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-   -   Mecanum Differential Drive (http://www.chiefdelphi.com/forums/showthread.php?t=122139)

BBray_T1296 23-11-2013 20:46
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by Oblarg (Post 1305030)
I am quite sure that omni wheel is 4'', with a 72-tooth VexPro gear on it; vexpro does not sell gears that are that size proportional to a 6'' omni.
But VexPro is going to unveil its new products soon, which should include this tiny devil

Oblarg 23-11-2013 20:48
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by BBray_T1296 (Post 1305032)
But VexPro is going to unveil its new products soon, which should include this tiny devil
Yeah, I know, I mentioned it earlier. That should make octanum quite a bit easier to realize.

Quote:
Originally Posted by MichaelBick (Post 1305031)
VexPro doesn't sell a traction wheel smaller than 4" either
It is very easy to make your own small traction wheels out of delrin and plaction tread; I've seen several teams that did this.

DampRobot 23-11-2013 20:49
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by AdamHeard (Post 1305019)
Our variant of this was trivially different (biggest difference was using 2" tall tube versus 3") and I can confirm it was easier to manufacture than our WCDs. There just aren't a lot of parts.
Are they really quicker/easier to make? At this point you essentially do a COTS everything WCD, whereas the butterfly, you have to make the plates for the wheels and mill the tubing. I'd also expect that WCDs are a lot harder to get wrong than butterfly drives, at least for most teams.

Of course, basically all drives in FRC (except possibly swerve) are to the point where they work quickly and well 90% of the time. It's funny to think just a few years ago just driving around the field was considered something to be proud of.

AdamHeard 23-11-2013 20:53
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by DampRobot (Post 1305035)
Are they really quicker/easier to make? At this point you essentially do a COTS everything WCD, whereas the butterfly, you have to make the plates for the wheels and mill the tubing. I'd also expect that WCDs are a lot harder to get wrong than butterfly drives, at least for most teams.

Of course, basically all drives in FRC (except possibly swerve) are to the point where they work quickly and well 90% of the time. It's funny to think just a few years ago just driving around the field was considered something to be proud of.
It was a loaded statement I suppose, as we haven't run a WCD with a COTS gearbox yet. That certainly brings it to be more comparable.

If we do WCD again next year, we'll be sticking with our bearing blocks. If we also purchased COTs blocks it makes the drives pretty comparable.

With our router in house the butterfly side plates are very fast to make.

AdamHeard 23-11-2013 20:59
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by MichaelBick (Post 1305043)
I know for sure that those are the sizes of the wheels(6" mecs, 4" tractions). We are pretty good friends with 973, and as Adam said, they are an running almost identical drive to 3928.
Sorry buddy, but it's 4" Omni w/ a 64T gear and a custom plastic wheel at ~ 2.4" Tread diameter. :(

For the sake of completeness, the pulley ratio from omni to traction is 18:30.

Oblarg 23-11-2013 21:05
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by AdamHeard (Post 1305047)
Sorry buddy, but it's 4" Omni w/ a 64T gear and a custom plastic wheel at ~ 2.4" Tread diameter. :(

For the sake of completeness, the pulley ratio from omni to traction is 18:30.
Oh, it's a 64t? Do the 72t gears have ground clearance problems, or did you just want it to run faster? I ask because I had been previously advised that 12t pinion on a 72t gear with a 4'' wheel ends up at 16 fps and works well.

Quote:
Originally Posted by MichaelBick (Post 1305048)
I mean omnis, but looking back, it does look like you are correct. I'll delete the post just so it doesn't confuse anyone
Fair enough, I'll do the same.

AdamHeard 23-11-2013 21:08
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by Oblarg (Post 1305051)
Oh, it's a 64t? Do the 72t gears have ground clearance problems, or did you just want it to run faster? I ask because I had been previously advised that 12t pinion on a 72t gear with a 4'' wheel ends up at 16 fps and works well.
I believe, but am not certain, that 3928 ran 12:72 (15.5 fps free speed).

We ran 12:64 (17.4 fps free speed) because we like things faster in California.

The extra ground clearance is a bonus. Even with the 64T a lot of crud was sucked into the gears.

Oblarg 23-11-2013 21:09
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by AdamHeard (Post 1305053)
I believe, but am not certain, that 3928 ran 12:72 (15.5 fps free speed).

We ran 12:64 (17.4 fps free speed) because we like things faster in California.
Cool, thanks for the info.

4464 currently has 12:72 for our offseason butterfly design, which is basically that but on a standard c-base frame and with delrin side-plates (the only CNC machining we have ready access to is a lasercutter at UMD). Might consider changing to 12:64 in later iterations if the ground clearance is a problem.

Aren_Hill 24-11-2013 20:57
Re: Mecanum Differential Drive
 
Quote:
Originally Posted by AdamHeard (Post 1305053)
I believe, but am not certain, that 3928 ran 12:72 (15.5 fps free speed).

We ran 12:64 (17.4 fps free speed) because we like things faster in California.

The extra ground clearance is a bonus. Even with the 64T a lot of crud was sucked into the gears.
We had no issues with the gears being that close to the ground, for reference

And 973 was driving underweight which helps a fair amount.

Also Californians are weird.

-Aren


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