pic: 6in Butterfly Module With Piston

[Kevin Leonard]

Back on topic and not debating the pros/cons of butterfly vs. mecanum, I have to agree with pmangels somewhat that cantilevering the module sounds quite risky.
I think this would have to be paired with some bulletproof bumpers or an outside rail in order to work super well.

That being said, I love what you're trying to do, and I really wanna see it work.

[wilsonmw04]

How are you going to manufacture the bracket for the cylinder? it looks dove tail joint I would use for wood drawers.

[bkahl]

Originally Posted by wilsonmw04

How are you going to manufacture the bracket for the cylinder? it looks dove tail joint I would use for wood drawers.

It's just a slot that allows the pieces to slide together. The fasteners hold it together, but the slots allow for a strength increase. No crazy manufacturing requirements other than a square hole and square tab.

See the Battlebot Bite Force's construction here

[asid61]

That piston mount plate might bend over time, particularly if there are bumpers contacting it (shoving can get them). We had a similar issue with bumpers in 2014, but it depends on where your bumpers are vertically.

[IndySam]

<Grumpy Old Man Rant>

It's a cylinder, not a piston!

<end Rant>

[Michael Hill]

Originally Posted by IndySam

<Grumpy Old Man Rant>

It's a cylinder, not a piston!

<end Rant>

same. However, to be fair to all "piston" people, if the piston wasn't there, the cylinder wouldn't work.

[Deke]

Some items to ponder on this design, but it looks like you are making progress!



Pic 1:
-The black arrows show close proximity of the standoff bolts, the stiffness gain is minimal, you may consider spreading them around to increase the stiffness or eliminating a bolt from the pairs.
-The blue arrow shows the force applied through the module into the cylinder, and the red arrows are the resulting vectors. This places a moment indicated by the second red arrow and creates a high stress area. Whether the .25" plate will yield or not would have to be determined for the application, but the long mounting point increases deflection and reduces stiffness. This would be unwanted for turning in a tank drive with traction wheels as less stiffness will increase bounce during turning. Stiffness is required to allow the wheels to break traction to scrub smoothly. There are many ways to increase stiffness, Skywalker gave one good solution:

Originally Posted by Skywalkar

[*]I agree that 1/4" thickness on the piston mounting plate (assuming aluminum?) is pretty much necessary the way you've mounted it, but consider what would happen if you switched the mounting plate to the inside of the chassis rail. This would of course require the mounting plate to bend maybe 10-15 degrees outwards to give enough clearance for the piston, but would place it roughly parallel with the piston's stroke; the result would therefore reduce the bending moment on the mounting plate, and let you switch to a thinner material or carve more weight out of it.

Pic 2:
-.25" material is plenty thick to tap, the nuts circled may be eliminated by tapping into the back plate.

Pic 3:
-The blue arrow shows the restriction the .25" plates on the top on bottom rails provide, however, there is no loading in that direction. The bolts also restrain the part for rotational loads. It appears this is an attempt to use the pre drilled holes for assembly, if so, the plates could be removed afterwards to reduce weight and be used as an assembly fixture only.
-The green circles are suggestions for rivet locations. They are lower weight than bolts and easily hand assembled. The rivet holes in the .25" can be laser cut like you want, the plate clamped into position, then the frame rail drilled, and then riveted.
-The red arrow is a suggestion to move the pulley to the outside of the wheels to reduce the bending moment on the axles.

Originally Posted by pmangels17

I'm not going to claim to be an expert on butterfly drive, but I wouldn't feel comfortable cantilevering that module out like it's a WCD, I'd rather support from both sides here. But then again I'm from the east coast...

Originally Posted by Kevin Leonard

I have to agree with pmangels somewhat that cantilevering the module sounds quite risky.
I think this would have to be paired with some bulletproof bumpers or an outside rail in order to work super well.

Do you guys have more information to support these feelings?

[Kevin Leonard]

Originally Posted by Infinity2718

Do you guys have more information to support these feelings?

Nah, I don't actually know how to engineer yet, I only just finished my first year in college!

But great post by you being actually objective!

[Darkseer54]

Originally Posted by Kevin Leonard

I have to agree with pmangels somewhat that cantilevering the module sounds quite risky.

To go against this, I believe 624 said that they cantilevered their grasshopper modules in 2014 without difficulty. Whether the fact that that was a grasshopper rather than full *Octocanum* played into that, I am not sure.

Interesting module, I would also like to see how cantilevering it works out. Make sure you test that before the season starts if you plan on having it as a possibility.

[fargus111111111]

Two things,
First, I too am skeptical of cantilevering the module for stability. I have no doubt that the plates would be fine structurally but I could see where your wheels may want to bend the module and possibly loosen some of the bolts as well as not turn smoothly.

Second, I assume the traction wheels are 3 in, am I right?

I am certainly no expert on this kind of drive and the cantilever may perform wonderfully, I would just have to see in running to be in full support of cantilevering the module. I love the idea behind this sort of drive train and I would love to see a video and real life weight once you actually have it working.

[Madison]

Originally Posted by Darkseer54

To go against this, I believe 624 said that they cantilevered their grasshopper modules in 2014 without difficulty. Whether the fact that that was a grasshopper rather than full *Octocanum* played into that, I am not sure.

Also relevant is which wheel set -- traction or omni -- was on the pivot axle.