1726 Prototype Testing

[TheOtherGuy]

Here's a short video of our prototype mechanisms in use.

http://www.youtube.com/watch?v=LDvo2uY7dcU

You can also see some picture going up at:

http://photos.project1726.org

Comments, questions, suggestions appreciated!

[DarkFlame145]

very nice, it goes up really high

[TheOtherGuy]

It goes a little higher when you hold it down (like it will once the last component is finished)

http://www.youtube.com/watch?v=G9y-LhHRAHw

[neoshaakti]

oh man that catapult is BEAST
what did you use to power the catapult?

I cant really tell, but is ure robot within the 28 by 38 requirement ?

[DonRotolo]

Best one I have see so far! That's great!

[TheOtherGuy]

oh man that catapult is BEAST
what did you use to power the catapult?

I cant really tell, but is ure robot within the 28 by 38 requirement ?

I wasn't working on that component, but I think we have 2 2" bore 10" stroke pneumatic pistons. We did a 'trick' (well known, I think) by keeping the cylinder from moving at 60psi with 3in. filled. Then we release the ball, and the air stored in the 1/3rd of the cylinder expands very quickly, giving us enough force to launch the ball.

Right now we're working on lowering the air consumption (right now a single shot drops our pressure from 115psi to about 80psi...)

And yes, I believe it is within the limits... However, this is a culmination of 2 prototypes, a mechanism mounting bracket, and last year's robot. The real thing will (hopefully) be much nicer

[neoshaakti]

We did a 'trick' (well known, I think) by keeping the cylinder from moving at 60psi with 3in. filled. Then we release the ball, and the air stored in the 1/3rd of the cylinder expands very quickly, giving us enough force to launch the ball.


what do you mean by keeping the cylinder from moving at 60 psi with 3 in filled?

sorry Im a nub

[TheOtherGuy]

basically when the catapult is fully retracted, the cylinder sticks out 3 in. Before we shoot, we hold down the ball (from the top, we still have to make that part) and open the valve. Air from the tanks fills up that 3in. and we wait until it is time to fire. When we fire, we remove the top piece and the air inside the cylinders expands rapidly, launching the ball.

Maybe I should make a quick diagram...

[neoshaakti]

basically when the catapult is fully retracted, the cylinder sticks out 3 in. Before we shoot, we hold down the ball (from the top, we still have to make that part) and open the valve. Air from the tanks fills up that 3in. and we wait until it is time to fire. When we fire, we remove the top piece and the air inside the cylinders expands rapidly, launching the ball.

Maybe I should make a quick diagram...

so your bore starts 3 inches, and it fires out to 10? so basically you're using the potential energy of the bore that is protruding 3 inches?
yeah a diagram might help...

[MrJebus]

Think of it like a spring, but instead of energy being stored in the coils, its stored in the cylinder with the air. Only reason that it sticks out 3in is so the pressure can build, storing the energy.

[TheOtherGuy]

so your bore starts 3 inches, and it fires out to 10? so basically you're using the potential energy of the bore that is protruding 3 inches?
yeah a diagram might help...
Exactly!

Here's a diagram (out of proportion and not quite right, but what the hay):
http://img341.imageshack.us/img341/292/catapultse9.th.png (http://img341.imageshack.us/my.php?image=catapultse9.png)

[neoshaakti]

Exactly!

Here's a diagram (out of proportion and not quite right, but what the hay):
http://img341.imageshack.us/img341/292/catapultse9.th.png (http://img341.imageshack.us/my.php?image=catapultse9.png)

Oh that is pretty cool
do u have to program the bore to protrude 3 " out, or do u mechanically set block it from full retracting (Im guessing the 2nd...programming a bore doesnt seem probable)
haha

[=Martin=Taylor=]

Are you at all worried about running out of air?

I think you might hurdle too fast (:D ) and drain your tanks.

[TheOtherGuy]

actually, yes, we are very worried about running out of air! Right now we lose about 35-40psi per shot, and it takes ~25-30 seconds to reload... Of course, you don't have to shoot it at 115psi, but we still plan on exploring different ways to conserve air.

[=Martin=Taylor=]

Well, you could start by removing all the other pistons.

Use servos to shift, and a motor to lift the loading forks. Pressurizing your tanks before every match might help maximize your air.

[Matt H.]

