off-season launcher

[Bryan Herbst]

Here's what I know from 2052's launcher-

1) It has been awhile since I have seen the launcher, but I would guess it is a 3" pipe. We roll the shirts and secure the roll with a rubber band. You can roll a tshirt to just about any size. Play around with it and once you get a method that works, stick to it.

2) This will depend a lot on the individual components. The distance will also depend far more on the PSI than the amount of air you store. 2052's is a 5 gallon tank though.

3) As large as possible. 2052's are I believe 3/4", though bigger is always better in this case. You want to maximize the amount of air leaving the tank at once and you want it to exit as quickly as possible.

4) There are trade offs here. With our 5 gallon tank at about 100 PSI we could get a long shot (over the bleachers from the track on a typical HS football field), a medium shot (middle of the stands), and a short shot (just over a 3ft fence) before recharging. The biggest issue here is the compressor. The KOP compressors are NOT designed for this use. They run VERY hot, and once you get up to around 90PSI, they start cutting out and blowing the circuit breakers. We ran two KOP compressors and still had some troubles. If you can, get a bigger compressor.

As for your last question- we run ours on the track, though I would be wary on the field. Maybe someone else can chime in on that bit.

[Mk.32]

The KOP compressor is ONLY rated for a 1 gallon tank. We used a 1 gal tank on the robot and the compressor was pushed very hard, though had no problems.
I would definitely get something more powerful.
I have drive the kOP 6 wheel robot over a grass field and it worked fine, though muddy might make it more difficult.

[Da Kid]

Tanis, by the way you answered the questions it seems you have a different set up than we plan.

this is what we are planning to do:
Main tank(120 psi)-->pressure regulators-->A secondary tank for each of the three barrels(different psi's)-->Sprinkler valve-->actual barrels.

and we haven't bought anything yet so i am actually asking what would be a good size for the main and secondary tanks for three barrels (there will be plenty of time to recharge after each set of three shots). what has worked for other teams in the past?

and one more question. if the whole system is pre-loaded with an actual compressor to 120 psi and the kop one is just used to top it off is that still too much for the kop compressor?

[NickE]

Instead of a sprinkler valve, you might be better off with something pressure rated for compressed gases. Sprinkler valves are designed for liquid and if a failure arises, it would likely be catastrophic. For a robot that's going to promote your team in front of people, it's probably better to be safe than sorry.

We're running 6 6" KOP "sticky" wheels on our t-shirt cannon with the center wheel dropped. They work fine on a variety of surfaces.

[IanW]

While it is certainly better to use components that are rated for air pressure, I found in my own (not too extensive) research that large enough solenoid valves (1" diameter) would be prohibitively expensive for some teams. However, if you know of some source that has such valves for cheap, I would definitely look into it.

And before someone says that an catastrophic failure would also be "prohibitively expensive," I guess that's just something teams will have to consider. I suppose the other option is to just wrap the sprinkler valve in layers (and layers (and layers)) of duct tape.

If you're looking to build a t-shirt launcher, then why do what everybody else is doing and make a pneumatic canon? Our team decided to try a different strategy, that was both cost effective, crowd-pleasing, and a far shooter! Say hello to the t-shirt SLINGSHOT! Just get some surgical tubing, a long robot, and....BAM! A self-firing, enjoyable, and can shoot more than t-shirts robot! We made ours out of things we found in our robotics room.

Below is the original version (we've been working on it)!

[Da Kid]

i agree that a catastrophic explosion would be bad but we plan to put the three barrels inside of a large diameter piece of PVC so even if something does explode it will be contained.

again if someone could chime in on tank sizes(main and secondary) that would be very helpful.

and after looking around i found most of the valves are 24 volt ones. our team isn't the richest(we hope more people will sponsor us one they see this robot) is there a place to get cheap 12 to 24 volt converters. i've looked around and it seems most are around $50 that i've seen.

[114Klutz]

Originally Posted by Da Kid

i agree that a catastrophic explosion would be bad but we plan to put the three barrels inside of a large diameter piece of PVC so even if something does explode it will be contained.

again if someone could chime in on tank sizes(main and secondary) that would be very helpful.

and after looking around i found most of the valves are 24 volt ones. our team isn't the richest(we hope more people will sponsor us one they see this robot) is there a place to get cheap 12 to 24 volt converters. i've looked around and it seems most are around $50 that i've seen.

