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Unread 01-18-2018, 08:43 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by Cog View Post
By robot sized do you mean smaller wheels? Or did you shorten your prototype to account for the 16" maximum extension?
We made it a few inches narrower, 15in vs 18in, the roller has a shorter pivot arm, 6in vs 8in, and the floor pan is a little thicker. .25in vs .1in. A few other things are a little different i'm sure.

Bad science practice changing multiple variables at once... welcome to build season!
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Unread 01-18-2018, 09:22 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
3. Control your spray environment. Keep dust down, extract paint fumes and over-spray, keep temperatures warm or hot (70-80F+).
I would also recommend wearing a respirator and goggles to catch any stray paint, even with a fume extractor.

This thread has been interesting so far, and I look forward to future progress reports!
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Unread 01-18-2018, 10:16 AM
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Re: FRC 95 2018 Build Thread

Hey James, awesome thread as always.
From your CAD it looks like your elevator is being mounted straight to your bellypan (brainpan?)? Am I missing something?
Also definitely keep us updated on the over-the-top cube collector, because I really like that style and just haven't had a chance to prototype it.
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Unread 01-18-2018, 10:31 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by ctt956 View Post
I would also recommend wearing a respirator and goggles to catch any stray paint, even with a fume extractor.

This thread has been interesting so far, and I look forward to future progress reports!
Yes. Even a 3/4 paper mask does wonders at keeping spray out of your respiratory system. I suggest cleaning safety glasses/goggles with IPA or paint thinner (mineral spirits) immediately after spraying to keep them clean.

Quote:
Originally Posted by Kevin Leonard View Post
Hey James, awesome thread as always.
From your CAD it looks like your elevator is being mounted straight to your bellypan (brainpan?)? Am I missing something?
Also definitely keep us updated on the over-the-top cube collector, because I really like that style and just haven't had a chance to prototype it.
We have not modeled triangulation for the tower yet as it is heavily influenced by the ramp design that is still in progress. We are confident that we can find a solution given the grid of holes on the deck.
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Unread 01-18-2018, 10:54 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
Thanks! You are correct, no drop. We used a flat 6wd last year and absolutely loved it, even geared for 17ft/s single-speed with 6 CIMs. We used Colson wheels, which have a nice rounded edges. I imagine using a flat 6WD with a wheel that has a sharp corner or flange, like a plaction or hi-grip, the edge might dig in and make turning awful.

Credit where it is due: 125 used a flat 6WD in 2014, which gave us confidence to try it, and the FRC Design Calculator Rev 0 was used to calculate turning FoS ahead of testing to make sure that we were not asking for the impossible.
So as a non-mechanical mentor, I didn't know about the FRC Design Calculator. In case there's anyone else looking for it, I think it's available here: https://www.chiefdelphi.com/media/papers/3292
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Unread 01-18-2018, 02:32 PM
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
Yes. Even a 3/4 paper mask does wonders at keeping spray out of your respiratory system. I suggest cleaning safety glasses/goggles with IPA or paint thinner (mineral spirits) immediately after spraying to keep them clean.
Just be sure that your cleaning solution won't affect the structural integrity of the glasses/goggles. My safety glasses once got coated with small spots of paint from an electric sprayer. 70% isopropanol removed the spots completely.
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Unread 01-18-2018, 02:53 PM
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Re: FRC 95 2018 Build Thread

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Originally Posted by ctt956 View Post
Just be sure that your cleaning solution won't affect the structural integrity of the glasses/goggles. My safety glasses once got coated with small spots of paint from an electric sprayer. 70% isopropanol removed the spots completely.
To expand: nearly all safety glasses I've seen/bought/used are made from polycarbonate. Acetone, a common solvent, attacks PC aggressively. IPA and mineral spirits are fine for short-term exposures.
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Unread 01-18-2018, 07:50 PM
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Big Change in Collecting Strategy

Well, we have stopped development on a horizontal roller intake. We got a bunch of materials for the bottom of the intake to test with, and had about zero luck. The big difference we identified with our first prototype, and reproduced with our second one, was the use of a little chain saver on the plastic intake. This isn't legal per the rules (can't contaminate game pieces) and not a great solution besides that.

