Build Blitz Robot Reveal - Team JVN

[Grant Cox]

http://content.vexrobotics.com/buildblitz/images/robots/JVN-351px.jpg (http://content.vexrobotics.com/buildblitz/images/robots/JVN-HiRes.jpg)
(click for high resolution version)

After one of the most intense three days of their lives, Team JVN is proud to present their final creation. Features include:


New 2014 Drive in a Day (http://www.vexrobotics.com/vexpro/structure/2014-drive-in-a-day.html) chassis that is now available to all teams, with four omni wheels and direct-mounted CIMs
Launcher with 60 ft-lb of surgical tubing, pulled back by a custom cam actuated radial release mechanism (or "choo-choo")
Optimized shot to score anywhere 7-18 ft from the goal using "Aren's Sweet Spot" (http://www.buildblitz.com/team-jvn-arens-sweet-spot/)
Intake roller using 3.25" VersaWheels and passive side rollers, run by a Mini CIM motor mounted on a 9:1 VersaPlanetary

Check out the official reveal video here: http://www.youtube.com/watch?v=Gm96S8gdhR0

For more information on how this robot came to be, be sure to check out BuildBlitz.com (http://www.buildblitz.com), where you can find team bios (http://www.buildblitz.com/team-jvn/) and a full CAD assembly (http://www.buildblitz.com/final-cad-files/). The mission of Build Blitz is, and has always been, to educate teams on the process these designers went through when designing their robot. As such, check out the liveblogs on the homepage of BuildBlitz.com, and feel free to use this thread to discuss or ask questions about Team JVN's final product.

[Thad House]

You linked Copioli's video in the post instead of JVN's.

But otherwise, I LOVE team JVN's robot. It great, and fairly simple at the same time.

[Grant Cox]

You linked Copioli's video in the post instead of JVN's.

You made it in right before I edited it. Should be fixed now!

[DampRobot]

I have to say, I was rooting for Team Copioli from the beginning, but I really have to hand it to Team JVN. They pulled off an extremely effective robot, even for a six week timescale.

[Ether]

Question. The choo-choo cam appears to be spinning at roughly 5 sec/rev = ~12 RPM. So the BAG motor would be spinning at roughly 5*100*84/18 = 5600 RPM, or 37% of free speed. Is full voltage being applied to the BAG motor?

[Aren_Hill]

Question. The choo-choo cam appears to be spinning at roughly 5 sec/rev = ~12 RPM. So the BAG motor would be spinning at roughly 5*100*84/18 = 5600 RPM, or 37% of free speed. Is full voltage being applied to the BAG motor?




Ether,

That video clip is slowed down, in actuality it take about 2 seconds to reload.
We are giving the BAG full voltage.

[MrRiedemanJACC]

Love the four bar mechanism for getting the reload. Extremely ingenious!

One question though, why did you use omni wheels rather than Mecanum? Was it availability or was it programming (I think I remember you guys using a VEX system, not the C-Rio with Labview) or just easier to do it with Omniwheels?

[Ether]

That video clip is slowed down...

I thought that might be the answer. Your new numbers put the BAG in a happier place on the motor curve :-)

[Aren_Hill]

I thought that might be the answer. Your new numbers put the BAG in a happier place on the motor curve :-)





Yeah, I'm looking forward to next year with the new PD board with current monitoring built in, we did test some with a clamp on ammeter and saw ~12amp peak draw for the windback.

[Richard Wallace]

Thanks for that bit of data, Aren. Seems like the mini-CIM BAG is a bit oversized for this mechanism, electromagnetically speaking. I like that. :]

[Dukenator76]

How are you guys releasing the shooter? I have downloaded your Cad files looking for a way of releasing it from the gearbox or cho-cho? can you please explain.

[Richard.Varone]

Such an elegant design, we'll def be prototyping our own version! Team 271 sends our thanks and can't wait to look at those CAD files :D

[Ether]

How are you guys releasing the shooter? I have downloaded your Cad files looking for a way of releasing it from the gearbox or cho-cho? can you please explain.

http://www.chiefdelphi.com/forums/showthread.php?p=1326068#post1326068

[Thad House]

Thanks for that bit of data, Aren. Seems like the mini-CIM BAG is a bit oversized for this mechanism, electromagnetically speaking. I like that. :]

We are currently looking at testing a choo-choo, and we are planning on using a 775, thru a 63:1 versaplanetary, then a similar 18:84 ratio. At 25 amps, it should spin at about 30 rpms, and pull about 350 lbs at a point 2 inches out from the rotation. Overkill a little, but more speed and power is always the answer.