We hold the cylinders at 3in by using the weight of the ball combined with the piece (not yet built) which holds down the ball. Because of the geometry of the catapult it takes very little force to hold it down, but increases exponentially when released.

We are trying to cut down air usage and have been somewhat successful. Almost all of our cylinders are now single action instead of double action. By doing this we have cut air consumption for one shot from about 115-70 to 115-90 psi drop on four tanks (about 15 sec recharge time). If we start with the tanks precharged we should be able to get through a match without too much trouble.

On a side note does anyone know if it's possible to design a pressure readout display for the OI. I think that would be immensely helpful this year.

[s_forbes]

Well, you could start by removing all the other pistons.

Use servos to shift, and a motor to lift the loading forks. Pressurizing your tanks before every match might help maximize your air.

Shift? what shift?

From what I understand they didn't optimize the shooting system at all; it really only needs to fill the initial 3", not all 10". That should save a ton of air for the other tasks.

[TheOtherGuy]

we also accidentally managed to land the trackball on the overpass:

http://www.youtube.com/watch?v=X3oHbSovZjA

it's actually pretty easy with a catapult!

[Sunshine]

Awesome Job.

very impressive !

[Gdeaver]

These guys have been concerned with the safety issue of stored energy. Their design makes every attempt to minimize the risk of injury. Most notable they do not use a latching mechanism. If I was an inspector, I would probable let this go. Some of the other designs I've seen are too risky and If I were the inspector would not allow to compete. I'm pessimistic. Who Knows what the inspectors will say. The GDC has not been black and white on this. A ball can be launch with a minimal risk device. Come on teams keep thinking. It can be done.

[falconmaster]

Oh that is pretty cool
do u have to program the bore to protrude 3 " out, or do u mechanically set block it from full retracting (Im guessing the 2nd...programming a bore doesnt seem probable)
haha

You guys are awesome! Great Job! Great idea!!!

[jhaugen]

That's outrageous. Looks great.

[dtengineering]

On a side note does anyone know if it's possible to design a pressure readout display for the OI. I think that would be immensely helpful this year.

First of all... wow. We spent the first couple weeks planning to lift, until we got fed up with the 80" cylinder, then said "what the heck" and started putting together launch prototypes last week. We managed to get the ball onto the overpass using two 1.5 x 8" cylinders... but without any preload. The only catch was that we used the 120psi feed from the shop compressor, so it was back to the drawing board. This weekend involved sitting around with the calculator, spreadsheet, and a demo copy of Working Model to calculate what we'd need to do it with 1.5x8" cylinders as... for some reason... we have five of them kicking around the shop. Lo and behold, the calculations came out very close to your observations. Thanks!

Now, perhaps, I can return the favour, by suggesting that the device you are looking for is called a "pressure transducer" and that a quick search of the forums here brings up a link to here (http://www.pneumaticsfirst.org/2006Game/Components.htm)where you can see a picture of one that was apparently in the 2006 KOP. It's possible you have one sitting in your shop and don't know of it!

As for sending the data back and displaying it, I suspect your programming team is on top of how to send it, and perhaps someone is building a custom dashboard in labview?

Thanks again... I feel so much more confident with our design knowing that our calculations are not entirely off-base!

Jason

[MrForbes]

Thanks for the tip Jason, but I looked thru the 2006 KOP checklist and I do not see that transducer listed. I sure don't recall ever seeing it in my many diggings thru the pneumatic parts bin either. Maybe it is just something that was used the year before, and not in 2006, and got left in the manual? notice the page on your link shows that it's from 2005 and then relabeled 2006 at the very top

[dtengineering]

Thanks for the tip Jason, but I looked thru the 2006 KOP checklist and I do not see that transducer listed. I sure don't recall ever seeing it in my many diggings thru the pneumatic parts bin either. Maybe it is just something that was used the year before, and not in 2006, and got left in the manual? notice the page on your link shows that it's from 2005 and then relabeled 2006 at the very top

Hi Jim! I thought I'd seen that launcher design before... I never clued in to this being your team:confused: ! Great job.

You've got me looking around for the a place that sells the pressure transducer now, as I'm pretty sure we've got one in the shop, but if it isn't COTS any more, then I guess that is where it is going to be staying. A bit of a pain, as they seem to run about $100 or so, but here's one that I found at digikey that might do the trick.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=MSP3251P1-ND

Note that I've never actually used the transducer before, so I can't say for sure that this is exactly what you need... I just remember one being in the KOP some years ago and having it sit around on the shelf and thinking hmmm.... we've got to use that one of these years.

