Build Blitz Robot Reveal - Team JVN

[D.Allred]

Originally Posted by thesuperfez

I have a question about the piston used to extend the rolling arm that collects the ball. We are a rookie team and are unsure of the sizing of pistons. Does anyone know the bore size and stroke length used for this bot in particular?

Looks like a 3/4" bore, 8" stroke. The build team could verify. However, they are also using surgical tubing to help balance the weight of the arm when extended.

Eagle Robotics (team358.org) has the most comprehensive FRC resources I've found. There is a great paper on pneumatics on this page.

http://www.team358.org/files/pneumatic/

Good luck with your rookie season!

David

[thesuperfez]

Thanks for all of the help

[Jay Trzaskos]

Just a note on the intake actuation, those pneumatics were used out of necessity as we had a very limited choice or bore and stroke length of which we had two identical cylinders. These specific cylinders are far from the ideal, and can be changed in order to achieve far better mechanical advantage.

Jay

[thesuperfez]

Originally Posted by Jay Trzaskos

Just a note on the intake actuation, those pneumatics were used out of necessity as we had a very limited choice or bore and stroke length of which we had two identical cylinders. These specific cylinders are far from the ideal, and can be changed in order to achieve far better mechanical advantage.

Jay

We are looking to build a very similar mechanism to the arm used in the JVN bot, and dont really know too much about pneumatics. Could you tell us what the optimal bore and stroke length would be? or if anyone could explain what these things do and what they affect so that we can figure it out on our own.

[BJC]

Originally Posted by thesuperfez

We are looking to build a very similar mechanism to the arm used in the JVN bot, and dont really know too much about pneumatics. Could you tell us what the optimal bore and stroke length would be? or if anyone could explain what these things do and what they affect so that we can figure it out on our own.

Without knowing your arm's geometry or weight it is difficult to recommend a optimal bore or stroke length.

The first thing to think about is levers. If you look at the JVN intake from the side it is basically a stick on a pivot-- a lever. A door is also a lever. If you push on the door close to the pivot point it requires much more force than if you push close to the doorknob. The same goes for the intake - the further out from the pivot you attach the pneumatic cylinder the less force you will need to move the arm.

The other factor is the angle that you push at. When you push on a door you are pushing roughly perpendicular to the surface of it. The closer you get to pushing perpendicularly to the lever the less force it will take. Think of the JVN intake in a side view again. Draw a stick version of it on paper if that helps. Draw a dot where the intake pivots, where the pneumatic cylinder attaches to the intake, and where the pneumatic cylinder connects to the chassis. You should form an angle. The closer that angle is to 90deg the less force it requires to move the arm.

That should give you a baseline to create your own setup. The JVN robot used 7/8" bore cylinders which were overkill. If you stick with that bore and keep the above two paragraphs in mind your final design should definitely have enough force to go up and down with some gusto.

Cheers, Bryan

[paulonis]

How did you attach the 84t gear to the hex shaft for the choo-choo? Pretty clearly no room for a hub or a snap ring. Did you "glue" it with loctite 638 or something like that?

[wajirock]

Originally Posted by paulonis

How did you attach the 84t gear to the hex shaft for the choo-choo? Pretty clearly no room for a hub or a snap ring. Did you "glue" it with loctite 638 or something like that?

We are wondering this too. Does anyone have any information?

[Arefin Bari]

If you looks closly on the release video, it looks like they have tapped some holes on the gear and used some button cap screws to hold the gear in place.

[Kellen Hill]

Aren had told me the other week that they milled a couple of grooves into the face of the gear (after milling the face of the gear flat to avoid contact with the choo-choo linkage). They then drilled a hole through the hex shaft and used a roll pin to retain the gear by using the grooves milled into the face of the gear.

[Aren_Hill]

Originally Posted by Kellen Hill

Aren had told me the other week that they milled a couple of grooves into the face of the gear (after milling the face of the gear flat to avoid contact with the choo-choo linkage). They then drilled a hole through the hex shaft and used a roll pin to retain the gear by using the grooves milled into the face of the gear.

Yup, milled the boss flat, then put a roll pin through the end of the HEX shaft ~1/16th from the end. Then just milled a flat pocket just wide enough and deep enough to completely hide the roll pin.

With access to more screw sizes I likely would've just drilled and tapped the end for a large countersunk screw that was over 1/2" diameter to retain it.
A snap ring and counterbore would also work.