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Unread 02-15-2018, 10:13 AM
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ArmaVac Range of Suction

So our intake mechanism seems to not integrate too well with our other above chassis/cube scoring mechanism nor work how we prototyped it. This was a pretty alarming discovery late last night and I'm too beyond stressed to address each point so tldr is that we're looking at other options. We have a practice bot to play with for withholding allowance but I don't want to bag the comp bot without nothing/no plan in the intakes place. I'd like at least something there.

So far we had the idea of having a piston mounted diagonally on the frame perimeter so if the cube comes in at an angle (it always pushes itself to a 45 degree angle), we have just the right amount of pressure to kick it out and drive into it. This stroke could also be used to drive into the pyramid and separate cubes. Then some passive wheels would be mounted to the sides of the perimeter opening to also guide it in as we drove into it. This seems to work decently well, but is a bit time (and pressure) consuming.

Something we noticed early in the season was the ArmaVac. We'd need to overnight ship it, so I don't want to buy it without talking to some people that have used it in the past. Basically the cut out in our perimeter for the cubes is 11" deep and 15" wide. Does anyone have videos of this working on cubes I can look at? Any general interaction videos? Any opinions on this?

Thanks.
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Unread 02-15-2018, 10:21 AM
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Re: ArmaVac Range of Suction

This particular integration took the longest time for us as well. We had several prototypes that worked well but just wouldn't package without extremely tight tolerances. What did package well in CAD didn't work well in prototyping. Do you have photos/drawings/etc you would be willing to share?

We wound up going with a gantry-style frame and side clamps since it was a reasonable compromise of both form and function.
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Unread 02-15-2018, 10:39 AM
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Re: ArmaVac Range of Suction

I worked with a team in stronghold that used a vac for picking up the boulders.

Two things we discovered.

1) You get squat for distance. You will have to hit the cube with your intake pad to stick. Even an inch out and the vac will not "draw" the cube towards it.

2) The bigger the intake pad the better. We tried different sized funnels. A 6" funnel would barely hold the boulder. A 10" funnel and students almost broke the bot when trying to pull the boulder out while the vac was on.

This was not on the vac your looking at, this was a cheapo mattress filler and we swapped the motor with a legal bag motor. You don't need a "strong" motor, just fast. You're moving air not dirt and water.


The other thing to keep in mind is that the vac is running a lot. Counter-intuitively, it is actually working harder when you don't have a game piece blocking the intake, but it is still running.
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Unread 02-15-2018, 10:51 AM
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Re: ArmaVac Range of Suction

Quote:
Originally Posted by JesseK View Post
This particular integration took the longest time for us as well. We had several prototypes that worked well but just wouldn't package without extremely tight tolerances. What did package well in CAD didn't work well in prototyping. Do you have photos/drawings/etc you would be willing to share?

We wound up going with a gantry-style frame and side clamps since it was a reasonable compromise of both form and function.
Thanks! I pm'ed you.

Quote:
Originally Posted by Fields View Post
I worked with a team in stronghold that used a vac for picking up the boulders.

Two things we discovered.

1) You get squat for distance. You will have to hit the cube with your intake pad to stick. Even an inch out and the vac will not "draw" the cube towards it.

2) The bigger the intake pad the better. We tried different sized funnels. A 6" funnel would barely hold the boulder. A 10" funnel and students almost broke the bot when trying to pull the boulder out while the vac was on.

This was not on the vac your looking at, this was a cheapo mattress filler and we swapped the motor with a legal bag motor. You don't need a "strong" motor, just fast. You're moving air not dirt and water.


The other thing to keep in mind is that the vac is running a lot. Counter-intuitively, it is actually working harder when you don't have a game piece blocking the intake, but it is still running.
This was super useful. Thank you!

I'm still open to any new suggestions. Is it reasonable to not have a solid intake before bag and tag day? I think most of the stress is coming from having so many students out with the flu (so a reduced number of people to do work/prototype/hack something) and realizing we're not going to get a chance to add something (pretty big and important) until our first competition.

