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 I'm sure you can come up with something, with a bit of warped thought!
... and if not, warped thinking is what your team's Engineers are for! :) - kmcclary [more] |
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A pet project of mine that began in 2012 when the competition drivetrain used by team 766 was almost a complete failure. That year, the team used a 6wd where the center wheels on each side were not driven and actuated down by pistons to allow for turning (or at least that was the idea). It did not work particularly well, as the turning ability of the robot was terrible with the center wheels down, and near non-existent when they were up.
After almost two years of thought and multiple design iterations, this is what I have come up with. It is a 6-wheel drop center drive when the pistons are retracted, and 4wd when extended. The pistons are 1-1/4" bore bimba pistons with a fail-safe return spring so that if pneumatic pressure is lost, the robot remains functional.
No one I know has build, is building, or has plans to build such a drivetrain. I did this as a CAD and design exercise.
Discussion
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20-02-2014 18:49
TheMadCADer
Re: pic: Grasshopper Drive
I've seen a few drivetrains like this, notably in 2011 when 33 and 1477 each used some type of it (and just so happened to form an alliance at Championships that year). I'm sure there are more out there, plus you can also look at Butterfly drive designs since the principle is fairly similar.
For info on 33's version, check out their white paper as well as their CAD and code. It's hard to notice in their build video, but it's there if you look.
For 1477, I don't think there is much more available than what I could see in their build video (but there are plenty of shots of it in there). James Tonthat would be the person to ask for more information on it.
20-02-2014 18:50
xXhunter47Xx
Re: pic: Grasshopper Drive
I've actually been thinking about this but with a WCD that deploys omni/mecanum wheels and detracts the drive wheels to allow strafing.
I think the free rolling of the center wheels caused it to be bad, have you thought about incorporating it with motors?
20-02-2014 19:29
wilful
Re: pic: Grasshopper Drive
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Originally Posted by xXhunter47Xx
I think the free rolling of the center wheels caused it to be bad, have you thought about incorporating it with motors?
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20-02-2014 19:31
Chris is me
Re: pic: Grasshopper Drive
I would be very worried about side loading on the modules. With modules that long, you run significant risk of deflection under load and thus throwing chains, damaging parts, etc.
Parallel plate drivetrains can be a good choice if you have the right combination of resources (or rather, lack thereof), but just know that you end up using a lot of material in the axis you don't need it. Your strength is going to come from your standoffs. If you have any way to add flanges (e.g. making this out of C-Channel) it will add to rigidity substantially. This is especially important on the drop down wheel.
I would significantly reinforce the drop module and shorten the moment arm (try having a pair of sprockets idle on a shaft close to the wheel, that lets you shorten the module without breaking center distances). If you can add some mechanism to transmit side loads through the chassis (i.e. delrin guides physically constraining the module), all the better.
The integrated piston support is rather cool, but not a super efficient use of resources. You end up using more than twice as much material that just ends up being wasted.
20-02-2014 19:37
Electronica1
Re: pic: Grasshopper Drive
I am going to leave this here.
Also, from the cad, it looks like you could take an AM14U and adapt it to this design by adding the lever arm and also adding a piston mount. It would save you time and money over constructing your own sheet metal frame.
20-02-2014 20:00
wasayanwer97
Re: pic: Grasshopper Drive
Looks nice, although I'm not convinced of the practicality.
(Not to discredit the design. Practicality is subject to resources anyways.)
I spent a lot of time this year practicing plate drives myself, and nothing like his ever occurred to me.
A few questions/concerns though:
First, (though pardon me if I missed something, I'm only learning too) I can't really see the advantage of this over a normal, drop center, 6 wheel. It seems like there may be a lot of complexity and use of resources that might not provide an equal return in performance. What is achieved by going from 6 to 4?
Second, you might to want to lighten those plates, as there's a lot of unneeded material in that plane. Structure optimally comes from profile, not thickness. And in this case, as previously mentioned, it's going to be the standoffs that provide most of your support.
Also, already mentioned before too, but having separate plates that you bolt/rivet on for your piston support would save a lot of metal.
Looks cool altogether though. I'd love to see where this goes.
20-02-2014 20:12
Chris is me
Re: pic: Grasshopper Drive
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Originally Posted by wasayanwer97
First, (though pardon me if I missed something, I'm only learning too) I can't really see the advantage of this over a normal, drop center, 6 wheel. It seems like there may be a lot of complexity and use of resources that might not provide an equal return in performance. What is achieved by going from 6 to 4?
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20-02-2014 20:27
wasayanwer97
Re: pic: Grasshopper Drive
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Originally Posted by Chris is me
The huge advantage is that you lose the ability to spin / be spun. This has big consequences in certain games - for example, it's a lot harder to beat an unprotected full court shooter that you can't spin. Breaking through defense in certain scenarios is also easier, since a lot of defense is targeted high speed ramming designed to spin. This is one of the subtle advantages of a butterfly style drivetrain.
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I had noticed that before, but I didn't stop to think of the positive advantages to it. That's a pretty good way to minimize the effectiveness of defense.
Good to know. Thanks Chris!
One more reason to add to my list as to why we'll try a butterfly over the off-season...
21-02-2014 09:32
Peyton Yeung
Re: pic: Grasshopper Drive
45's 2011 robot had the front 2 wheels on a pivot similar to a jaw. When the cylinders were actuated the front 2 wheels lowered raising our center wheels. It saw limited use during competition but it helped with auton. It also helped when we t-boned robots while on d because we couldn't rotate well so they couldn't spin out of the way.
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