FRC 95, The Grasshoppers, Build Thread
 

Super-duper late start this year, but here we are!

We took a more 'main stream' approach this year than in many past years, but of course we had to make a few things a bit different.

Chassis is our normal plate-spacer-sheet metal construction with live axles connecting 10 6in wheels (colson for now, pneumatic maybe later... if we ever get them!) 6 CIMs geared for 10.4ft/s (ish) single-speed with WCP gearboxes.

Our main mechanism is a shoulder-mounted shooter/intake combo with two stages of belts/pulleys and rollers. The shooter is powered by 4x 775 pros, and the shoulder is controlled with 2x mini-cims.

Almost everything will have encoder feedback. An ardupilot will assist with navigation, and an Axis camera will assist with vision processing and/or manual aiming.

Firstly, here is a CAD cap of our 2016 robot: Kovaka



(I don't have a lot of great piece-part mfg steps, apologies)

Here is the plasma-cut blank of our belly-pan.



We then bent that in-house into the crazy belly pan shape for our chassis.



And have started to build the shoulder rail assembly, which is a major structural element in the chassis. Although the chassis is (on purpose) a bit flexible to give us a little pseudo-suspension.



I will try to get a few shooter pictures and other layout pictures tonight.

I have left our numerous details and design choices, but feel free to ask if anything piques your interest.

Re: FRC 95, The Grasshoppers, Build Thread
 

Thank you for doing this again, its one of my favorite build season threads. Glad its back.

Re: FRC 95, The Grasshoppers, Build Thread
 

Are those 775s 1:1? I can't tell if that middle stage is a planetary or an integrated encoder. If it is an encoder, won't you be exceeding the maximum rpm for velocity control?

Re: FRC 95, The Grasshoppers, Build Thread
 

Beautiful CAD (as usual!) I have a few questions:
It looks a little too tall, but is it low-bar capable? I can't quite tell from the picture.
Are you planning to climb? What defenses can you break?
Are you worried about the whole thing racking under impacts?

Re: FRC 95, The Grasshoppers, Build Thread
 

Nice metal origami work on that belly pan! Looks like you didn't put in the holes with the plasma cutter, do you do them afterwards with a drill press / mill while the part is still flat, or after you bend it to match the holes to the other pieces?

Re: FRC 95, The Grasshoppers, Build Thread
 

The 'booster' stage of the shooter is 1:1 on 775s. Our software/controls team advises me that the Talon SRX input can handle something above 100krpm with those encoders. I didn't do the math myself though.

Thank you!

We intend on being low-bar capable. The shooter folds into the chassis.

No climbing right now, unlikely to add it.

We plan on breaking low bar, ramparts, rough terrain, cheval de fries (sp?), moat, rock wall, sally port, portcullis (sp?), and to hold down the drawbridge for another team to quickly defeat.

All critical motion elements are isolated from chassis twisting, and the top/bottom of the shooter can handle a lot of misalignment with respect to each other. Think more gumby and less he-man :)

Thank you! It was an interesting project, but all very doable with the right press-brake. We only played the aluminum drums on a few folds (brought the fold to 70-80deg on the brake and hammered them home).

For 'critical' plates like the drive pod plates we blank out the part on a CNC plasma cutter and then do all of the holes/fine features on a Prototrak CNC knee mill. For less critical items like the belly pan we will pierce all of the holes with the cnc plasma cutter, then slice the part out (still on the cnc plasma cutter).

I know the picture of the first belly-pan blank shows no pierces, we made a second pan with hole pierces and match-drilled the holes into that first blank by hand.

Re: FRC 95, The Grasshoppers, Build Thread
 

Also, without electronics, our chassis is coming in at 65lbs.

Our shooter structure is coming in at 13lbs (no motors/shafts/pulleys/belts).

We anticipate being around 100-110lbs fully dressed.

Re: FRC 95, The Grasshoppers, Build Thread
 

I think they missed a decimal place. The table in section 7.5.4 of the Talon SRX Software Reference Manual states that the CTRE Magnetic Encoder has a maximum RPM of 10,000.

The 775pros have a free rpm of 18,730. Even if you're running at 75% free speed, that's still over 14,000 rpm.