Jason

[Matt H.]

Thank you very much for the help Jason. There has been a lively discussion of this on our team forum and the other option which has been considered is the use of several pressure switches to provide a general idea of where the pressure is (one at 20psi, one at 60psi etc.). Either way it's an interesting problem. Do you plan on using all five of your 1.5*8" cylinders?

[dtengineering]

No, no... thank YOU! We had the calculations all done to SAY it would work, and we had some preliminary test data that matched our calculations... but given my marks in thermo and fluids 20 years ago in university, there was... well... probably close to a 50% chance we were wrong (hopefully I've got better since)! As you have been kind enough to share your results, when I compare your observations to what my model predicts (and the demo version of working model won't let me save.. fair enough... or I'd post it here) it validates the model. We will be building this week with far more confidence!

As for the transducers, some digging around on the web shows that T.I. Instruments is now www.sensata.com Unfortunately they don't show a 5cp3-7 sensor in their product line, but I've dropped them an e-mail to ask if there is a derived or evolved version of it, or perhaps they just changed the part number, which should make it a legal COTS item. I will try to remember to report back here if I find anything useful.

Jason

EDIT: The plan is to design for five of the cylinders, then cut back if we can, either by dialling the regulator back, or dropping one cylinder. The idea behind using more of the smaller cylinders (besides the fact that we've got them...) is that gives us five "tubes" of airflow to keep the pressure up throughout the stroke, while with a larger diameter cylinder we would only have two, or perhaps three. Not that this appears to be a problem. We are also considering setting up the system as Two clippards --- Regulator ---- Valve ----- Two Clippards ---- Cylinders so that there is no bottle neck due to the valve. This will hopefully reduce the amount of pre-load we need, and allowing us to maximize the useful stroke of the 8" cylinders.

[MrForbes]

I think you have to have all the air storage (clippard) tanks before the main regulator or any valves...might want to carefully read the rules before trying it any other way....

[pakratt1991]

the pressure sensor that FIRST supplies is not able to give a read-out, you'll need to add some other sort of sensor and add some to display the number on the robot controller side (laptop with some sort of interface will work.)
:yikes: great job

[Gdeaver]

You can have the air storage tanks after the main regulator. This may help with the pressure drop and reaction time of the main regulator. There are cheaper pressure transducers but the cheap one are 5-20 ma or raw sensors. For 0-5 volt your going to spend some money.

[team2061]

kinda looks like what where going with. great job.

[Frank Neuperger]

Nice job. It appears that the ball develops a rearward spin with this design as it rolls off the catapult forks. This is elegant. It seemed to roll back towards the bot after the shot.

The mechanism illustration suggests an "over center" latching scheme where actuators initially pressurize with the force vector of the actuators aimed just below center of the mechnism fulcrum. As such it will not fire unless somthing bumps them above the fulcrum. Possibly the small gizmo at the far left of the illustration does this. Getting both actuators "over center" at the same time may be a challenge due to build tolerances and mechanism flex.

I wonder about the shot to shot repeatability in terms of height and trajectory. To be shooting on the move, the shot to shot repeatability would be important.

[team2061]

What makes the "ball pick up" device go foward and back

[TheOtherGuy]

Nice job. It appears that the ball develops a rearward spin with this design as it rolls off the catapult forks. This is elegant. It seemed to roll back towards the bot after the shot.

The mechanism illustration suggests an "over center" latching scheme where actuators initially pressurize with the force vector of the actuators aimed just below center of the mechnism fulcrum. As such it will not fire unless somthing bumps them above the fulcrum. Possibly the small gizmo at the far left of the illustration does this. Getting both actuators "over center" at the same time may be a challenge due to build tolerances and mechanism flex.

I wonder about the shot to shot repeatability in terms of height and trajectory. To be shooting on the move, the shot to shot repeatability would be important.

