Re: Gearing for 20 FPS?
 

You're dead on Brando. Check out their 2008 video: http://www.youtube.com/watch?v=6fLf71xlVhE

Looks like 148 could've risked rolling over at 30fps, they were getting up on two wheels (Maybe one? Don't know how a 3WD swerve handles) during hard cornering.

Re: Gearing for 20 FPS?
 

You don't need 30 FPS for a slightly longer than 5 second lap without traffic.

Speed Racer, still my favorite robot. A perfect example of KISS. Don't even touch the trackball and score more points than 90% of hurdlers.

Re: Gearing for 20 FPS?
 

Maybe someone's already done this, but here's my quick attempt at the math.

Re: Gearing for 20 FPS?
 

Our 2008 lapbot was geared for 23 fps and had very good acceleration. 4 cims, 70 pounds, 6:1 ratio from CIMs to 6" wheels.
http://www.youtube.com/watch?v=52PxEzpm9Us

Re: Gearing for 20 FPS?
 

I can vouch for that, speedy little bugger

Re: Gearing for 20 FPS?
 

That's 23 fps at CIM free speed. Do you know what was the vehicle's actual top speed? (I'm trying to get some data on realistic numbers for speed de-rating)

Re: Gearing for 20 FPS?
 

6 motors geared for 20 fps will draw a LOT of current at stall (when starting, pushing, or turning in a skid steer arrangement). More than I'd want to design for; you risk resetting the cRIO (if you use the original 8 slot model) or the wireless gaming adapter due to momentary drops in supply voltage when drawing 600+ amps of current. You will then be sitting lame on the field for 20+ seconds while the component reboots.

With 4 motors, 20 fps will result in a woefully slowly accelerating bot.

Both of the above statements assume a bot at or near the weight limit plus bumpers and battery - obviously, a robot that weighs 80 lbs soaking wet can be geared faster and still accelerate at a good clip (although since it is soaking wet, maybe not). Maybe those crazy Cheesy Poof guys who design ridiculously fast welterweight bots are on to something :cool:

Re: Gearing for 20 FPS?
 

Frankly, the easiest way to reach >= 20 FPS is, besides throwing on more motors, NOT approach the 120lb weight limit (which, when adding in the bumpers and battery, goes to the limit of about 150 lbs). Since F=MA, and V=int(A(t),t), Shaving 20 or 30 pounds would be a huge boost in acceleration, and thus make it possible to reach those speeds within the length of the field.
Taking our 2011 robot as an example, it only had sprockets+CIMple boxes as a reduction, while weighing about 110 pounds competition-ready, it accelerated faster to higher speeds than our similar robots in the past that hit the 150 pound mark, but had higher reductions to get similar acceleration up to their lower max speed.

Re: Gearing for 20 FPS?
 

If you open up the question to bots that are geared fps free speed, it's not terribly uncommon. Our 2011 comp bot had a free speed of 20.6 fps, and our 2011 prototype Emperor Swerve was geared for 20.7 fps.

Frictional losses obviously bring these numbers down.

Both these robots have shifting to provide a low gear, and our comp bot was somewhat underweight and had very little friction in drive.

Using the oldschool version of JVN's design calc with the drive modeling tab allows you to graph the position and it's derivatives over time, and study what changing mass, friction, power, gear ratio, etc... has on them. It's very interesting how a *slight* friction difference can change speed appreciably.

Re: Gearing for 20 FPS?
 

Sorry no measurements. With a #25 chain directly from each CIM to each dead axle wheel, and its light weight, the friction loss was very low.

Re: Gearing for 20 FPS?
 

I just looked at this spreadsheet and I must say, I am floored. As a student who knows very little about DC motor physics (or physics in general), I am amazed at the amount of work that went into creating it. I would be interesting in reading an explanation of some of the math/concepts behind it, if someone would know where to find it. Also, if anyone has any tips on using it now that the motor and gearbox scene is slightly different from where it was in 2004, I would definitely appreciate that too.
Well done JVN, it would be cool to see some of these features re-incorporated into a later iteration of the design calculator.

Re: Gearing for 20 FPS?
 

2016's 2008 robot, with an ackerman steering module, there are pictures on CD somewhere of the module.. was set around 21 ft/s, we never got to measure the actual speed. Also I would look at 102's robot from 2008 they had a really fast robot as well.

we were running somewhere between a 6-7:1 gear ratio on two cims with 6" wheels. Pretty controllable for lapping, outside of lapping it was like driving a car, literally. we actually set that robot up with a steering and pedals to make it easy to drive and handle on the field...

heres one of the matches: http://www.youtube.com/watch?v=g58N0...eature=related

Btw, this is a full 120lb machine a little more with the bumpers and battery. i think we recorded 13 laps at chesapeake in one of the matches.

20ft + is not undoable in FIRST, controlling it is the hard part. One of the only reasons we were able to control ours was because of the ackerman steering and running laps being the objective. (steering was favored to help turning left).

Re: Gearing for 20 FPS?
 

btw here is the ackerman module...

http://www.chiefdelphi.com/media/photos/31565