This is an off season project - why not just run 2 batteries in series? The minibot batteries are 12v each.

[OSU_Springer]

Originally Posted by 114Klutz

This is an off season project - why not just run 2 batteries in series? The minibot batteries are 12v each.

Excellent idea. I would caution that care must be taken here to not then wire the subsequent 24 VDC potential into the PD board. I'm sure that the transformer(s) there would not like the new voltage, nor would the downstream components.

To be safe, I would search places like allied electronics and newark for a 2-turn transformer. This would give you your voltage conversion from 12 VDC to 24 VDC. Just make sure that the transformer is rated for the right power (watts) or amperage, depending on how the spec is written.

[Da Kid]

Originally Posted by 114Klutz

This is an off season project - why not just run 2 batteries in series? The minibot batteries are 12v each.

i've searched around and found out that an AC sprinkler valve on a DC circuit can be run on lower voltage since DC isn't as affected by either a resistance or an inductor and thus has more current. 12 volts should be fine.

[NickE]

Originally Posted by Team2374

While it is certainly better to use components that are rated for air pressure, I found in my own (not too extensive) research that large enough solenoid valves (1" diameter) would be prohibitively expensive for some teams. However, if you know of some source that has such valves for cheap, I would definitely look into it.

And before someone says that an catastrophic failure would also be "prohibitively expensive," I guess that's just something teams will have to consider. I suppose the other option is to just wrap the sprinkler valve in layers (and layers (and layers)) of duct tape.

A catastrophic failure would be more than expensive. It has the potential to seriously injure team members or spectators regardless of how much duct tape you wrap around it. Is that really a risk you, your team and your school are willing to take to save a few bucks?

[IanW]

Hence why I put "prohibitively expensive" in quotes the second time.
I would still like to know what valve 254 uses - might make my entire point moot.

[NickE]

Originally Posted by Team2374

Hence why I put "prohibitively expensive" in quotes the second time.
I would still like to know what valve 254 uses - might make my entire point moot.

From our team website:
1" NPT MAC Solenoid Valve at ~17.0 cV Flow Capacity with a 23 ms Response Time.

For the increased reliability, safety, performance and peace of mind, buying a quality valve was well worth the investment.

[OSU_Springer]

Originally Posted by NickE

From our team website:
1" NPT MAC Solenoid Valve at ~17.0 cV Flow Capacity with a 23 ms Response Time.

For the increased reliability, safety, performance and peace of mind, buying a quality valve was well worth the investment.

An ASCO 8210G004 12 VDC solenoid valve is $218 LIST. You can probably get this cheaper if you go to a distributor and explain that you are a school related team. This is a 1" NPT valve, with a full bore orifice. If you step up to the 1 1/2" NPT 8210G022 12VDC solenoid valve, you get a much higher Cv (22.5 vs 13) but your price goes up to $405.

Both of these valves are only rated for 125 PSIG, so be careful not to try climbing above that. The biggest thing with building the air cannon is making sure that you can get an appropriate amount of air into the barrel in as short amount of time as possible. That's why it seems that higher pressures are better. You'll only need a limited amount of pressure if you can get the flow high enough. This of course also depends on your secondary accumulator (tank) volume. Make it too small and you won't have enough air to accelerate the projectile to a proper velocity, make it too large and you are just wasting energy (assuming equal barrel lengths).

A note on compressor usage: Do not expect kit compressors to last very long if you are using them constantly. They are surely not rated for anything higher than a 10-15% duty cycle. This means that they are only rated to run at the pressure rating for 10-15% of time. In other words, 6-9 minutes out of every hour. Running them more than that risks overheating the compressor and burning something out.

[Bryan Herbst]

Originally Posted by NickE

A catastrophic failure would be more than expensive. It has the potential to seriously injure team members or spectators regardless of how much duct tape you wrap around it. Is that really a risk you, your team and your school are willing to take to save a few bucks?

Out of curiosity, have you ever heard of an incident involving a sprinkler valve failure?

There are plenty of stories about and warnings against using PVC to store air, but I have never before heard someone claim that using a sprinkler valve would be dangerous.

Sprinkler valves are typically very solid. I wish I had a data sheet on hand for one of them. If someone does, could you read off the ratings?