pic: Octocanum Module

[wmarshall11]

[cdm-description=photo]42251[/cdm-description]
1x CIM, 1x MiniCIM

[zinthorne]

Why 2 cims per module? Do you need that much power? The mecanems lose a lot of traction.

Also, are you planning on running 4 of these sets? That is 36 pounds spend on a drivetrain which is a decent amount. Where are you planning on mounting the piston?

[cad321]

How do you plan to actuate it? 2 pistons? 4? And as zinthorne asked, how do you plan to mount the pistons from the chassis to the modules?

[wmarshall11]

Why 2 cims per module? Do you need that much power? The mecanems lose a lot of traction.

It's actually a CIM and MiniCIM, and I'll edit the description to reflect that. I've added that information to the initial post, but can't seem to edit the phot description

This was mostly done as an exercise in how aggressively an octocanum module could be built, and I grafted on the MiniCIM both to see if it could be done and so that a drive using this could hold its own against some of the more powerful tank drives I've encountered.

Also, are you planning on running 4 of these sets? That is 36 pounds spend on a drivetrain which is a decent amount.

No doubt. That's the reality of CIM + MiniCIM + 4x2 Colson + 4" Mecanum. They're not light parts.

Where are you planning on mounting the piston?
How do you plan to actuate it? 2 pistons? 4? And as zinthorne asked, how do you plan to mount the pistons from the chassis to the modules?

The most convenient point from which to rotate the module is the uppermost standoff, so the piston should be mounted there.
The specced safety factor is for a single 2" bore piston per side spanning between modules, a la 1086's Legendairy Drive.

[Electronica1]

You could try to make that colson wheel smaller to save some weight. My team is running an 8 motor octocanum that is about 34 lbs including the entire frame by using 2 inch colson wheels.

[zinthorne]

You could try to make that colson wheel smaller to save some weight. My team is running an 8 motor octocanum that is about 34 lbs including the entire frame by using 2 inch colson wheels.

If he went with a 2 inch colson, he may not be able to fit his gear size onto the shaft without it hitting the ground.

[Chak]

If he went with a 2 inch colson, he may not be able to fit his gear size onto the shaft without it hitting the ground.

But at the same time the gear size would have to be smaller to keep the same speeds, because the wheel is now smaller.
Then again, 2 inch hex bore colsons don't exist anyways. :p
Switching to 2.5 inch colsons could save a few pounds.

[wmarshall11]

Going from one 4x2 to two 2.5x1.25 Colsons would save 0.4lbs per module on wheels. Probably a little over a half pound per module with resulting gearing changes.

[wilsonmw04]

why articulate the motors? It would seem simpler to just move the wheels and leave the motors stationary.

[Electronica1]

Going from one 4x2 to two 2.5x1.25 Colsons would save 0.4lbs per module on wheels. Probably a little over a half pound per module with resulting gearing changes.

Plus, the module itself gets smaller.

[GeeTwo]

why articulate the motors? It would seem simpler to just move the wheels and leave the motors stationary.

To do that, you'd have to drive the articulated wheel from the pivot wheel. This would mean either adding belt/chain or an intermediate gear that would engage both the gear on both wheels. To keep the speed ratio spread, you might need three such gears.

Since the force to articulate the wheels has to be sufficient to lift the robot, the extra amount necessary to move the motors is insignificant.

[Kevin Leonard]

I really like how compact this is. I would be wary of running 8 motors in a drivetrain. It's altogether too easy to draw too much current, especially in traction mode, and trip breakers. Teams that ran 6-8 motors this year didn't have that problem because there was no defense and no pushing, but I know a few teams personally we worked with who had that problem in 2014 and even 2013.

[Nathan Streeter]

Very innovative design; I don't think I've ever seen something similar!

The design seems generally very good. Obviously you have a pretty high weight per module, but it's not bad at all considering you have a mecanum, 2" wide colson, all your gearing, and a CIM and MiniCIM. You could easily drop MiniCIMs on the front or something like that to save an easy ~5 pounds on the robot. I'd say to keep the 2" colson... if you're bothering to have a high-torque traction mode, I'd say don't skimp on it. Now, a fair question could be, "how much do you really need the traction mode?" I think many teams (my own included) tend to want to add all the 'bells and whistles' without really doing the strategic game analysis.

My one comment about the integrity of the design is about the idler axle. I've never used a single bearing on an axle like that... does anyone else have some experience with an idler shaft with gears on each side supported by only one bearing? You could always put a .875" press fit on the back side so you could put a turned down shaft through through the module if you need more support. Seems like 3/8" aluminum would be more than enough for that.

EDIT: I'm guessing you're fully aware, but your mecanum mode is geared pretty high. It may end up working well for you (particularly in some games), but I'd honestly only gear a >110lb robot that high in 2011 and 2014 of the games since 2005 (although I think fair cases could be made for 2006 and 2008). I realize a fair bit of this is a 'strategy/design style' though. :-)

[cad321]

My one comment about the integrity of the design is about the idler axle. I've never used a single bearing on an axle like that... does anyone else have some experience with an idler shaft with gears on each side supported by only one bearing?

I only just noticed this after you pointed it out. I too am interested on what people think about this. On one hand there are so many constraints on the shaft from the meshing gears that it may be alright. On the other hand though, the amount of play in a single bearing (put a shaft through 1 bearing and try to wiggle it up and down) is quite significant.

[fargus111111111]

As far as the idler is concerned, I think it would work but would be quite loud due to almost constant minor imperfections in the meshing.

[nate12345678]

Also, are you planning on running 4 of these sets? That is 36 pounds spend on a drivetrain which is a decent amount. Where are you planning on mounting the piston?

Maybe instead of a colson, you could use a 4" aluminum traction wheel, with tread. From my experience these wheels have a very good traction/weight trade off, compared to most other wheels.