Re: FRC 95, The Grasshoppers, Build Thread
 

Thanks for the info Ty. We clearly worked the problem from the wrong direction. Hopefully we can come up with a decent way of solving this issue!

Re: FRC 95, The Grasshoppers, Build Thread
 

Just replace the dipole magnet in the encoder with a monopole magnet. That should increase the functional rpm of the encoder by a factor of 2. :P

/s of course

Re: FRC 95, The Grasshoppers, Build Thread
 

I'll do that right after I collect my Nobel prize. ;)

In seriousness, we're likely going to pull the magnetic encoder and use a Grayhill 63R instead.

Re: FRC 95, The Grasshoppers, Build Thread
 

This is looking really good!

Are those semi circle slots in the drivebase for chain tensioning?

Re: FRC 95, The Grasshoppers, Build Thread
 

Woah, that looks awesome! It also looks quite strong. Good job guys!

Re: FRC 95, The Grasshoppers, Build Thread
 

Thanks!

Winner winner, chicken dinner. I'm going to post a picture of our chain tension cams tonight.

Thank you very much! Watching the chassis flex +/- 3 or 4 inches per side, then restore to 'level' is... unnerving, but it works!

Re: FRC 95, The Grasshoppers, Build Thread
 

Picture of our chain tension cams. I'm told they look like ninja ghosts...



... kissing ninja ghosts.

A shot down the inside of a drive pod.



Mini-cim shoulder drive setup. We're gearing 108:1 with the versa planetary (if memory serves) with an additional 16:34 sprocket reduction. Should be able to flip Kovaka back on his wheels if things go sideways... err.. upside down.



Wiring is starting to get laid out. We invested heavily in electronics tools and components this year, and it's paying off. No way we could package 12x speed controllers into this belly pan so neatly if we were using old-school victors/talons/jags. Also, we love velcro.



Starting to populate the shooter with axles, belts, and pulleys.

Re: FRC 95, The Grasshoppers, Build Thread
 

A close-up of the shooter.



It's a bit... different... than most shooters we've seen before. We've setup the first 'booster' stage (3/4 of the length) to ramp up in speed as it feeds into the 'firing' stage, which spins considerably faster. Prototype testing has been quite promising.

Re: FRC 95, The Grasshoppers, Build Thread
 

A few pictures from today:

The shooter is nominally populated with belts and rollers and stuck on the robot!



How he'll be able to fit under the low bar.



Wiring is about 70% there, enough for a power-up test!



We're currently trying to get code on the Athena (we refuse to call it the "Roborio"), which always seems to have some growing pains. We'll get there...

Re: FRC 95, The Grasshoppers, Build Thread
 

Make sure you take into account the load guides for the versaplanetary. This gearing ratio is either just barely scraping by or it is outside of recommended loading.

Re: FRC 95, The Grasshoppers, Build Thread
 

Are you planning to intake from both sides? Is there any significant advantage, that your team saw, to that strategy (if you are indeed capable of intaking from both sides)?

Re: FRC 95, The Grasshoppers, Build Thread
 

We did use the guide. We are right on the edge of what is advisable for the versaplanetary with a mini-cim. During normal operation we will be nowhere near the stall limit of the mini-Cim. Flipping the whole robot back over will only be a 22amp draw (from JVN) design call.

Though your point is well-taken. The versaplanetary guide is to be taken quite seriously!

Re: FRC 95, The Grasshoppers, Build Thread
 

A team after my own heart.

Re: FRC 95, The Grasshoppers, Build Thread
 

Man, I love 95's robots. You guys always put out something beautiful and unique.

Re: FRC 95, The Grasshoppers, Build Thread
 

I love seeing this thread every year. 95 is always evolving and improving. Good luck in 2016!

Re: FRC 95, The Grasshoppers, Build Thread
 

:)

Thanks! That means a lot to us. It is something that our founding mentors believed in strongly.

Thank you! It is what we strive for, at least in baby steps. And good luck to the Rocketeers!

Re: FRC 95, The Grasshoppers, Build Thread
 

RE the dual lock on the electronics - you sure that'll hold everything tight when crossing defenses?

Looks good again this year man.

Re: FRC 95, The Grasshoppers, Build Thread
 

We are not sure yet, definitely going to test it thoroughly. We do have some contingency plans if it doesn't work though. The wiring is secured in a few key locations aside from the Velcro.

