FRC 95 The Grasshoppers 2019 Build Thread


#81

We have thought about it and are not planning on using any springs. Reducing strain on the motors is not needed in our experience from last year.


#82

Do you need to apply power to the motors so they elevator will wont fall down?
Last year we used a worm gear for our elevator but this year we have decided to use planetary because its way more efficient. What is the gear ratio on your winch? Does the elevator fall down under its own weight when the motors are not powered?


#83

Yes, we will stall our winch motors to hold elevator position. We are planning on 2x 775pros, reduced 16:1, turning a 1in diameter winch drum, and controlled with a VersaPlanetary mag encoder. This is identical to our setup from last year, just packaged differently. The elevator will fall down when the motors are un-powered.


#84

Saturday was a big assembly and fab day. We started with this:

And ended with this:

Things are pretty cramped, but we’re getting it all fit in. We’re really digging on the snap-in wire track and our CANBus block (lower right of the picture above). This lets us use a parallel CANBus network and not a daisy-chained one, significantly improving network impedance. It still lets us replace devices one at a time, and removing a device and doing no other actions keeps the balance of the network intact. It also gets the robot down to two primary terminations: Power Pole and Weidmuller ferrules. Feels nice to simplify!

Our shop’s CNC mill is down for the count: severe corrosion on the Y-axis servo connections. So @Andy_A and I are going to have to mill all of our elevator bearing blocks in my garage (which is also a fab shop business we run). We might look for a machining sponsor that’s not us for next season.

I fat-fingered a few things in CAD and we’re going to have to make things work. I mixed up the battery width and height, which is an easy-ish fix. Our brake cylinder mounts don’t line up with the clearances cut in the brain pan. Not sure how we’ll fix that one…

We have started laying out two mechanisms to add HAB 2/3 capability, but don’t have it put together enough for a cohesive story without a lot of hand waving. You can check it out in our OnShape directory if you’re so inclined.

Edit: we are starting with assembling our competition robot this year, with the practice robot to follow.


#85

Do you have a link to the wire track and CANBus block (or some more info)?

Also, how is servicing electronics and fixing wires with most of the components on the bottom of the eboard? My team has always had all of our electronics on the top of our eboard. Have you had issues with things becoming loose on the field or wires disconnecting? What made you put things on the bottom?


#86

Biggest inspection problem we ever had was mounting the PDB upside down so that it wasn’t ‘easily accessible’ according to the head robot judge.


#87

Your inspectors and FTA’s will appreciate that wire track too, such an improvement to easily following wires and inspect terminations when they are neatly routed, protected, but still visible.


#88

Here is a link, we repurposed a 2-pole power distribution block.

Having things upside down has made service relatively easy because there are no mechanisms in the way. We have not had any electrical connections come loose, but we did lose a compressor on a practice robot that wasn’t bolted down (just wood-screwed). Putting things on the bottom protects them from game pieces, enables access without reaching through mechanisms, and creates more electronics/penumatics room. It also lets junk fall out of, rather than in to, any of the electronics.

We will have some stuff on top of the brain pan, like the Athena and radio, that need routine access.

This was not a problem for us last year. -shrug-


#89

Thanks for the info!


#90

Working on a toggle lock mechanism for part of our HAB 3 climbing mechanisms. I think we finally have something sorted that will package well and eliminate the need for extra-beefy air cylinders in this application.


#91

I think I follow what you did there… and if I did, I’m excited to see it work.


#92

Last night @Andy_A worked in my garage/a shop we run together to machine our elevator bearing blocks because our build space’s CNC mill is down for the count with some nasty corrosion.

Getting there…

Assembly continued on our competition robot, we hope to be driving the chassis tonight. Feels later than other years, I just hope we have enough time to get good practice in.


#93

That board is looking very nice. What are you using to secure your battery (given that it seems like it’s going on the bottom of your board)?


#94

Thank you!

https://www.mcmaster.com/3955t284 in the 2in wide variety. It worked well for us last year for the same purpose of strapping in the battery upside down.


#95

Progress has been made on our toggle-lock skids for the HAB 3 climb. They will likely be a combination of plasma cut aluminum and laser cut delrin.

Only one is roughed into the robot model right now, but the snazzy mates in OnShape mean that it articulates as we intend it to!


#96

Love the idea! Over-center 4-bars are tons of fun!

I assumed the 4 vertical cylinders were for getting onto the second level, so will you need them given you can use the same system to get you onto the second HAB level?

After getting my bearings with the onshape mate system, it’s really, really simple, and very powerful. It definitely takes some un-learning, and then re-learning to get everything to work correctly. I’m still often frustrated with, “Groups,” and how they prevent updates on the top level unless you suppress and unsuppress, but practice makes perfect. Also, I wish there was a way to align a mate without first creating a correctly aligned mate connector, but I understand why they do it the way they do.


#97

Thanks!

The 4x vertical cylinders are brakes. They will help keep us from being pushed when we’re trying to score. We are likely only to wind up with 2x.

I have rarely needed to make my own mate connector. The ‘reorient secondary axis’ option, and alignment toggle, have solved 99% of the alignment issues I have had with mates.


#98

The reorient function only works in 90 degree increments. The align secondary axis is what i was referring to by creating your own mate connector. That either precludes making the mate you want in the orientation you want, or you have to edit the created mate connectors after the fact. It’s just more clicks than I would prefer.


#99

I got ya now.


#100

I hope you’re not planning on using Chrome to display the camera stream to the drivers - it adds a noticeable delay as compared to Shuffleboard

The Ligerbots did a nice experiment to measure the differences in this thread: