FRC971 Spartan Robotics 2016 Release Video

[MichaelSchuh]

Originally Posted by Travis Schuh

We had a mixup when putting the file on the server and got the wrong extension on it. The file was saved as step, you should be able to open it fine if you rename the extension to .step. We are working on getting the version on the server fixed. Sorry for the inconvenience.

The CAD now downloads as a STEP file. Sorry about the mistake.

Michael

[thatprogrammer]

Wow, there are a lot of details about this robot that I hadn't noted previously! I have a lot of questions based on the cad I looked at, but I'll post the main ones here:

• What is the purpose of the sideways mounted 775 pro gearbox near the gearbox that actuates the intake up and down? I see it appears to drive some sort of bar near the drive train.
• How did you achieve such smooth motion on the up and down movement of the intake despite it only being powered on 1 side?

Thanks for releasing your cad! The level of detail and compactness found on this robot has left me speechless.

[Travis Schuh]

Originally Posted by thatprogrammer

Wow, there are a lot of details about this robot that I hadn't noted previously! I have a lot of questions based on the cad I looked at, but I'll post the main ones here:

• What is the purpose of the sideways mounted 775 pro gearbox near the gearbox that actuates the intake up and down? I see it appears to drive some sort of bar near the drive train.
• How did you achieve such smooth motion on the up and down movement of the intake despite it only being powered on 1 side?

Thanks for releasing your cad! The level of detail and compactness found on this robot has left me speechless.

That gearbox is our hanger winch. One end of the string went there, the other was tied on the other side. That way we didn't have to have a winch gearbox/line centered on the robot and got a 2:1 reduction out of the pulley.

The 2" tube welded solidly to the 1x2 in the intake adds a lot of stiffness. Also, we motion profile the intake so that will reduce the torsional load across the intake.

[thatprogrammer]

Originally Posted by Travis Schuh

That gearbox is our hanger winch. One end of the string went there, the other was tied on the other side. That way we didn't have to have a winch gearbox/line centered on the robot and got a 2:1 reduction out of the pulley.

The 2" tube welded solidly to the 1x2 in the intake adds a lot of stiffness. Also, we motion profile the intake so that will reduce the torsional load across the intake.

Thanks for the answers!
One additional question: What prompted you to switch to chain drive this year?

[Travis Schuh]

Originally Posted by thatprogrammer

Thanks for the answers!
One additional question: What prompted you to switch to chain drive this year?

The 5mm GT2 belts and #25 chain have comparable load ratings. To use a belt in the same application would require a huge sprocket, which would be heavy, wide, and require a lot of custom work. Much easier to buy stuff that is designed to bolt together.

[Michael Hill]

I love the use of an actual ratcheting wrench....and the billion 775pros.

Also, I'm curious...what is the Encoder Shielding Chassis Ground Assembly for?

Finally, what went into the design decisions of making your own gearboxes versus using something like the VersaPlanetary on some subsystems (like your intake)?

[frcguy]

Thank you guys for releasing everything! Hopefully we can take a look at all of it and learn from the amazing things you guys do.

Originally Posted by kevincrispie

The pictures can be viewed on the team Picasa page, in folders marked "2016".
https://picasaweb.google.com/117769834305511597729/

Also, happy to see you guys got some photos of when our team visited!

[AustinSchuh]

Originally Posted by Michael Hill

Also, I'm curious...what is the Encoder Shielding Chassis Ground Assembly for?

In 2014, we had a lot of trouble with EMI and cross-talk on the robot. Since then, we've spent a lot of time and energy worrying about EMI. We run a 6 pin shielded cable for our encoder and pot combo (ground, power, index pin, A, B, and pot value). To properly terminate the shield, you need to ground it to your frame in such a way that the EMI actually makes it to the frame. That assembly does that.

We had a number of pinched wires this year, so we'll be looking at revisiting that design. You'll see something like that on our robot next year though.

Originally Posted by Michael Hill

Finally, what went into the design decisions of making your own gearboxes versus using something like the VersaPlanetary on some subsystems (like your intake)?

Aren keeps trying to get us to run VP's in places.

We've designed enough custom gearboxes that they aren't risky, and we can generally get exactly what we want when we design our own.

For the intake, we've gotten really good at timing belt reductions, and the single reduction from there would have been required anyways since we needed to power the gearbox from the middle of the shaft anyways. The VP wouldn't have actually made it much simpler.

