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Unread 29-04-2014, 01:15
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Butterfly/ octocanum drives

So a butterfly/ octocanum drive is where you switch between mecanum and traction wheels, right?
I was wondering what the typical weight and complexity of these systems was. This would be weight per module or, preferably, weight of bellypan + drive base + modules. I have only found one weight listing for an octocanum module, and I think many teams keep the mass under 11lbs.
How long does this take to design? Does this need a particular CNC special part or can it be fabricated with a waterjet/ sheet metal shop?
Any information on these drives would be useful, as I'm looking into different drives for a summer project.

Last edited by asid61 : 29-04-2014 at 01:20.
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Unread 29-04-2014, 01:29
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Re: Butterfly drives

Quote:
Originally Posted by asid61 View Post
So a butterfly drive is where you switch between mecanum and traction wheels, correct?
I was wondering what the typical weight and complexity of these systems was. This would be weight per module or, preferably, weight of bellypan + drive base + modules.
How long does this take to design? Does this need a particular special part or can it be fabricated with a waterjet/ sheet metal guy?
Any information on these drives would be useful, as I'm looking into different drives for a summer project.
Assigning names to a "design" is so limiting. That said a butterfly drive conventionally switches between 4 omni wheels and 4 traction wheels.

I would encourage you to sit down with your team and figure out a list of objectives you would like your summer project to fulfill. Once you've done this I would encourage you to use the chiefdelphi search function to read up on butterfly drives from older threads. Once you understand your design objectives, have an idea of where a butterfly type drive falls on that, and seen a number of designs other teams have already made you can properly assess if you should try to design and build one or if your time would be better spent working on something else. When done properly off season projects can be an extremely valuable resource both in terms of populating your team's design shelf and teaching students. The most important thing is to have a full understanding of why you are building what you are building and how you are trying to improve upon what you have done in the past, have seen others do in competition, or online.

Cheers, Bryan
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Last edited by BJC : 29-04-2014 at 01:41.
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Unread 29-04-2014, 01:40
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Re: Butterfly drives

Quote:
Originally Posted by BJC View Post
Assigning names to a "design" is so limiting. That said a butterfly drive conventionally switches between 4 omni wheels and 4 traction wheels.

I would encourage you to sit down with your team and figure out a list of objectives you would like your summer project to fulfill. Once you've done this I would encourage you to use the chiefdelphi search function to read up on butterfly drives from older threads. Once you understand your design objectives, have an idea of where a butterfly type drive falls on that, and seen a number of designs other teams have already made you can properly assess if you should try to design and build one or if your time would be better spent working on something else. When done properly off season projects can be an extremely valuable resource both in terms of populating your team's design shelf and teaching students.

Cheers, Bryan
Actually, right now it's just me looking at drive train ideas; other people have AP tests to study for right now and just a lot of schoolwork in general. I want to have a list of detailed CAD designs to show the team later once we start thinking about summer projects, so that we can make an educated decision about what we want to try.
I've been cadding only swerve drives and shifting gearboxes up to this point, but I was wondering what I should aim for in terms of weight and size if I CAD a butterfly later.
I want to stick with swerve personally, but the problem is that the programming is very difficult. With a butterfly drive, there is already a lot of programming released, not to mention the programming overall is easier.
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Unread 29-04-2014, 07:43
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by asid61 View Post
So a butterfly/ octocanum drive is where you switch between mecanum and traction wheels, right?
I was wondering what the typical weight and complexity of these systems was. This would be weight per module or, preferably, weight of bellypan + drive base + modules. I have only found one weight listing for an octocanum module, and I think many teams keep the mass under 11lbs.
How long does this take to design? Does this need a particular CNC special part or can it be fabricated with a waterjet/ sheet metal shop?
Any information on these drives would be useful, as I'm looking into different drives for a summer project.
As BJC said, butterfly is [typically] switching between omni and traction wheels; while octocanum is [typically] switching between mecanum and traction wheels.

