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-   -   Butterfly/ octocanum drives (http://www.chiefdelphi.com/forums/showthread.php?t=129199)

tim-tim 29-04-2014 16:41

Re: Butterfly/ octocanum drives
 
Quote:

Originally Posted by ErvinI (Post 1380532)
I don't remember the terminology too well, but wasn't the 2010 robot a Nonadrive, since it had a ninth wheel that was actuated down to allow for holonomic drive? Their 2011 robot was iirc their first true butterfly after they realized that the ninth wheel wasn't required for basic strafing.

You are correct in the fact that in 2010 it was nonadrive; however if you ignore the 9th wheel (omni in the center) it is an iteration of the drives being discussed.

I think terminology, albeit important, can sometimes limit creativity.

asid61 29-04-2014 19:25

Re: Butterfly/ octocanum drives
 
Thanks for all the replies. I especially enjoyed the Grasshopper drive (I saw that a couple weeks ago) because it seemed very lightweight @ 30lbs. Also, it didn't look like it would take too much effort for even an inexperienced team due to the fact that the amount of lift on the wheels could vary quite a bit.

So it looks like these modules are a little on the heavy side at around 8-12 lbs, maybe 6 or 7 optimized. It looks like these could be pretty useful to us next year in leiu of a heavy swerve. Thank you so much for all the input!

Madison 29-04-2014 19:56

Re: Butterfly/ octocanum drives
 
Our octocanum modules are 5.75 lbs. each. The pneumatic cylinders driving each pod were mounted to the frame and I don't have the weight of each of those handy. We used four, but you could as easily use 1, 2 or 4 as your frame allowed.

Our first octocanum implementation in 2011, itself the first used in FRC, was made entirely in-house and with no advanced machining techniques. It was designed and built in just a few weeks and while heavy, it was very reliable and effective.

Our 2014 implementation is made with sheet metal and that helped us to realize a lot of weight savings. We relied on our experience from 2011 to design and code the drive quickly.

asid61 29-04-2014 20:07

Re: Butterfly/ octocanum drives
 
Quote:

Originally Posted by Madison (Post 1380722)
Our octocanum modules are 5.75 lbs. each. The pneumatic cylinders driving each pod were mounted to the frame and I don't have the weight of each of those handy. We used four, but you could as easily use 1, 2 or 4 as your frame allowed.

Our first octocanum implementation in 2011, itself the first used in FRC, was made entirely in-house and with no advanced machining techniques. It was designed and built in just a few weeks and while heavy, it was very reliable and effective.

Our 2014 implementation is made with sheet metal and that helped us to realize a lot of weight savings. We relied on our experience from 2011 to design and code the drive quickly.

Wow, that's super light! Even with cylinders, I can't see that popping up to more than 7lbs.
We have a sheet metal guy, but CNC is up in the air right now (our local college can only machine on weekends and they like the manuals).

azcalg 29-04-2014 21:52

Re: Butterfly/ octocanum drives
 
I've been looking at octocanum drive trains as well and come up with several designs so far. I found this thread of 2583's design very useful, and there's information about calculating whether or not you get enough force out of your piston to lift the robot. Also, it's definitely possible to make a working design without CNC or anything heavy duty, but you'll probably want to use belts or chains if that's the case, so you can tension out any discrepancies in hole spacing. We've actually already started on a very crude prototype with chains, but we plan on upgrading to gears in the final design.
As for how long it takes to design, I'd say not very long at all, so long as you have a relatively clear picture of how the finished product will look like. And given the many existing designs you can access, that shouldn't be too hard.

cadandcookies 29-04-2014 22:39

Re: Butterfly/ octocanum drives
 
If you're talking about octocanum without CNC, I believe 525 ran a handmade octocanum setup for a few years. Might be worth checking out their CAD files (among other reasons to check out their files-- they have the most detailed modeling I've ever seen from a team).

philso 30-04-2014 14:30

Re: Butterfly/ octocanum drives
 
We built an octanum system without regular access to CNC equipment. I do not recommend doing that unless you have an experienced machinist guiding the manufacturing effort and making sure the parts are being made accurately and consistently.

There are similarities and differences between our modules and the modules that 148 used. Both our modules used one of the axles in each module as the "pivot axle" for the module to move up and down.

In our modules, the pivot axle was a live axle making it necessary to install bearings in the chassis to hold the axle. We also had bearings on the side plates of the module.

In 148's module, the pivot axle was a dead axle so the wheel on that axle had bearings in it. Their module side plates had bearing just like ours. Their pivot axle was screwed into the chassis with a 1/4-20 bolt at each end.

I think our modules had the same number of major parts as 148's modules so the complexity was similar. The big difference was manufacturability and serviceability. Our modules could only be partially assembled before installation. We had to insert the pivot axle, it's bearings, the wheel and all the spacers while it was in the chassis. It took a lot of time and effort to make any changes to the module. 148's could be fully assembled on the workbench and installed into the chassis by screwing in the two 1/4-20 bolts.

Aren_Hill 30-04-2014 18:53

Re: Butterfly/ octocanum drives
 
Quote:

Originally Posted by philso (Post 1381024)
We built an octanum system without regular access to CNC equipment. I do not recommend doing that unless you have an experienced machinist guiding the manufacturing effort and making sure the parts are being made accurately and consistently.

There are similarities and differences between our modules and the modules that 148 used. Both our modules used one of the axles in each module as the "pivot axle" for the module to move up and down.

In our modules, the pivot axle was a live axle making it necessary to install bearings in the chassis to hold the axle. We also had bearings on the side plates of the module.

In 148's module, the pivot axle was a dead axle so the wheel on that axle had bearings in it. Their module side plates had bearing just like ours. Their pivot axle was screwed into the chassis with a 1/4-20 bolt at each end.

I think our modules had the same number of major parts as 148's modules so the complexity was similar. The big difference was manufacturability and serviceability. Our modules could only be partially assembled before installation. We had to insert the pivot axle, it's bearings, the wheel and all the spacers while it was in the chassis. It took a lot of time and effort to make any changes to the module. 148's could be fully assembled on the workbench and installed into the chassis by screwing in the two 1/4-20 bolts.

The 148 module was actually just one long 1/4-20 bolt through a piece of VEXpro tube axle.


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