Chief Delphi - How did you scale?

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Re: How did you scale?

Quote:

Originally Posted by Jeremy Germita (Post 1600988)

We added a scaling mechanism for Championships. At the event, we fought some silly consistency issues that we really should have hammered out at home. The hook had a 2/10 success rate with only one of those attempts finishing in a successful scale.

After 118's reveal video came out, we began prototyping harpoon style scaling as it made the most sense for the machining resources, robot weight budget, and time available to us. I think we had a working idea of a surgical tubing powered harpoon shooter around the weekend before our first regional.

Development on a scaler slowed between Los Angeles and Las Vegas as we wanted to focus more on potential improvements to our (never fired in an official match) shooter.
After Las Vegas, we decided that scaling would give us the best chance of getting selected for alliance selections over our shooter, so we began more serious development on the scaling mechanism. We designed winch gearbox plates that were a direct drop-in replacement for our shooter motor mount plates. This allowed us to free up all of the real estate from shooting for a scaling mechanism. This was the "easy part". After calculating the proper gear ratio to lift ~140lb of robot+battery+bumpers(with some safety factor), this part of the system just worked. We used 1.9mm spectra cable as the winch line spooling onto 1/2" hex shaft. This is really good stuff for general robot use. Even when frayed and knotted, it kept on trucking. We ended up replacing the entire line when we arrived in St. Louis and again after our last qual match.

The next major component of the system was the firing mechanism. This was one of the more difficult components. We went through 8-9 iterations of this mechanism tuning different variables like barrel length, barrel dia(compared to the hook shaft dia - more on this in a bit), surgical tubing type/length/diameter/tension, and force required to lock the hook into place. We found that with this design, shot consistency increases as you increase the length of the barrel as the surgical tubing seems to have more time to send the hook flying in our desired direction. This component was built with a combination of 1x1 tubing, versaframe gussets, a few bits of 8020 brackets and two 3D printed parts(which could easily be made from delrin or some other plastics or even wood by hand). It's actually very simple. We'd probably do something similar again if we ever need a one-shot stored energy mechanism. Here's a 1/4 speed video of rev 6 firing.

The final component is the hook. This one saw ~20 iterations with variations in hook dimensions, materials, locking/closing mechanisms, and shaft length. Huge thanks has got to go out to team 842. We saw their scaling mechanism at Las Vegas and they've very graciously explained how their hook worked. Their mechanism was a HUGE inspiration for our version. This is the best picture I could find of the hook mechanism, you could also see one of the early revs of the hook in the 1/4 speed video of the firing mechanism. This is another very simple part. The "shaft" is a length of fiberglass driveway marker with a length of thunderhex shaft pressed onto the end. Early revisions of this component used Andymark churro shaft for the entire length. We moved away from this as it added a lot of unnecessary weight to the hook. This component was the most difficult component of the system. Many of the early issues was getting the hook to close on impact with the bar. Early on, we played with a bar that holds the hook open that gets pushed out of the way, allowing it to snap shut on the bar. We had difficulties with consistency and weight with this concept. After we saw 842's overcentered surgical tubing method, we knew this was the simplest and lightest concept we could implement. The version of the hooks that took the field on Galileo ended up being very similar in geometry and construction to 842's.

For this system, we developed a set of procedures to follow to ensure safe loading and transport of the robot. Without the winch line constraining the hook's flight, the stored energy in the system was enough to send the hook into our shop ceiling, piercing the ceiling tiles 1/2" deep. For robot transport, we NEVER stored the hook while energized. While in queue, we verify that the robot's air pressure is >90% (the locking/release mechanism relied on air pressure) and we don't load the hook until our robot's position was settled on the field. As far as mechanism controls goes, we have implemented a system where the operator had to hold an "enable" button before the firing button could activate the system. This prevented accidental firing on the field.
We learned from 118 and Bane in 2015 and this scaling mechanism in 2016 that stored energy systems should NOT EVER be taken lightly and teams must take utmost care in designing, handling, and operating such systems.