We did the statics calculations to see what f we would need to prevent binding/tipping vs normal force exerted by the roller... it's not good...



(pardon the chicken scratch)

We did some testing on the materials we got, and the lowest f against the cube that we tested was ~0.25 with a PTFE sheet (we also tested HDPE, LDPE, Delrin, and polycarbonate). Thus we'd need to control the clamping force from the roller to 3lbf1 or 2lbf. Not a good place to be in.

We conceptualized some other intake mechanisms using horizontal rollers and didn't like any of them. So, for now, we're pursuing a vertical roller intake design.
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Unread 01-19-2018, 04:03 PM
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Re: FRC 95 2018 Build Thread

do you have any video of your intake not working or the problem with it?
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Unread 01-20-2018, 09:08 AM
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Re: FRC 95 2018 Build Thread

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do you have any video of your intake not working or the problem with it?
We do not. Basically the cube would roll or tip instead of sliding into the intake. This could potentially be negated by using an upper roller with a long pivot arm or some other type of motion.

The issue for our purposes was that the cube wouldn't spin laterally into the intake anymore. Effectively decreasing the target area where a cube could be collected.
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Unread 01-20-2018, 09:25 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
We do not. Basically the cube would roll or tip instead of sliding into the intake. This could potentially be negated by using an upper roller with a long pivot arm or some other type of motion.

The issue for our purposes was that the cube wouldn't spin laterally into the intake anymore. Effectively decreasing the target area where a cube could be collected.

Is this basically what happened?
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Unread 01-20-2018, 09:27 AM
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Re: FRC 95 2018 Build Thread

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Is this basically what happened?
Quite comparable.

Note how their collector is pivoting waaaay back from the roller axis. This helps immensely, but will not work with our packaging scheme.
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Unread 01-20-2018, 09:32 AM
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Re: FRC 95 2018 Build Thread

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Quite comparable.

Note how their collector is pivoting waaaay back from the roller axis. This helps immensely, but will not work with our packaging scheme.
It was pivoting way back on the roller axis and it still didn't work!
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Unread 01-20-2018, 10:35 AM
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Re: FRC 95 2018 Build Thread

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It was pivoting way back on the roller axis and it still didn't work!
Not every time, no.

Reminded me of our first prototype that had a longer pivot arm. See: https://www.youtube.com/watch?v=TaUXLpf5GmM

If the arm is long enough to let the roller continue climbing up the cube it can totally work. As in: https://youtu.be/4qlRXfyLAbo?t=54s
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Unread 01-22-2018, 08:34 PM
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Re: FRC 95 2018 Build Thread

Our collector shift has us scrambling a little. We've repackaged the 'wrist' DoF from a 4-bar to a simple rotational joint lifted by an interesting arrangement of cylinders that gives us 4x total positions. Stored, deployed, and two angled positions for scoring. See below.







We're going to be prototyping some intake drive styles shortly. Our roller-based prototypes all had issues with jamming cubes that were collected at angles, as many other teams have found. We also couldn't find a timing belt that would grab the cube worth a darn. So, it's obvious we want continuous moving contact with the cube, it can be done with wheels (Triple Helix and Spectrum have some lovely prototypes they've published), but we wanted something a little different (remember that 'weirdness' column in our weighted decision matrix? yeah...) so our next prototype will feature #35 chain that has been studded with rubber bumpers.



The bumpers are ~10mm in diameter, which seems to be a good size to interlock with the structure of the milk crate inside of the bag. In fact, the green compliant wheels seem to do a great job of gripping the cubes because they squeeze into these features. We should have everything we need tomorrow. I hope to have a video within a day or two.

Our practice chassis is getting there. Hopefully driving in the next day or two!

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