2775J Mogo Mech

An alternative method of carrying alliance goals

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I think tilting the goal like you do is definitely the move compared to a 4 bar or a horizontal method. It lets you put rings on more easily without deploying a ring stop or anything and like you say in the video, an opponent would have a very hard time clamping on to that goal.

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Nice design. But why did you chose to use a form of pneumatic tilting instead of using a cam. I know cams are normally used for compact lifts and I get that this is an alternative method video, but im trying to figure out the pros and cons of having this compared to a simpler strategy in a previous thread made by 1422_WI

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Cam takes a motor, pneumatics doesn’t :man_shrugging:

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Im starting to think that probably wasnt the greatest question. srry

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Awesome Design, however, do you think this could work with 1 piston, or in your testing, you had to use 2? I was just considering air pressure but I guess since it wont be used constantly during a match it wont really matter.

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Yes, it’ll work with one piston, but only at close to 100 psi. So basically at max psi you get 24 inch-lbs of work out of one piston, and to lift the mogo (the mogo’s center of gravity) up by 6 (ish) inches takes 18 inch-lbs of work. So even if your lift is perfectly efficient it’ll only work down to 75 psi or so. All that is to say you basically need to use two pistons.

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side note you also want to make sure the goal isn’t bouncing up and down when you drive. so I highly recommend not using 1 cylinder unless you are only planning on using it once in a match. even two cylinders need plenty of bands.
Or you could create a lock with the geometry of the lift and cylinders. it would need to lock when the cylinders were pulling up the lift, then automatically unlock when the cylinders fire back to let the lift fall.

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Screen Shot 2022-01-09 at 9.40.43 PM

I am a bit confused on your math and numbers here. The vex page says there is a max force of 12 lb.

Is this a typo(I wouldn’t think so)? So 12lb would have to come from some mechanical advantage that the pistons have? Could you explain the math and numbers a bit more in-depth?

There seems to be some confusion with the units.

The numbers Josh used are in in-lb, a unit of work (not to be confused with in-lbf, a unit of torque). Pounds force is a unit of force. Pounds force (lbf) is what is listed on the vex website.

To get 24 in-lb, I believe Josh simply multiplied the 12lb maximum force by the ≈2” of stroke to get the work.

However- it must be noted that this is an approximation if it is a single acting cylinder. For a single acting cylinder, the force is not constant throughout the stroke due to the return spring, so the maximum work will likely be a good deal less than 24 in-lb, depending on the spring constant.

To find the true work, we would need to take the integral of the force over the length of the stroke. But, for use in vex, this simplification is valid.

For a double acting cylinder, it is my understanding that the force can remain constant throughout the stroke.

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Would it work with single acting Pistons?

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There shouldn’t be a problem adapting single-acting AIR CYLINDERS. The issue is just a direction of force. A double-acting AIR CYLINDER can provide up to 12 lbs in either direction, while a single acting AIR CYLINDER can extend with a force of 12 lbs, but retracts with only it’s internal spring force, which is pretty minimal.

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But he was asking about pistons! :wink:

FWIW, the vex product site never describes them as air cylinders, just cylinders. Despite the nomenclature choice of vex, the items in question do definitely include a piston. IMO, piston is a reasonable way to refer to the item, as that is the moving part.

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The main question I was asking about the single acting cylinders was if the actuation direction could work with this mechanism. This video shows double acting pistons pulling in. So I was wondering if, with the nature of the single acting cylinders only exerting a reasonable amount force by pushing, could they still work with this mechanism? And if so, how?

@2775Josh

You would install the cylinders into the mechanism so that they extend to lift the mechanism.

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As both an engineer and an educator, I think it is important that we teach our students industry standard terms for the components that they use. Those of our students going on in engineering and automation careers will benefit. To someone who works with hydraulic and pneumatic cylinders, referring to a cylinder as a “piston” sounds just as silly as if you referred to a motor as an “armature”

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Thanks for the detail, the armature/motor distinction is apt and clarifies this for me. My background is architecture, not engineering. Rubs me the wrong way when people call joists “beams” and lazy authors call every sort of structural element a “strut.”

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I’m pretty sure this is wrong, even though it doesn’t have a spring as air expands to fill the piston it loses pressure and thereby force throughout the stroke.

But like you said, the approximation is really good enough lol.

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Vocabulary aside, this mechanism is really really simple to build with a double acting piston but a bit harder with a single acting. Off the top of my head, you could make a lever that’s pushed by the piston on the bottom and thereby pulls on the top. Or just use a 1 piston claw 2 piston tilter :man_shrugging:

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I initially thought so too, until I reread what I wrote and looked it up

http://www.gearseds.com/files/Pneumatics_Sample_Lessons.pdf

All four of these sources mention constant force for a double acting cylinder, although I’m not confident in how applicable (or relevant) it is in vex

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