Actually, I'm just really bad at making drawings :) I believe this picture from our gallery demonstrates it best:
http://photos.project1726.org/albums/userpics/10011/normal_DSCN1731.JPG (http://photos.project1726.org/albums/userpics/10011/DSCN1731.JPG)
the point where the piston attaches is just above the line created by the front pivot point and the end of the flinging arm. When the cylinders are pressurized, the catapult "slowly" begins moving because of that slight height. The end pieces you see are just mechanical stops so the catapult arms are always under the point where the piston attaches.

As for the ball-picker-upper, we simply use a pneumatic piston right now, but may end up switching to a motor to conserve air for the catapult:
http://photos.project1726.org/albums/userpics/10011/normal_DSCN1720.JPG (http://photos.project1726.org/albums/userpics/10011/DSCN1720.JPG)

[Frank Neuperger]

Thanks of the clarification and the details. Your design is a real inspiration to others that are looking at catapults.

How is shot to shot repeatability in terms of height and trajectory?

Regards
Frank

[MrForbes]

We won't know how repeatable it is until we build the last part, which is an arm that sits on top of the ball to hold it down, and is raised when we want to fire the ball. The idea is to use the downward force of this arm plus the weight of the ball to overcome the initial vertical upward force of the catapult...and then when the top arm is released, the vertical force of the catpult is greater than the weight of the ball, so the ball fires. In our initial tests using my arm as the ball holder downer, this seems to work ok, but we need to do some fabrication soon (ie today) to get that arm built and on the robot, so we can answer your question more accurately :)

[x7shaddow]

you're loader mechanism seems to work well but I'd hate to see what happens when you accidentally run into a wall at full speed

[MrForbes]

heh...we already know what happens when we do that! and so we're working on other ways to build it to take more abuse.

[TheOtherGuy]

you're loader mechanism seems to work well but I'd hate to see what happens when you accidentally run into a wall at full speed

Funny you should mention that! We were working on a design today for a collapsible ball picker-upper:
http://img295.imageshack.us/img295/7307/dscn1819uy1.th.jpg (http://img295.imageshack.us/my.php?image=dscn1819uy1.jpg)

The 1/4" strip of lexan acts as a slight spring. It takes just the right amount of force to push it, and the aluminum bracket prevents the arm from swinging out.

We realized we need to design this after we (I) accidentally test-crashed the manipulator into a wall and it was almost mangled beyond repair (but not quite, because we did repair it)

[falconmaster]

Here is our version of your catapult!http://www.youtube.com/watch?v=LwmyQMlmaRY
Thanks for the help!

[MrForbes]

Nice! see, it's not so hard to do :)

[dtengineering]

Different configurations are likely to work, too. We've prototyped one arm of our two armed launcher and achieved heights of about 5' at a 45 degree angle using just two 1.5x8" cylinders and one clippard tank of air at 60 psi. We are building the second arm (two more cylinders, one more tank) and expecting to clear about 8' with both working together. We'll post some video when we get that happening.

As for picking up the ball... just try smashing it into the wall. If your front end is low the ball shoots up, and you drive right underneath it as it falls back down.

Not particularly elegant, and not much good in the open field, but I'm not quite sure how anyone is going to get a ball to sit still on the open field for them to grab anyways. Mind you, I may be wrong about that... I haven't played this game before, you see...

Jason

[TheOtherGuy]

actually, we have an automated system for picking up the ball that appears to work quite nicely ;) All we have to do is run into it...

[Frank Neuperger]

Was there any validity to the following comment that was posted on the YouTube video at
http://www.youtube.com/watch?v=G9y-LhHRAHw&feature=related

=================
dougji I hate to burst your guys bubble, but this is illegal. You're not allowed any "sudden stop" launching mechanisms.

frc1726 (2 days ago) Could you please cite a rule, Q&A response, or team update paragraph that says that? We haven't seen any such thing, and would like to know if you are correct. =================

What is the definition of a "sudden stop" launching mechanism?

Regards
Frank

[MrForbes]

I have not found anything that gives it any validity, and I think the person who posted that might not understand how our robot works.

[dtengineering]

Was there any validity to the following comment that was posted on the YouTube video at
http://www.youtube.com/watch?v=G9y-LhHRAHw&feature=related

=================
dougji I hate to burst your guys bubble, but this is illegal. You're not allowed any "sudden stop" launching mechanisms.

frc1726 (2 days ago) Could you please cite a rule, Q&A response, or team update paragraph that says that? We haven't seen any such thing, and would like to know if you are correct. =================

What is the definition of a "sudden stop" launching mechanism?

