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pic: Plywood Butterfly Drive Render
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Re: pic: Plywood Butterfly Drive Render
Is there any reason why you cant shift the colsons closer together and use two pistons between the two sides instead of the four to reduce complexity? Otherwise it looks good although you may find you want to gear it to be faster.
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Re: pic: Plywood Butterfly Drive Render
I would highly suggest you have the traction wheels on the outside and the omni wheels on the inside. We did it like your current setup this year, against the advice of teams like 148, and we regret it. When you shift into traction and want to push you'll tip slightly and end up partially on your omni wheels.
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Re: pic: Plywood Butterfly Drive Render
So butterfly drive is like octocanum with omni wheels instead of mecanum wheels?
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Re: pic: Plywood Butterfly Drive Render
Looks good, I want to see the real life prototype!
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My biggest pet peeve of this type of drivetrain approach will always be that the two CIMs on the front don't contribute much power in a pushing situation. If you are geared to be traction limited, I don't think this is an issue. |
Re: pic: Plywood Butterfly Drive Render
What about arranging the power transmission components like this? (Warning: MS Paint Art):
![]() That would allow all 2 (or 3) CIMs on each side to drive both wheels and move the omni wheels to the inside. |
Re: pic: Plywood Butterfly Drive Render
I like it. I have to ask, does your team have a laser capable of making this? If so, what kind?
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I have been thinking of a way to have the CIMs still face towards the outside of the rail yet recess into that space between the modules and distribute power like your drawing. This year we used the space on one side to hold the cRIO while on the other it was just wasted space. The reason I would want the CIMs to face the outside is it would allow the overall rail thickness to be reduced since it wouldn't have to contain the entire CIM body. |
Re: pic: Plywood Butterfly Drive Render
Here's a 6-CIM version, with the wheels belt-driven from a central gearbox. I did not switch the omni and Colson wheels; the robot has to tilt to an extreme angle for the raised omni wheels to touch the ground. It now has adjusted speeds of 13.8 and 6.9 fps.
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Re: pic: Plywood Butterfly Drive Render
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Re: pic: Plywood Butterfly Drive Render
Looks good! Always love to see laser cut wood construction in FRC. Really like the 6 CIM setup with the reversed gearbox. Lot more open in the middle than a lot of octocanum and butterfly designs. With the 6 CIM layout especially, I would recommend flipping your wheels so that it pivots about the traction wheel rather than the omni. Doing this prevents the module from being side loaded when pushed sideways in traction mode.
Have you considered using pancake cylinders for module actuation to save some space and weight? |
Re: pic: Plywood Butterfly Drive Render
Looks great! In addition to the above (swapping wheel placement), I think you could get a more compact design using four fat pancake cylinders instead of four longer cylinders with a long lever arm on the butterfly. You're losing a lot of pod-turning torque based on that angle anyway, so why not mount a pancake cylinder so it can push the pod straight down?
(We've been iterating octocanum for quite a few years now, and that's how we intend to do it this year if we keep octocanum this year...which we may not.) |
Re: pic: Plywood Butterfly Drive Render
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I noticed a few problems with my design that I also need to fix in the next iteration: the belts to the modules run into the bellypan, the bolt that serves as an axle for the gearbox is not adequately supported and the bottom two CIMs in each gearbox can't be installed or removed once the chassis is assembled. |
Re: pic: Plywood Butterfly Drive Render
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Re: pic: Plywood Butterfly Drive Render
If it simplifies the design, you could consider the option of using shifters for the central gearboxes rather than a pulley reduction between the traction and omni wheel. That way, you can shift from high speed to high torque independently of which wheels are on the ground and pivoting about the traction wheel isn't a big hassle. However, this is added complexity.
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Re: pic: Plywood Butterfly Drive Render
It's great to see another team going with this method of construction. Mine has been doing laser cut plywood chassis in the past two years, and we love it.
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Re: pic: Plywood Butterfly Drive Render
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It's hard to find high-quality information about wood chassis in FRC since so few teams have used them. |
Re: pic: Plywood Butterfly Drive Render
How are the cut plywood pieces of your frame and wheel assemblies attached together? Are you using a glue? Or are there tiny screws?
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Re: pic: Plywood Butterfly Drive Render
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Re: pic: Plywood Butterfly Drive Render
![]() Here's my progress on the next iteration of the drivetrain. The chassis will be sturdier when complete, but the module and powertrain are just about done. Currently, it weighs 30.5 lbs (the same as the original 4-CIM version). Improvements in this version include: -Simpler and lighter powertrain due to direct-drive gearbox -Stiffer module with less wasted space -Smaller, lighter pancake cylinders for switching between wheels -Narrower side rails and more open bellypan The outside plates will be attached with T-nuts (http://goo.gl/XBWxdN) so they are removable for easy maintenance. |
Re: pic: Plywood Butterfly Drive Render
Here's the more-or-less complete version of the drivetrain, except for the finger joints, which are time-consuming and no fun to draw. Sturdier structure, lightening holes and encoder mounts are added. The pneumatic cylinder mounting is improved.
The two aluminum tubes on top are an example of how a hinged superstructure can be mounted, similar to our 2014 robot (http://www.chiefdelphi.com/media/photos/39338). I'd like to integrate bumper mounts into the wood frame, but am uncertain of how best to do so in a way that is simple, robust and allows for quick swaps. Anyone have ideas? ![]() Unless anyone has ideas for improvement, next steps are probably cutting some test pieces on the laser to learn about best practices for finger joints, large parts and bearing fits before manufacturing a full drivetrain. |
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