My bag-and-tags up until now had pretty complete bots and this is the first year we're going without something important like a working, efficient intake. We do have a second bot to work on for the first time in our history so I don't know what to reasonably expect in terms of changing design there.
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Last edited by smitikshah : 02-15-2018 at 10:56 AM.
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Unread 02-15-2018, 11:05 AM
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Re: ArmaVac Range of Suction

Our team will likely be using a vacuum based cube manipulator and there are some things to keep in mind.

Development time, it took a part of our intake sub-team 4-5 weeks to get our system to a place where we were satisfied that it could perform significantly better than an average wheeled intake.

Diameter of your cup is important, the larger the diameter the more surface area you have to attach to.

We are not using the armavac, but we are using something similar in size. It takes 2 vacuum assemblies in series for us to get the hold on the cube that we wanted, and we are still considering adding a 3rd to the chain.

You also need to devise a release valve system so that you can release the cube quickly. Just turning the vacuum off will not release the cube instantly. Our system took ~3 seconds or so to return to normal atmospheric pressure if we only turned off the vacuum.

Power draw, and how it effects your vacuums. If your drivetrain is pulling a lot of current, your vacuum isn't going be running at full power. This can negatively effect your hold on a cube.
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Unread 02-15-2018, 11:49 AM
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Re: ArmaVac Range of Suction

We don't have a video of the ArmaVac picking up a cube, but we did a test with a suction cup that was ~9" in diameter. It picked up the cube with enough force to elevate and place on the switch / scale. One issue is changing the orientation of the cube with a suction cup that is compliant is difficult. Also, impacts from running into field elements or other robots could break the suction and cause the cube to fall. It's not a slam dunk and it may be difficult to get everything working in these last few days. If you do decide to get it, we expanded our shipping options to add one and two day type services from UPS.

I hope you figure all this out!
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Unread 02-15-2018, 12:08 PM
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Re: ArmaVac Range of Suction

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Originally Posted by JohnFogarty View Post

We are not using the armavac, but we are using something similar in size. It takes 2 vacuum assemblies in series for us to get the hold on the cube that we wanted, and we are still considering adding a 3rd to the chain.
You will find less and less return. What I would look for is what is the max vacuum a single unit can draw. Beyond this, it won't matter if you have 2 or 22 vacuums for the strength of your intake. You can only draw so much air out. More vacuums will only increase the rate of evacuating the air which helps if you have a larger volume or lots of leaks.

On cylinders, you can up the pressure and increase force until something explodes. On a vacuum, once you hit zero (or max draw of the vacuum) that's all you get.
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Unread 02-15-2018, 12:33 PM
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Re: ArmaVac Range of Suction

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Originally Posted by Fields View Post
You will find less and less return. What I would look for is what is the max vacuum a single unit can draw. Beyond this, it won't matter if you have 2 or 22 vacuums for the strength of your intake. You can only draw so much air out. More vacuums will only increase the rate of evacuating the air which helps if you have a larger volume or lots of leaks.

On cylinders, you can up the pressure and increase force until something explodes. On a vacuum, once you hit zero (or max draw of the vacuum) that's all you get.
I think you are mistaken. Flow is increased when the vacuums are in parallel.

In series, we had a two fold increase in hold via overall vacuum pressure.

I’m not an expert, but I am going off of test results.
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Unread 02-15-2018, 12:54 PM
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Re: ArmaVac Range of Suction

We are both correct here but on different items.

More vacuums will help if there are leaks which you have and are seeing with the second vacuum.

Let's say you have one vacuum that can draw down to 10 psia and a second that can draw down to 5 psia. Once in parallel the second vacuum will actually start drawing air back THROUGH the first and when maxed out will still only draw down to 5 psia.

Again the theoretical max draw would be 0 psia on a perfect leak free system. In that case, your max lifting force will be the environmental pressure ~14psi.

You can add more vacuums and it will help, but what I said is that you will get diminishing returns.
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