Fastest drivetrain in Aerial assist?

[Rauhul Varma]

We geared our modified WCD to ~24 fps, and measured just below 23fps with encoder data verified with video analysis.

Originally Posted by Rauhul Varma

We geared our modified WCD to ~24 fps, and measured just below 23fps with encoder data verified with video analysis.

How often do you think you reached your top speed in competition?

[Rauhul Varma]

Originally Posted by Andrew Lawrence

How often do you think you reached your top speed in competition?

Maybe once per couple matches, however we did hit ~19 fps all the time. Since our robot was so light (sub 115 lbs fully loaded) acceleration wasn't an issue.

[Jay O'Donnell]

166 was pretty fast. I think I heard 21 FPS but I could be wrong.

[Arpan]

We geared for around 20 fps actual this year (24 theoretical) on a 6 CIM WCD.

I would highly recommend that you spend some time developing nice control software and getting your driver a ton of practice if you plan on going this route.

Split - Arcade drive is IMO the best for this kind of high speed driving.

[themccannman]

We geared for something like ~24 fps, 6 cims, ~90lb robot. Haven't done an actual speed test but it should give you an idea.

254's 2011 robot slipstream was probably the fastest robot in FRC. WCD, only 4 cims, super light.

[T^2]

Originally Posted by themccannman

We geared for something like ~24 fps, 6 cims, ~90lb robot. Haven't done an actual speed test but it should give you an idea.

We did do actual speed tests. Theoretical free speed was 22.8ft/s, actual was 17.1ft/s (~75% overall efficiency). I might have a forthcoming white paper on the analysis I did with the data we collected.

[asid61]

Originally Posted by T^2

We did do actual speed tests. Theoretical free speed was 22.8ft/s, actual was 17.1ft/s (~75% overall efficiency). I might have a forthcoming white paper on the analysis I did with the data we collected.

Wow, you guys seemed much faster than that. Your driver was very good this year.

I think that you can probably gear for like 26fps and put a software limit that can be increased with driver practice. As long as you have a low gear you would be able to stop yourself from getting stalled easily.

[Dunngeon]

Originally Posted by asid61

Wow, you guys seemed much faster than that. Your driver was very good this year.

I think that you can probably gear for like 26fps and put a software limit that can be increased with driver practice. As long as you have a low gear you would be able to stop yourself from getting stalled easily.

ONLY if you have a low gear/two speed gearbox. Your acceleration will be impacted significantly with a top speed of 26FPS, which may mitigate the perceived higher top speed (not useful if you never get there). Personally, I would only design up to 24 theoretical, because beyond that number most drivers seem to struggle controlling the robot.

Top speed isn't the only thing to consider when choosing gear reduction. We factor in Driver Ability, Game Requirements (open field, field with obstacles) , and Robot factors (such as weight) when choosing the reduction.

This year we were geared for 18 FPS, and achieved 16 actual due to a robot that only weighed 107 pounds w/ battery and bumpers. We thought it was a good harmony between speed, and torque (we run single reduction). If we were to run a 2-speed, the actual would likely be bumped up to 18-20 FPS actual because we can now have a low gear (5-9 FPS) for pushing

[asid61]

Originally Posted by Dunngeon

ONLY if you have a low gear/two speed gearbox. Your acceleration will be impacted significantly with a top speed of 26FPS, which may mitigate the perceived higher top speed (not useful if you never get there). Personally, I would only design up to 24 theoretical, because beyond that number most drivers seem to struggle controlling the robot.

Top speed isn't the only thing to consider when choosing gear reduction. We factor in Driver Ability, Game Requirements (open field, field with obstacles) , and Robot factors (such as weight) when choosing the reduction.

This year we were geared for 18 FPS, and achieved 16 actual due to a robot that only weighed 107 pounds w/ battery and bumpers. We thought it was a good harmony between speed, and torque (we run single reduction). If we were to run a 2-speed, the actual would likely be bumped up to 18-20 FPS actual because we can now have a low gear (5-9 FPS) for pushing

Of course, driver training is extremely important. That's why I suggested a software limit for speed at first and later.
Personally, I think the game doesn't matter as much as driver training. The drivetrain should be what the driver can handle; pretty much every game in FRC in the past several years has required speed.

