2 Speed Gearboxes FPS?

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.

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.

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.

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.

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.

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.

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.

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.

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

1640 did some CoF tests. No wedgetop though.

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.

Someone needs to have a lesson on significant figures! :smiley:

Cool testing, though I’m not sure I buy into the omni wheels having a CoF of 0.36 on carpet. That’s on the order of brass-steel or plastic-steel.

1640’s tests do not appear to account for where the center of mass is. That is a fundamental problem with getting raw values from that methodology for CoF (particularly when using an actual FRC bot as opposed to a block of steel, for example). If CoM is biased forward for Step 3, it will cause a higher CoF raw calculation, whereas a high CoM (z-axis, height of robot) will cause a lower CoF raw calculation.

However, it is good for a rank order when comparing wheel types, so long as the wheels are the same size or the chassis frame is always the same height from the floor.

As for 1885’s single speed in 2014, a post-mortem analysis using video, Ether’s Simulation and the original AndyMark orders confirm we were only 10 ft/s after losses, single-speed. There was a mixup somewhere and the end result was us driving about 2ft/s slower than originally planned. In hindsight, 12ft/s single speed was the correct target to get around most defense, and this year we’ll have better QA for incoming orders ;).