The main difference between the two are choosing what wheel is opposite of the traction wheel on the pod. While I have not built one, the drives should be slightly heavier than a conventional drive. Majority of these setups use a single gear reduction to the first wheel and then another reduction via chain or belt to the second wheel. This makes up for the weight "missing" from gearboxes.

There are some good examples out there on how they have been constructed in the past. 148 made this type of setup popular in their 2010 release video and their CAD files can be seen on FRC designs and you can see another iteration in their 2011 robot. Another great example is 3847's robot from this year. It was documented fairly well in their build blog. Both of these teams are more than willing to help answer further questions, but these should give you a good starting point. There are plenty of other robots that use these drive types that I didn't mention, these were two I could get my hands on quickly.
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Unread 29-04-2014, 11:58
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If you design an octocanum or butterfly, be ready to spend at least two or three months to go from concept to working prototype. If you use bent sheet metal for your modules you need a water jet, if you use 1/4" aluminum plates, you need a good CNC. Do know that they can be much heavier than other drivetrains depending on their features, so they aren't suitable for some games.
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Unread 29-04-2014, 12:07
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Re: Butterfly/ octocanum drives

Though I doubt it would work with mecanum, we used a new format of the "Tex-Coast Drive," (Grasshopper) essentially combining butterfly with a West Coast drive. We don't CAD nor do we have a CNC machine, so simplicity and ease of construction was something we needed. We built the first prototype and the competition drivetrain both in the same six week build season. It weighs just a bit more than a standard 8WD because of the pneumatic actuation. Here's a link to what I mean: Grasshopper Drive System
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Last edited by Abhishek R : 29-04-2014 at 12:11.
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Unread 29-04-2014, 12:16
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by RobotDoktor View Post
If you design an octocanum or butterfly, be ready to spend at least two or three months to go from concept to working prototype. If you use bent sheet metal for your modules you need a water jet, if you use 1/4" aluminum plates, you need a good CNC. Do know that they can be much heavier than other drivetrains depending on their features, so they aren't suitable for some games.
We went from concept to working prototype in about 3 weeks during build season this year. We didn't do any prototyping or design on that type of drive train before build season started. Do your research and don't be afraid to ask for help. Our drive train wasn't perfect but it did very well and we had to perform very little maintenance on it all season.

Also as noted about it's called Tex Coast Drive now.

There are trade offs in every train and depending on the features you put in it can be lighter or heavier.
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Unread 29-04-2014, 13:22
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by Abhishek R View Post
Though I doubt it would work with mecanum, we used a new format of the "Tex-Coast Drive," (Grasshopper) essentially combining butterfly with a West Coast drive. We don't CAD nor do we have a CNC machine, so simplicity and ease of construction was something we needed. We built the first prototype and the competition drivetrain both in the same six week build season. It weighs just a bit more than a standard 8WD because of the pneumatic actuation. Here's a link to what I mean: Grasshopper Drive System
I had a great opportunity to talk to a couple of people on your team about your drive train, including manufacturing and maintenance. The insight was invaluable. If we decide to do it next year and improve upon it, we'll definitely send you a heads up with any of our new findings. From what I saw it was the best blend of simplicity, maneuverability and immovability. Who knew it was based upon a concept that was put out 3 years ago by the Killer Bees?

The only thing about the whitepaper I don't quite understand is the 'elastic tensioning'. Could you explain?
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Last edited by JesseK : 29-04-2014 at 13:35.
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Unread 29-04-2014, 13:53
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Re: Butterfly/ octocanum drives

As RobotDoktor said, these drives can easily be very complex and heavy. We used it on our competition bot this year, naming the drive base the Dragonfly (And we won Excellence in Engineering at CMP for it). It switches between colsons and mecanum wheels, with each module weighing about 9 lbs. The entire thing with the electrical board, for us, was about 100 lbs packed into 6-8 inches of height. We came so close to the weight budget that we had to cut wires as short as possible just to cut down on weight!
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Unread 29-04-2014, 13:55
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Re: Butterfly/ octocanum drives

A couple years ago our team built a 'slide' drive that used two omni's that were in the middle to translate us and four omnis at the corners to drive. It was terrible, but that's where I first learned of these concept drives.

