Out of curiosity, has anybody actually geared their mecanum drives for anything above 15-16fps? Generally I see speeds of 10-12fps with mecanums.
I’m asking because I always see the claim that mecanums can’t go fast, but I’ve actually never heard of anybody who has tried. There’s nothing that limits it in theory, so I wanted to know the practical limit.
2052 has done a pretty good job of a fast mecanum bot: http://youtu.be/Ogy65hEPIXk
That’s a really well done mecanum. I can’t find the actual speed listed anywhere though, although it definitely looks pretty fast.
At 291 we usually have pretty fast mecanum. We build custom gearboxs and see about 13-14 fps
For a summer project, we built an octanum drivetrain powered off of 4 CIMs and 4 Mini-CIMs, and geared the mecanum wheels to 20.5 FPS free-speed. We saw speeds of about 17 FPS, on the field, and 19 FPS in our school’s hallways.
In addition, we used the OLD Vex 6" mecanum wheels (the ones that break), and still had them last well enough for whole off-season competition. We have since switched to the updated versions, and they look like they should be fine (haven’t tested through a competition though).
WOW see now that’s what I’m looking for! That’s actually a really fast speed for any drive, especially mecanum.
How did strafing go? Even if it was slower than straight, how fast was it? Did you run a suspension?
That’s 93% “speed loss constant” in the hallway and 83% on the field. Interesting.
How did you measure the actual speed? e.g. video, stopwatch, etc?
Would you be willing to share the raw data?
Here’s another one, keep in mind they aren’t on carpet. http://youtu.be/O_vvVU4OBT4
Was this due to never having enough space/time on the field to accelerate to your full speed? That would be a problem this year since the field will get cramped and there won’t be room to accelerate much.
He said 20.5 fps free speed, which presumably meant “vehicle speed at motor spec free speed”. The reduced actual top speed presumably due to JVN’s “speed loss constant”.
Team Titanium’s 2008 robot comes to mind.
I was asking about the difference between the school tested speed and field speed. I’m assuming with a bigger runway one would have more time to accelerate than on a real field that has obstacles.
Pronouns are the cause of many misunderstandings.
The difference in hall vs field speed could be due to the difference in compliance of the flooring (carpeted field vs tiled hallway).
In a frictionless physics lab I would expect the free speed between the field (carpet?) & hall wall (tiles of other hard surface?) to be the same. In the world the wheels may not be perfectly aligned. The macanum rollers turns more freely on a hard surface rather than carpet. All this create side forces. The side forces net out to zero but consume energy thus a lower speed.
Thanks 
Our 2013 robot, Silverfish, used 8" mecanum with a 12.75:1 reduction for a free-speed of 14.53 ft/s (11.77 ft/s adjusted).
Our 2014 robot, Dragonfly, again used 8" mecanum, but with a 10.71:1 reduction for a free-speed of 17.3 ft/s (14 ft/s adjusted).
I wouldn’t.
The compliant flooring (carpet) moves slightly as the mec rolls forward over it, due to the tranverse force component exerted by the roller. This motion is accompanied by roller rotation, which subtracts from forward motion somewhat.
That’s the theory anyway. It would be enlightening to see a controlled test to investigate the magnitude of this effect quantitatively.
did you do any actual speed measurements?
Ether,
Sorry to report we didn’t. These numbers are based on the JVN calculator.
I suspected as much, but hoped otherwise.
We are trying to establish whether or not the 81% “speed loss constant” is a reasonable value to use for mec on carpet.
I agree, this would be great to know. We hold driver practice on competition carpet. I suppose we could mark out the carpet, capture video, and try to get some numbers.