Fastest drivetrain in Aerial assist?
 

I have been looking at drivetrain designs for next season, and i was wondering: what were the fastest robots in terms of acceleration, and top speed and what drivetrain (Swerve, WCD, tank, etc.) did they use? I believe the fastest team in the PNW was probably Bear Metal team 2046. They used a WCD.

Re: Fastest drivetrain in Aerial assist?
 

Fastest I saw was my old team 1102. They had a 8" wheel mechanum drive that went close to 20 fps. I haven't seen a better implemented mechanum in the south-east than theirs this year.

Re: Fastest drivetrain in Aerial assist?
 

Take a look at team 16, The Bomb Squad. I think they have swerve drive as opposed to a WC tank drive. But in terms of speed and agility, I have seen few robots that come close.

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

I was told 1678 gears for 22fps making them the fastest tank drive I know of. As for omni drives we may take 1st as we use mini cims geared 6:1 on 6 inch AM mecanum wheels giving us a top speed of about 19 fps. It comes in handy when things change and I need to be on the other side of the field. Just keep in mind the higher you gear the slower you accelerate. Also, we found that we would loose rollers on our mecanum wheels at speeds above 15 FPS.

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

[Already answered]

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

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

Re: Fastest drivetrain in Aerial assist?
 

Complete BS psuedo math just to set an upper bound based on energy...

Assume 200 amps of draw for 10 seconds, this drops the battery to about 11V. That's 22 kJ of energy.

Assume the motors + drive average about 40% efficiency from electrical power to kinetic energy of the robot, that's 8.8 kJ.

Assume 68 kg vehicle, and E = .5mv^2, then velocity is 52 feet per second.

You'd require many shifting stages with instant engagement, a friction-less environment (in terms of air drag, etc..), and a much longer field though ;)

Re: Fastest drivetrain in Aerial assist?
 

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.

Re: Fastest drivetrain in Aerial assist?
 

I'm pretty sure the fastest robot that I saw this year was 1986. I wonder if Aaron can give us a number?

Re: Fastest drivetrain in Aerial assist?
 

Not sure who was the fastest out there but 368 was certainly one of the quickest...and nimble too!

Re: Fastest drivetrain in Aerial assist?
 

11 tooth pinion direct driving a 70 tooth gear on a 4 inch blue nitrile wheel. 6 CIMs, no shifter.

(5,310 RPM CIM Free Speed) x (11/70 gear reduction) x (4 inch x Pi wheel circumference) x (1/12 inches to feet conversion) x (1/60 per minute to per second conversion) = 14.56 ft/sec theoretical unloaded speed.

We never measured the actual speed.

Not the fastest out there, but fast enough for our strategies. Having a great driver helps. ;)

Re: Fastest drivetrain in Aerial assist?
 

Interesting. I was more wondering about friction and stuff like that though, because it is (technically) possible to go faster than that using more motors/ power.
But 52fps... my god.

Re: Fastest drivetrain in Aerial assist?
 

Okay, I'll play this game.

d = maximum linear distance robot can travel
μ = coefficient of static friction with carpet
g = acceleration due to gravity

The robot somehow manages to provide a constant force of μgm in the forward direction. It's mass is m, so the robot has a constant acceleration of a = μg. Assuming the robot starts at rest and x(0) = 0, then v(t) = μgt, and x(t) = (μg/2)*t^2. At x(t) = d, the velocity is the largest. Solving x(t) = d for t gives t = sqrt(2d/μg), so vmax = sqrt(2dμg).

Plugging in d = 60 feet, μ= 1.5, and g = 32ft/s^2 gives vmax = 76ft/s. Then either the robot or the field breaks depending on the quality of your bumpers. ;)

I suppose the robot doesn't necessarily have to drive in a straight line though. If the robot spun in a circle for the whole match, then vmax would be μg*(match length). Using μ= 1.5, and g = 32ft/s^2 again, and match length = 150 s, vmax = 7200 ft/s. Although they would probably not continue the match after the sonic boom.