[Ether]

We are currently looking at testing a choo-choo, and we are planning on using a 775, thru a 63:1 versaplanetary, then a similar 18:84 ratio. At 25 amps, it should spin at about 30 rpms, and pull about 350 lbs at a point 2 inches out from the rotation.

How did you calculate the 350 lbs number ?

[cbale2000]

What did team JVN use for surgical tubing on the launcher (and where do you get it)? The tubing we've been prototyping with has been less than effective.

[Aren_Hill]

What did team JVN use for surgical tubing on the launcher (and where do you get it)? The tubing we've been prototyping with has been less than effective.

Just black Latex tubing from McMaster.
http://www.mcmaster.com/#latex-tubing/=q9fexw

I think that stuff was 5234K46 (1/2" OD, 1/4" ID)

[Ryan Dognaux]

I don't remember seeing this anywhere so I figured I'd ask - what material are the ball holding posts made from and is there a vendor where we could pick up a few?

http://i.imgur.com/jOjffaLl.png

[Aren_Hill]

I don't remember seeing this anywhere so I figured I'd ask - what material are the ball holding posts made from and is there a vendor where we could pick up a few?

http://i.imgur.com/jOjffaLl.png

Ryan,

Those are chunks of McMaster part# 87235K81
We just shoved it over some standoffs made from 1/2" HEX stock.

-Aren

[KevinG]

What material did you use for those flexible black rods?

[Aren_Hill]

What material did you use for those flexible black rods?

1/2" Black Delrin rod, but many things will work, we just happened to have it on hand.

[Dan Oelke]

I love the choo choo. What I don't understand is how you did the pivoting joint between the parts of the linkage. Guessing from the video looks like about 1/4" x 1/2" bar stock and I just don't see how you can do a pivoting link in that 1/4" thickness.

Can you give me any pointers or diagrams or ?? about how that joint is put together.

Thanks!

[Aren_Hill]

I love the choo choo. What I don't understand is how you did the pivoting joint between the parts of the linkage. Guessing from the video looks like about 1/4" x 1/2" bar stock and I just don't see how you can do a pivoting link in that 1/4" thickness.

Can you give me any pointers or diagrams or ?? about how that joint is put together.

Thanks!

In our case I essentially made a shoulder bolt that tightened into the first strap and captured a bushing which the other strap spun on, I "handcrafted" the attachments due to limited time and not having shoulder bolts of the proper size on hand.

[andboyer]

Can someone add a little more detail? The video doesn't explain the details of the release.

[Ether]

Can someone add a little more detail? The video doesn't explain the details of the release.

Look more closely at the bar link that's attached to the cam.

Notice how the protrusion on the cam catches that bar as the catapult is being pulled back.

Notice how, in the video, the cam stops before that bar goes over-center.

To release, the cam is rotated further (in the same direction it was turning before) until the bar goes over-center. At that point, the tension pulls the bar off the protrusion and launches the catapult.

[Willyspu]

On the opposite side of the 84t gear there is a pointer and switch, is this a encoder to hold the motor in the ready position? If not, what is it's purpose?

Thanks,
Jim
Team 2144

[Aren_Hill]

On the opposite side of the 84t gear there is a pointer and switch, is this a encoder to hold the motor in the ready position? If not, what is it's purpose?

Thanks,
Jim
Team 2144

This single switch controls the entire retract and fire mechanism, since the cho cho only rotates once per cycle it is just as easy as running till the switch is hit, then stopping.
When the fire button is pressed the shooter pulses forward for .25 seconds, waits .25 seconds for the action to cease, then runs until the switch is hit again.

I have yet to see a simpler method.

[Willyspu]

What type of switch is this? Is it an on/off, position switch or encoder?

I am a mentor and just trying to figure out how you held the motor in position until you were ready to fire the next shot.

Thanks!

Jim
Team 2144

[Thad House]

What type of switch is this? Is it an on/off, position switch or encoder?

I am a mentor and just trying to figure out how you held the motor in position until you were ready to fire the next shot.

Thanks!

Jim
Team 2144

The switch is just a limit switch that tells the system when to stop turning the motor. What actually stops the axle from backdriving is the wrench in that picture. It is just a standard ratcheting wrench, and you can see it in the picture right below the pointer.

[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?

[D.Allred]

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]

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]

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]

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]

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.