Gearing for 12 (fps)

I know there are other threads on this, I’ve seen them, and none have answered my question.

I suggested to my mentor that we gear for about 12 to 13 fps for max speed. He told me that was a ridiculously fast speed, and that last year our top speed was like 6 fps, something I don’t think is right.

So my question is this: IS 12 or 13 fps a really fast speed to gear for, like my mentor said, or is it a perfect speed to gear for, like I said?

Thanks, and I appreciate the help.

no. twelve is a pretty typical speed for multipurpose single gearing. 6 is a good speed for a lower gear with a switching gearbox, because it allows a robot to push opponents around more effectively, but is not a very fast speed for maneuvering on the field, especially considering that the field is fairly open this year. On the other hand, having a slower robot might give better fine control and make it easier to balance, but that could be achieved without a permanent slow gear.

In 2010 and 2011, we had CIMs on 9:1 reduction gear boxes and 6" wheels, and it served us well*. I’ll let you do the math on just how fast that is, and come to your own conclusions.

*in both cases we wish we had the ability to downshift for pushing power, but not all the time!

Thanks!

Last year 973 geared for 7 and 17 Ft/s with 2 cims in drive. Personally i think 12 is a little slow but with the field separated this year gearing might be slower among teams.

We’re using a single speed gearbox (CIMple box, to be exact), along with 4 inch wheels, so a speed like that will be hard to achieve, since it’s our first time using 4 inch wheels and pseudo-creating part of our drive train.

Thanks for the input, though! We want to try a 2 speed transmission either next year or the year after, so we’ll take your speeds into consideration!

I would suggest a bit more conservative than 12 if you have intentions of occasional defense with a high traction drive. We’re running a much more conservative 9 (standard TB to 6" wheels after friction losses) primarily because of the balance.

We’re not planning on any robot-on-robot defense, however we play more of an indirect defense. And when we are robot-on-robot, we have a specific area and position to play from, which will greatly assist our allies, and hinder the opposing team. No more info on that, though. :wink:

I would say that gearing fast is not particularly a problem. In straight pushing matches gearing fast will just result in a stall out, even if the other robot is geared much much slower, they wont really back-drive your motors, and as long as you have grip nothing really happens. Our 2011 robot was geared 14.4 ft/s and was able to play effective defense because it had slightly better acceleration than a standard AM shifter drive-train and it could just stay in the way. Even against teams with lower gear ratios such as 5 or 6 ft/s any direct pushing match usually just ended in a stall out because we had enough grip and back-driving motors is incredibly difficult.

TLDR; Grip is more important than gear ratio as far as pushing matches go.

Check out JVN’s Design Calculator. It hasn’t been updated with 2012 motor data but it is still one of the best resources for drive train calulations. You should be able to check what your top speed was on your robot from last year by putting in all the numbers.

Also here are theupdated motor specsfor this year (as of 1/16/2012).

For what’s it’s worth we’re gearing for around 10-11ftps this year.

thanks. We’ve been using JVN’s Design Calculator.

Still no specs for the Fisher-Price FP-000968-9013.

Does anyone have data or manufacturer specs for the FP-9013??
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My gut says 12ft/s is fine.

We’re gearing for 5.5/14.5ft/s