The scaling system was the most intensively prototyped system we've ever created. Ultimately, consistency issues bit us in the translation between the practice frame and the competition bot, but we learned so much about prototyping and which variables to watch for and tune. It was an incredible amount of fun to see this project grow from rev 1 of the firing mechanism all the way to fully scaling on Galileo Quals 60.

What kind of knot did you use to tie the Spectra to the hook?

Re: How did you scale?

Quote:

Originally Posted by Mike Marandola (Post 1601031)

What kind of knot did you use to tie the Spectra to the hook?

The knot we used is similar to the buntline hitch. The spectra was tied through a (deburred and chamfered!!)hole in the thunderhex portion of the hook shaft, shown in this picture. I don't believe there was any noticeable damage or fraying of the cable around the knot after use.

The same knot was used on the winch spooling shaft with a few turns of the spectra cable wrapped around.

Re: How did you scale?

The attached picture doesn't show much detail unfortunately, but our climber was about as simple as you could make: We had a single stage elevator we called the "ladder" with about 30" of travel (built very similar to last year's robot). the ladder, which held the hooks, used constant force springs to extend, and a strap winch to retract. At the bottom of the ladder, we installed a "push to close latch" which held the ladder once it was fully retracted.

The great things about this design were:

we didn't need to engineer any kind of custom clutch (we don't have much in the way of machining resources)
the ladder could be reset if the first attempt didn't hook (something you can't do with a ratchet)
the rigid elevator held the hooks steady when driving up the batter, something a lot of flimsier designs had trouble with.

The result was that we scaled something like 25 times in 26 attempts, something I'm very proud of.

As an aside, we really wanted to use two big 1.5" diameter, 30" travel air cylinders (and about 9 clippard tanks) instead of the winch and latch. The advantage would have been that it was mechanically simpler, and we could climb after the buzzer. Unfortunately the pneumatic version would have been about five pounds heavier than we had allowance for.

Re: How did you scale?

Quote:

Originally Posted by Mike Marandola (Post 1601031)

What kind of knot did you use to tie the Spectra to the hook?

We used Spectra as well! Can't recommend it enough. This was our knot of choice: https://www.youtube.com/watch?v=d0B6tYTVHVM . (Dyneema is another brand name that's similar to Spectra) A splice like this gets rid of the tight bends that the rope sees in a traditional knot and makes for a stronger splice. The big benefit is that it's a lot easier to deal with than a normal knot.

We also used a variation on this splice that was adjustable, so we could make a length of rope with a fixed eye splice at one end and an adjustable eye splice at the other end, giving us a rope that we could make fine adjustments to the length. We used these ropes for our climbing rope, our suspension locking mechanisms, and the hard stop for our catapult.

With all of the crazy things going on with our robot last year, the splices we made with the Spectra lines was my favorite part. If you don't have some to play with, go buy some. It's one of those things that you never knew you needed until you used it.

Re: How did you scale?

5254 had two different scaling mechanisms that made it onto our robot. During build season we prioritized climbing very low so when we finally got around to building a scaler we were left without much space to put it.

For championships we built a 118 style grappling hook. This started with a prototype that was made out of a driveway reflector. This then turned into our final hook and launcher made out of a PVC pipe and a piece of 1x1 versatubing. The hooks were spring loaded closed with surgical tubing and held open by a bar that would break away when the harpoon hits the climbing bar. This worked on our practice bot but was never successful in competition. We were having a variety of robot issues at champs so we never had enough time to get it working.

For the offseason we designed a new intake with a climber that mounted on top. This mechanism was a scissor lift that is sprung upwards with surgical tubing. When winched down the hook would detach from the velcro and tape holding the hook to the robot. Our winch was a 775 Pro in a VersaPlanetary using 2 VersaHubs and a ratcheting wrench. You can watch one of the matches where it worked here.