Regards
Frank

Not only does the comment on youtube represent an incomplete understanding of the very clever system that 1726 has devised, but also an incomplete understanding of the Q&A. It has been specifically answered that building up pressure in a pneumatic cylinder, then releasing it is perfectly legal given that certain other conditions are met.

There is an excellent discussion of this topic here http://www.chiefdelphi.com/forums/showthread.php?threadid=62836 with links to relevant Q&A answers/clarifications.

In short... launch away my friends... just not in the pits and not using any system of compression other than the compressor, or any pressures exceeding 60 psi on the working side of the system.

Jason

[hipsterjr]

Quick Question:

Are you guys recycling the air from the launcher cyclinders' exhaust or just letting it vent?

If so, how? We are also a little worried about and air consumption.

[s_forbes]

Quick Question:

Are you guys recycling the air from the launcher cyclinders' exhaust or just letting it vent?

If so, how? We are also a little worried about and air consumption.

I'm pretty certain there is no way you are going to be able to 'recycle' air that has been used to do work and still get something useful out of it. (I think it's a violation of one of those important Thermodynamics laws)

I think the other ends of the cylinders are just vented to the atmosphere. The team is working on a way to make the system only need air in the one direction by having the cylinders return automatically when the air pressure is cut.

Also, the timing of the actuation is important. We really only get work out out of the first 3" of compressed air in the cylinder, so it doesn't make sense to keep spilling the air into cylinder after it's allowed to fire. The most efficient way to do it would be to fill the cylinders, and then close the valve immediately after letting the arms go (so as not to break the 'open valve' restriction) These savings all add up, and the system I just described would use about 1/10 of the total air that a double acting, full out pressure set up would (with our two 10" stroke cylinders, at least).

It's kind of hard to explain in a post, but hopefully you get the idea...

[team2061]

Can you guys do me a favor and post some side pictures with the ball in the "ready to launch mode"

[s_forbes]

I've been trying to get them to post more pictures for days now (I'm up at college right now and I don't get to play robots :(), but they keep making excuses like they have to do homework and stuff...

They should be home any minute now, maybe one of them could put up more pics.

[MrForbes]

yeah, lots of excuses! we actually got the "rake" thing on the top of the robot that retains the ball before shooting, done tonight! but it was time to go home just as the pneumatic plumbing was completed, so no "real" shooting tests got done.

But we did get the robot to catch the ball after knocking it off the overpass...on the second try...it's pretty easy to do.

film at eleven....

[TheOtherGuy]

I've been trying to get them to post more pictures for days now (I'm up at college right now and I don't get to play robots :(), but they keep making excuses like they have to do homework and stuff...

They should be home any minute now, maybe one of them could put up more pics.

Unfortunately that won't be happening... our hosting service's server crashed and they are spending a lot of time fixing it. While they're working on it, the server is in read-only mode and files cannot be uploaded, so no pictures or forum until the server is fixed!

.

[hipsterjr]

I'm pretty certain there is no way you are going to be able to 'recycle' air that has been used to do work and still get something useful out of it. (I think it's a violation of one of those important Thermodynamics laws)

I think the other ends of the cylinders are just vented to the atmosphere. The team is working on a way to make the system only need air in the one direction by having the cylinders return automatically when the air pressure is cut.

Also, the timing of the actuation is important. We really only get work out out of the first 3" of compressed air in the cylinder, so it doesn't make sense to keep spilling the air into cylinder after it's allowed to fire. The most efficient way to do it would be to fill the cylinders, and then close the valve immediately after letting the arms go (so as not to break the 'open valve' restriction) These savings all add up, and the system I just described would use about 1/10 of the total air that a double acting, full out pressure set up would (with our two 10" stroke cylinders, at least).

It's kind of hard to explain in a post, but hopefully you get the idea...


Thanks, just curious because I saw that you had the exhast port with tubing coming out of it and was woundering if it ran to anything. Your plan for the phumatics sounds very ingenious, nice work:D !

[otomerobot]

Oh man, that this is beastly! :yikes:
Someone alrady probably asked this, but how much psi are you using on that?

[Matt H.]

In a four tank configuration our psi drops by about 30 per shot. We are doing our best to conserve air and hopefully will be able to get through the matches especially if we start with the tanks precharged.