22-06-2008 01:17

s_forbes

Re: pic: Stackerbox Mecanum Prototype

Nice concept, I like it! Strong, simple, and easy to maintain... everything you need in a drivetrain. I especially like the use of stackerboxes as transmissions; using only one gear reduction and only one chain reduction should make it nice and efficient.

I'm not sure about the rectangluar crossmembers though... cutting the holes may be a bit challenging. Have you considered using round tubes at all? May make manufacturing easier.

Great design.

22-06-2008 01:20

MrForbes

Re: pic: Stackerbox Mecanum Prototype

or even just a channel across each end, so the frame can flex, since mecanums like "suspension".

I like the idea of using CIMs on stackers, who thought of that?

22-06-2008 16:22

Rupnick

Re: pic: Stackerbox Mecanum Prototype

My only input is that if you plan on using the Andy Mark 6" mecanums I would wait until the redesign is available next yea. 1675 had many problems with them this and Andy said that they are redesigning them to hopefully eliminate most of the problems seen this year.

22-06-2008 20:44

Akash Rastogi

Re: pic: Stackerbox Mecanum Prototype

I agree with that. In Atlanta, Andy said they'd be redesigning to make the wheels stronger. I suggested a smaller size for some of our small class robots as well. Really hope to see those

22-06-2008 20:56

Carlee10

Re: pic: Stackerbox Mecanum Prototype

This might be a stupid question, but what type of metal is the frame made out of?

22-06-2008 22:09

gblake

Re: pic: Stackerbox Mecanum Prototype

JK,

Without an active tensioner, my hunch is that the Stackerboxes will inevitably slide in the directions the chain is pulling them.

I'm guessing that you will need something actively pulling the sliding motors/stackerboxes toward each other to keep the correct tension on the chains; perhaps a spring or one of those gizmos that has an eye bolt on each end and has an oval you twist to move the bolts closer or farther apart.

Also, to avoid having the chain tension creating a moment that wants to twist the shaft the drive sprocket is on, a bracket that wraps around the sprocket and supports both ends of the shafts could be what is at each end of a tensioning system.

Blake

22-06-2008 22:12

MrForbes

Re: pic: Stackerbox Mecanum Prototype

The hardware store guys call them "turnbuckles"



(I know you knew that....)

22-06-2008 22:13

EricH

Re: pic: Stackerbox Mecanum Prototype

Depends on attachment. I've never seen the tensioning method described fail. It's standard Kitbot tranny attachment. Not sure how Stackerboxes attach, but if it's similar, there should be no problem.

22-06-2008 22:41

gblake

Re: pic: Stackerbox Mecanum Prototype

Thank You! - I spent 30 minutes trolling through the (not-so-useful) Lowes web site trying to find/remember that word and avoid having to embarass myself; and I failed

Turnbuckle, Turnbuckle, Turnbuckle, Turnbuckle, ...

Blake

22-06-2008 23:01

s_forbes

Re: pic: Stackerbox Mecanum Prototype

Key word is depends... Our rookie year we used slots in the frame (for the wheel axle bolts) to act as our tensioners, but they always loosened up after several matches. I know this strategy has worked for other teams before, but there was something funny about that first robot of ours...

Also note that the kit bot has an aluminum bracket bolted to an aluminum frame; lots of frictional force! Lexan may not act the same way and might slip, but I don't know for sure. A turnbuckle may be a very good idea! (or one of those cam shaped tensioners, like on the 968/254/60 drive)

23-06-2008 00:27

EricH

Re: pic: Stackerbox Mecanum Prototype

That's part of your problem. I've always seen it with the trannies. 330 '05 had this, with KOP tranny (slots in base plate) attached to the frame with bolts going into slots in the frame.

Also, why would anyone use Lexan as the drive frame? (And don't tell me to see the 2007 design book--that team used a metal frame to support their drive.)

23-06-2008 01:08

JVN

Re: pic: Stackerbox Mecanum Prototype

I believe Team 20 used Stackerboxes for their Mecanum drive this year. It seemed to work out pretty good for them. I may be mistaken though.

23-06-2008 03:05

s_forbes

Re: pic: Stackerbox Mecanum Prototype

I was referring to the lexan part of the stackerboxes, not the frame rails. (as for lexan in drivetrains, you could see 190's robot in 2006 if you want a really neat example )

23-06-2008 03:18

AdamHeard

Re: pic: Stackerbox Mecanum Prototype

I usually wouldn't use a COTS turnbuckle to tension chain as it just seems big and unweildy..... But, if you got one that is about the length between the inner bolts (to the center of the robot) on one stackerbox and the inner on the other, and the eyelets were about the clearance size for a #10, you could tension both chain runs by pulling the gearboxes towards each other.

EDIT: on second thought, get a turnbuckle with plain threaded ends instead. Make a block with a threaded hole for that end on one face, and a clearance hole for a #10 on the perpendicular face (not vertical). Put that block on one of the inner #10s on each of the stackerboxes, and hook up the turnbuckle to them.

23-06-2008 09:21

JesseK

Re: pic: Stackerbox Mecanum Prototype

A steel washer could be put in between the lexan face plate and the frame to create the same frictional force.

Now that I think about it, an aluminum or thick plastic cam as a locking mechanism could be useful once the chains are tensioned and the four transmission bolts are tightened. This may be the simplest and most lightweight option. Cam design is also an area of CAD I haven't explored yet.

As shown & calculated it is 6061 T6 Aluminum. This reminds me, I need to make some adjustments and figure out how the cyllindrical plate spacers can be welded in such a cramped area...any ideas?

For the design I'm not worried about a moment on the output shaft, since such a force is usually the result of overtensioned chains or misaligned sprockets. I'd also like to note that the output shaft is already supported in 2 places by bearings and adding a third support is generally asking for too much complexity. A locking or permanent tensioning mechanism (as you suggested) combined with good build practices should circumvent this concern.

This seems like a great idea, but 1885's recent bad experience with tensioning systems that are dependent upon each other has put a bad taste in my mouth.

If implemented independently, this is probably the best way to deal with tensioning to make it zero-maintenance. I'll experiment with the cam system described above and this one for revision 2.

Thanks for the feedback guys, keep it coming!

03-11-2008 14:58

colin340

Re: pic: Stackerbox Mecanum Prototype

i woul just move the stacker boxs cloeser to the wheel and go with a all gear drive Tran

03-11-2008 20:54

Not2B

Re: pic: Stackerbox Mecanum Prototype

That is an important thing to remember. A little frame flex is a good thing for mecanums. Makes a big difference - at least it did on our '08 robot.

04-11-2008 00:05

AdamHeard

Re: pic: Stackerbox Mecanum Prototype

In this case having chain as the final reduction is a good idea; provides a method of changing the final gear ratio without moving the gearboxes, also the frame can flex/bend slightly and still run.