At the time it occurred to me that you could use something equivalent to a starter bendix drive to push-down the translating wheels only when you need to strafe. In a starter bendix, it moves forward to engage your flywheel using the rotation of the motor--Simple, no space-hogging pneumatics on the frame. I have'nt tried it but I'd be interested Yes, a bendix only moves foreward on one rotation, but I think you could use the concept to design a bendix-in-a-bendix and make one that moves down on both rotations.

And then it occurred to me that this might be better with four-wheels for strafing and four wheels for regular driving . Then I thought why do we even need omni or mechanam wheels for this?

So why does an 'octonum' or any of these others even need translating wheels? If your goal is to strafe, can't you just do that with 'good' wheels?
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Unread 29-04-2014, 14:00
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by hrench View Post
At the time it occurred to me that you could use something equivalent to a starter bendix drive to push-down the translating wheels only when you need to strafe. In a starter bendix, it moves forward to engage your flywheel using the rotation of the motor--Simple, no space-hogging pneumatics on the frame. I have'nt tried it but I'd be interested Yes, a bendix only moves foreward on one rotation, but I think you could use the concept to design a bendix-in-a-bendix and make one that moves down on both rotations.
This sounds quite similar to how the Robowranglers deployed their middle strafe wheel this year.
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Unread 29-04-2014, 14:53
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by JesseK View Post
I had a great opportunity to talk to a couple of people on your team about your drive train, including manufacturing and maintenance. The insight was invaluable. If we decide to do it next year and improve upon it, we'll definitely send you a heads up with any of our new findings. From what I saw it was the best blend of simplicity, maneuverability and immovability. Who knew it was based upon a concept that was put out 3 years ago by the Killer Bees?

The only thing about the whitepaper I don't quite understand is the 'elastic tensioning'. Could you explain?
Quote:
Originally Posted by gotgreen
Apologies that it was not clear. The shifting bearing block is loose on the frame and has to be tensioned. Theraband is connected to the top of the shift plate where the pneumatic cylinder is attached and tensioned to the frame vertically. This seats the bearing block lower lip into the frame when the wheels are up. Also, when pivoting the blocks the chain is loose when up and tight when lowered. Ideally the pivot point should be moved out to reduce this issue. A small piece of theraband can be connected to the bottom of the block and tensioned to the frame. We are not using this. We just attached a small tensioner and it is working fine. The drivetrain complete w/o electronics is right around 30 pounds.
Here you go. And thanks, it was an experiment for us and it turned out pretty well.
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Unread 29-04-2014, 15:02
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Re: Butterfly/ octocanum drives

This year we developed and used a hybrid of an octane. we went with six wheels instead of 8. We used 4 2-stage vex transmissions geared 3:1 and 8:1. We also used a 12 tooth sprocket from the transmissions to mecanem wheels, and then a 22 tooth sprocket on the mecanem. We then moved to a 44 tooth sprocket on the 6 inch wheels. We built two pods for the mecanem and traction wheels duos, and then ran a bar connected to each beneath the central frame of the robot. A 3 inch piston pushed the bar down in the middle of the robot, engaging the traction wheels and lifting the other mecanems in the pod off the ground.

See link for a picture.
http://www.chiefdelphi.com/media/photos/40492

We welded the pods using 1/4 inch bar aluminum. Our frame is made of c-channel. It was not the lightest of drivetrains, but we still fit everything else on the robot with not too much worry about weight.

We could push 90% of the robots on the field, and we could hold our ground against the other 10%.
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Unread 29-04-2014, 15:16
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by tim-tim View Post
There are some good examples out there on how they have been constructed in the past. 148 made this type of setup popular in their 2010 release video and their CAD files can be seen on FRC designs and you can see another iteration in their 2011 robot.
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.
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Unread 29-04-2014, 16:28
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Re: Butterfly/ octocanum drives

Quote:
Originally Posted by ErvinI View Post
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.
I talked about the history of 148's articulating drives, and the evolution of the "Tex-Coast Drive" here:
http://www.chiefdelphi.com/forums/sh...9&postcount=15
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