And thanks!

Re: FRC 95, The Grasshoppers, Build Thread
 

Wow, that's a really creative design in a game with many similarly designed low bar bots. We'll be seeing you guys at Granite State, good luck!

Re: FRC 95, The Grasshoppers, Build Thread
 

Started our drive-train burn-in only to have the burn-in go a little too literal for us...

Side plate off to investigate:



Yeah... had some rubbing chain tensioners...



Milled them down, reassembled, and tried out some defenses.

Moat

Low Bar

Did some crossing exercises, everything looked good, until...



Weirdest chain failure I've seen, and the only one I've ever had on a 95 robot. Master-link was good, fractures are on opposite sides of the chain loop, tensioners were installed and slack(ish), and our nominal FoS is around 4 or 5. Bizarre...

Re: FRC 95, The Grasshoppers, Build Thread
 

The shooter is now wired up and functional!

Here is the firing stage of the shooter spooling up to full-speed. It is powered by 2x RS775Pros with 1:1 versa planetary transmissions. All belts are designed 'perfect' center to center. Shafts are 1/4in steel D-shafts supported by bearings rated to ~50krpm.

Kovaka firing stage spool-up

Here is a test shot with the booster stage feeding the firing stage.

Kovaka test shot

Two of three subsystems down... only the shoulder to go...

Re: FRC 95, The Grasshoppers, Build Thread
 

Sweet!

Re: FRC 95, The Grasshoppers, Build Thread
 

When I showed this video to my father (Lewis Sussman, he was our head coach for a few years back in the mid 2000's), his response was (and I quote!) "It sounds like a giant hive of killer bees!" :D :yikes:

Re: FRC 95, The Grasshoppers, Build Thread
 

FTFY :D

Re: FRC 95, The Grasshoppers, Build Thread
 

"A plague of [killer robot] locusts o'er the land!" :D

Re: FRC 95, The Grasshoppers, Build Thread
 

This was my biggest concern, along with cracking wheels, when designing this year. I would suggest getting a lot of spares for competition. Going over the obstacles and slamming into the ground will definitely break chain, as you saw first hand. At least it happened now and not at a competition.

Re: FRC 95, The Grasshoppers, Build Thread
 

What about slamming down causes chains to break in your estimation? (I mean this as an honest question, not a sarcastic one)

Re: FRC 95, The Grasshoppers, Build Thread
 

(I added the '.' to the tags)

Getting an 'about:blank' on this URL. Looks like a vBB IMG tag is embedded inside the URL tag. The IMG tag links to the picture just prior to the link. The other youtube link works fine though.

Re: FRC 95, The Grasshoppers, Build Thread
 

Fixed, thanks. Clearly clicked the "image" shortcut when I meant to click the link shortcut.

Re: FRC 95, The Grasshoppers, Build Thread
 

When pivoting on a wheel, driving, and slamming down on the ground with 120+ lbs will exert huge amounts of not only tension, but shock to the chain. There were times in 2012 where teams that went over the middle bump would shear a chain link after slamming into the ground. This is especially prevalent with #25 chain used on drive wheels.

That is my understanding and experience (wheelies in 2013 broke our chains sometimes), if I'm not completely right, sorry.

A way you can help prevent it is by switching to #35 chain, but honestly, just bring 5 or so spare chain lengths to competition (just in case).

Re: FRC 95, The Grasshoppers, Build Thread
 

Interesting. I believe your empirical evidence for sure, and we always bring an extra 25ft spool of chain and dozens of master links! Cheap insurance...

Re: FRC 95, The Grasshoppers, Build Thread
 

Last night we got our shoulder joint hooked up, but found that we couldn't hold tension properly in the chain, so we'll be working to improve that tonight.

We also got our long-awaited pneumatic wheels in, which helped immensly with crossing barrier like the rock wall.

However, we snapped a chain again! :eek: I re-did my tension calculations and found that I had made a mistake and that our FoS was not 4-5 ish, but closer to 1.8! That's no good, clearly. So, we'll be upgrading to #35 chain for our drive.

Pictures and video to follow.

Re: FRC 95, The Grasshoppers, Build Thread
 

It's been a long couple of days...