If you used PWM control to the motor, wouldn't it technically accelerate faster with a software limited top speed? If you don't stall the CIMs, that is. I feel like that doesn't work out, but can anybody explain why?

From what I've seen, acceleration can probably be mitigated as a problem with a 3 + 2/3 cim per side gearbox. (heheheh)
Does anybody know what the maximum speed it is physically possible to go on an FRC robot? Assuming you want to drive for 10 seconds before the main breaker blows with a 100lb robot.

[Arpan]

There was an interesting white paper a while back about how acceleration in FRC robots is affected almost entirely by weight and number of motors, and not much by gear ratio. I'll see if I can dig it up.

[Dunngeon]

Originally Posted by asid61

Of course, driver training is extremely important. That's why I suggested a software limit for speed at first and later.
Personally, I think the game doesn't matter as much as driver training. The drivetrain should be what the driver can handle; pretty much every game in FRC in the past several years has required speed.

If you used PWM control to the motor, wouldn't it technically accelerate faster with a software limited top speed? If you don't stall the CIMs, that is. I feel like that doesn't work out, but can anybody explain why?

From what I've seen, acceleration can probably be mitigated as a problem with a 3 + 2/3 cim per side gearbox. (heheheh)
Does anybody know what the maximum speed it is physically possible to go on an FRC robot? Assuming you want to drive for 10 seconds before the main breaker blows with a 100lb robot.

Empirically higher top speed = less torque which in turn = less acceleration because T = I*M*A/R (Moment of Inertia, Mass, Acceleration, Radius)

If torque decreases with the others staying the same, then acceleration must decrease. That's why adding motors increases acceleration, because it adds torque to the drive.

A small piece I found on HP, I havn't checked the math but it seems logical

Originally Posted by BBray_T1296

Fun fact: 6 CIMs at stall consume a total of roughly 9576 watts of electrical power, which is over 9000!


Seriously though, a robot with 6 CIMs under "normal load" output (excluding friction) a total of 2.6 Horsepower, while a 4 Cim drive does just 1.75. At exactly 40 Amps per motor the numbers are (theoretically) 3.86hp and 2.57hp, respectively.

And as everybody knows, power/weight ratio is the most important figure.

[cgmv123]

Originally Posted by Dunngeon

I *think* the reason is because we are power limited by our PDB and Talons to 40 Amps per motor. Thus all the data I have above for Amperage isn't true if the motors will be drawing more than 40 amps, which they are.

Circuit breakers don't limit current. The 40A circuit breakers used by the PDB won't trip for a few seconds at ~100 amps.

[PingPongPerson]

Originally Posted by Dunngeon

Empirically higher top speed = less torque which in turn = less acceleration because T = I*M*A*R (Moment of Inertia, Mass, Acceleration, Radius)

If torque decreases with the others staying the same, then acceleration must decrease. That's why adding motors increases acceleration, because it adds torque to the drive.

Put into HP

The concept here is correct, but T=I*A/R. The formula that really shows the torque-velocity relationship is Power=Torque*angular velocity, where if torque is increased, then angular velocity must decrease assuming a constant power.

[DampRobot]

Originally Posted by themccannman

We geared for something like ~24 fps, 6 cims, ~90lb robot. Haven't done an actual speed test but it should give you an idea.

254's 2011 robot slipstream was probably the fastest robot in FRC. WCD, only 4 cims, super light.

IIRC they were around 110 lbs in 2011 (although I'm remembering that from a while ago), and geared at something like 18fps. I think their 2014 bot was their fastest in recent memory, weighing in at something like 87 lbs and geared at 20+ fps.

While I'm sure they're not the "fastest" robot (in terms of straight line max speed) I've ever seen, 9973 last year has absolutely phenomenal acceleration, great driving, and a pretty fast top speed. I think they'll stick in my mind for a while as the fastest looking bot I've seen.