For the arm (intake up/down, shooter angle, and shoulder angle), we wanted to control the backlash. The backlash at the end of the arm is about 1/16th of an inch, which is phenomenal.

We were actually really trying to use a VP for our climber, but we couldn't get the packaging to work

We've been running timing belt reductions as the first stage since 2013, and have really liked it. They are much quieter, and we don't see wear.

[aphelps231]

Would someone be willing to speak a bit on how power is managed and brownouts are prevented on this robot? Maybe it's a non-issue, but with the amount of motors on the robot and the large forces they (seemingly) must endure, it seems some kind of smart power management would be necessary.

Maybe the answer to this is related to that of the above, but what drove the decision behind which reductions and how many motors to put on each gearbox?

This bot has truly gotten me excited to play with big machines and improve my CAD skills in college. I'm shamelessly jealous of how much 971's students must get to learn about machining and design before they even graduate high school.

[Max Boord]

Any plans to release the cad of the first generation intake? It had some cool sheet metal features I would like to look at.

Also what performance gains (if any) where found by switching the drive and intake wheels for worlds. I had heard that they where switched for weight but the intake appeared to be a little faster at centering the ball as well.

[IKE]

I too am very interested in the brownout management.

I noticed looking through the pictures that you started out with a significantly different collector. Judging by the complexity and completeness of the robot, it looks like a pretty late switch to the mecanum style collector. If you could share your reasons and methods, I would love to hear them, and I think a lot could learn. I know I watched videos of your 2012 collector several dozen times a few years ago. Still one of the faster collector/sorter/columnizer mechanisms I have watched.

[AustinSchuh]

Originally Posted by IKE

I noticed looking through the pictures that you started out with a significantly different collector. Judging by the complexity and completeness of the robot, it looks like a pretty late switch to the mecanum style collector. If you could share your reasons and methods, I would love to hear them, and I think a lot could learn. I know I watched videos of your 2012 collector several dozen times a few years ago. Still one of the faster collector/sorter/columnizer mechanisms I have watched.

I'll answer your easy question first and come back to the other ones when I'm not working.

Our initial intake worked well on the bench when prototyped. We tried lifting/lowering the rollers by an inch on the bench, and it seemed to work "ok". When we finally built it, we learned that pneumatic tires bounce even more than we thought, and we would drive up on balls too easily. That was compounded with it being heavy (~16 pounds), and a bit slower than we wanted. The weight was causing the chain to stretch way too fast and even start to yield when we were going over the bumps. (We learned this year to run 35 chain in more spots). It all added up to an intake which wasn't what we wanted.

There was a video floating around somewhere on CD in like week 4 of a mecanum intake which worked, but wasn't as fast as we knew that it could be. That, the sheer simplicity of it, and 118 shipping with one made us switch over immediately after ship. We slapped together a prototype on our practice robot, worked out the ideal roller placement, and then built it. It took us a little bit over a week to pull the whole thing together from design to full implementation. It was during that time that we learned that a traction wheel in the middle would cause it to jam, but an omni wheel in the middle let it center nicely as the ball was coming into the robot. We figured that out by pulling dozens of balls into our prototype and high-speed videoing it while trying to jam it. Unfortunately, this meant that we needed a separate CDF/Portcullis mechanism, since our old intake could open them, which added more mechanisms and complexity.

I think it was very effective and we will consider doing something similar in the future. I liked our 2012 intake slightly more than this one, but I really can't complain. 2012 (which I saw a number of teams do variations of) would have required some crazy folding geometry for going under defenses. There were very few times when we contacted a ball but didn't grab it.

[MichaelBick]

Whats the purpose of have two different encoders in this gearbox:

[Greg Woelki]

Will a 2016 code snapshot be released as in years past?

Originally Posted by MichaelBick

Whats the purpose of have two different encoders in this gearbox

Possibly for some sort of clever backlash management in code, but you should obviously wait to hear from a 971 member.

[AdamHeard]

Originally Posted by MichaelBick

Whats the purpose of have two different encoders in this gearbox:

The one on the left is a potentiometer (and do to limited # of turns has to be near the output).

The one on the right is an encoder. I know 971 goes out of their way to eliminate backlash as much as possible (like custom sized hex shafts), so putting it earlier in the reduction yields higher resolution (traded off against backlash, which in this case is minimized).