Re-chained our drive pods with #35 chain in a night. Remarkably we were able to make everything fit.



We discovered that some spacers had been installed improperly, which likely contributed to chain breaks, but installed the #35 chain anyway as insurance.

We did a bunch of driving around and everything went smoothly for once! We're able to conquer the low bar, moat, rock wall, and rough terrain (all in low-friction flavors).



Our "W-Drive" is proving to be quite smooth over a variety of obstacles. It seems to be effectively mixing the great carpet performance of Colsons with the good cushion of pneumatic wheels when going over obstacles.

On the other hand we've blown up a couple welds, thrown tons of belts, and are just starting to work on PID drive/arm tuning... so... it's going somewhat rough at the moment, but are working to correct as much as we can as quickly as we can.

Going on hour 11 today... wish us luck!

Re: FRC 95, The Grasshoppers, Build Thread
 

I'm sure James is totally burnt out after this weekend, so I'll post a quick update- after a monumental final push (just under 12 hours on Saturday and another 9 on Sunday :ahh: ) by our heroically dedicated students and coaches, we've ironed out most of the last bugs and wrinkles with our design. We have now successfully tested and proven functionality on all of the static defenses, ball pickup, and ball shooting! Of course, anyone who's done this before knows all too well that a robot build is NEVER "finished", so we'll likely be tinkering and tweaking right up to the last minute before bagging and tagging, but things are definitely looking good.

Most of what's left is code and drive practice, and our crack programming team is chugging away on drive tuning, vision, auto move, and awakening sentience in our maniacal artificial intelligence (It's passed a turing test, now we just need to implement the "Destroy All Humans" protocol, currently it's stuck on "Annoy" instead of "Destroy" >_< )

Last bit of good news for now, we had a friend of the team who's previously acted as an inspector at competitions come in and give us a going over, and we've passed robot inspection with flying colors!

I'm sure once James has awoken from his coma he'll be back to post pics/vids and to chime in, but for now good luck to all and see you at the competitions!

Re: FRC 95, The Grasshoppers, Build Thread
 

An end-of-build update.

We bagged a nominally functional robot. All of our features work, except for vision tracking (due to inadequate LED illumination, mostly).

Here we are testing with a ring light that did illuminate well enough, but did not package well into the robot.



Down the mouth of the beast. You can see all of the belts and rollers, running on 1/4in D-shaft with set screws. The surgical tubing in the back bowing in the side-panels is absolutely key to our consistent shooting. It centers the ball in the back of the shooter and prevents any drag from the sides on the ball as it exits the later stages. It acts like a funnel of sorts. The barber poles help ensure that balls enter the shooter/collector properly and prevents the ball from rolling belts off of their pulleys.



Crossed a lot of defenses to work out our #35 chain upgrade and get a little driver practice in. Also, we are doing header preservation with an ardupilot, so the driver pulls the joystick trigger and the robot keeps itself going straight. A nice little aid for crossing.



Disclaimer: we generally include our b-roll stuff rather than editing down to the highlights/best performance. Partly because editing video takes time, and partly because it can be disheartening to compare ones own holistic experience to another teams' highlights.

Some videos:

Self-righting with the arm.

The magic of the W drive! Here's the rock wall.

One shot from shooter consistency testing. We just skim the 8-9ft ceiling at roughly 20ft range, landing at about 30ft.

Crossing the moat/trying to get stuck on the moat. We can come to a complete stop anywhere on the moat and either back out and/or continue through.

Crossing the ramparts would be easier if we made sides for the defenses... I think we'll do okay on a real field. Note: heading preservation was NOT working for this trial :D

I don't have a good video for the rough terrain, but we can drive over, and even turn, on it without issue.

Overall... a long build season for the Grasshoppers, but a rewarding one. We got way outside of our comfort zone on a lot of different aspects of this robot. But, that's how you grow! We look forward to competing with our fellow NEDErs in Windham, UNH, and UMass!

Re: FRC 95, The Grasshoppers, Build Thread
 

One of our programming coaches has come up with an interesting side-project he calls Pit Hub. He has setup a wired network using a Raspberry Pi to run Git Hub in the pits, so programmers can operate as normal at competitions. I'm excited to see how it stream-lines our competition coding efforts!