say somewhere around 1.3-1.5) without any danger of tripping the breaker, 5.5 is very reasonable. I saw a lot of ~5/15 splits for 6CIM drives at worlds. It is always nice to give yourself a bit of headroom. It's not so much of a sacrifice to lose a bit of speed on your pushing gear when you have a shifter and won't be moving any serious distances in that gear, anyway.

Of course, with a lighter robot or one with less grippy wheels or one that doesn't draw much power other than the drive, one can (and should) gear more aggressively.

For reference, our preseason drive (which, we hope, will also be our competition drive this year) is going to be geared for around 6/16 with roughtop wheels.

[Oblarg]

Originally Posted by AdamHeard

Please show me good, real data for a COF of 1.3-1.5....

I don't have any on-hand, but I am pretty sure I've heard claims from multiple people that wedgetop is in that range.

Maybe one of these days I'll purchase a quantity of all the available tread materials and test it myself.

[Mike Marandola]

Originally Posted by Andrew Lawrence

I'm pretty sure you can swap the 4" kit wheels for the 6" ones.

Unfortunately only in the long and square configurations. We are using the wide configuration. I should have specified.

Originally Posted by Oblarg

I don't have any on-hand, but I am pretty sure I've heard claims from multiple people that wedgetop is in that range.

Maybe one of these days I'll purchase a quantity of all the available tread materials and test it myself.

1640 did some CoF tests. No wedgetop though.

[RonnieS]

Originally Posted by Mike Marandola

There are only 5 ratio options and one spread option for the 2CIM ball shifters and as I said 5.5 low and 12.6 high is the fastest we can go with 4 CIMs. I would like to go faster in low gear but we currently can't. Hopefully next season we can upgrade to the 3CIM ball shifters so we can have far more ratio and spread options.

I would also look at other chassis options...although the new AM chassis might and probably will have changes, I would hate for you to back yourself into only that option.
IMO, you can find better options than last years AM chassis, maybe my opinion will change when the new one is released. Just my 2 cents.