Using a Solenoid in a Pneumatic Cannon

[wiiking123]

Our team was thinking of making a T-Shirt launcher as something to do during off-season. Can a solenoid open and close fast enough to keep decent amount of air pressure left in an air reservoir? We will be using the solenoid provided in the 2011 KoP. Also, if you have made a T-Shirt cannon in the past, how much air should we keep reserved?

[PAR_WIG1350]

typically the idea is actually dump ALL of the air out as quickly as possible. The system generally has a separate firing reservoir that is filled from the compressor and additional accumulators before being isolated from that portion of the system. Then, ALL air from the firing reservoir is dumped into the barrel to launch the t-shirt out. I don't recommend the KOP solenoids due to the fact air passes through them relatively slowly. Sprinkler valves are used often for these applications.

[wiiking123]

Also, would the tubing that comes with the standard KoP be able to release the air from all the reservoir tanks fast enough?

[Mr V]

No the kop stuff won't cut it we use 4 3/4" automotive air suspension valves we got from airbagit.com, for hose we use 1/2" air brake hose. For the tank we have 1.5 gal with multiple outlets. The compressor we use is the big brother of this year kop unit that is rated for 200 psi and a 100% duty cycle. We run at ~180 psi with a quick finger you can leave~ 150 psi in the tank and shoot the shirt ~100ft letting it go a little longer leaving 100 psi in the tank and shooting the shirt~ 200 ft. We have come to the conclusion that it is not the pressure that send the shirt flying it is the air jets. Web ad bought some expensive fiesto 1/2" valves and they were to slow. The air suspension valves are "designed" to launch a 3500+ lb car in the air so they are fast.

[NickE]

On our t-shirt cannon, we are using a 1" NPT MAC Solenoid Valve at ~17.0 cV Flow Capacity with a 23 ms Response Time. The valve is connected to the barrel with a 1" NPT steel-braided hose. The high flow rate and reponse time is really what makes the cannon work great. We are actually able to vary the amount of time we open the valve from ~25ms to ~80ms to change the distance the shirt is launched. http://team254.com/media/photos/imag...pe=img&id=4589

We store our air in a large scuba tank at ~3000 psi. This air is regulated down into a secondary scuba tank which holds air at about 150psi, our shooting pressure. Once pressurized at a dive shop, we can get more than 200 shots before the high-pressure tank needs refilling.

[rahilm]

Originally Posted by wiiking123

Also, would the tubing that comes with the standard KoP be able to release the air from all the reservoir tanks fast enough?

Won't really come close (I know these calculations are for incompressible fluids generally, but for these purposes, they will work):

If we assume 120psi (827370.84 Pa)
pressure = (.5)(density)(velocity)^2
velocity = sqrt((pressure)/((0.5)(density)))
velocity = sqrt((827370.84)/((0.5)(1.225)))
velocity = 1162 m/s

With the tube being used, we only have a 1/8" diameter, which is 0.003175m
air flow = area * velocity
air flow = (diameter/2)^2 * velocity
air flow = 0.003 m^3/s

mass flow = 0.0036 kg/s

Basically, you're going to have 3.6g of air coming out every second, which is not even close to enough to move a t-shirt (and this is assuming 100% efficiency)

If you are working on a low budget, but have a robot chassis lying around, message me and I could put together a bill of materials on our t-shirt shooter. (Cost about $250 all parts from Home Depot)

[Mr V]

Originally Posted by rahilm

If you are working on a low budget, but have a robot chassis lying around, message me and I could put together a bill of materials on our t-shirt shooter. (Cost about $250 all parts from Home Depot)

I strongly recommend against using parts from HD for your pneumatics sprinter valves aren't rated for the pressure or vibration of a vehicle. The valves we are using are rated for 300 psi are only~ $30 ea and are rebuildable.

[wiiking123]

Originally Posted by rahilm

Won't really come close (I know these calculations are for incompressible fluids generally, but for these purposes, they will work):

If we assume 120psi (827370.84 Pa)
pressure = (.5)(density)(velocity)^2
velocity = sqrt((pressure)/((0.5)(density)))
velocity = sqrt((827370.84)/((0.5)(1.225)))
velocity = 1162 m/s

With the tube being used, we only have a 1/8" diameter, which is 0.003175m
air flow = area * velocity
air flow = (diameter/2)^2 * velocity
air flow = 0.003 m^3/s

mass flow = 0.0036 kg/s

Basically, you're going to have 3.6g of air coming out every second, which is not even close to enough to move a t-shirt (and this is assuming 100% efficiency)

If you are working on a low budget, but have a robot chassis lying around, message me and I could put together a bill of materials on our t-shirt shooter. (Cost about $250 all parts from Home Depot)

A BoM would be greatly appreciated if you could put it together. Since we are a rookie team, we really are going into pneumatics for the first time. One of our mentors knows some, but any tips would be greatly appreciated.

[Phyrxes]

Please make sure that anything that is holding pressurized air is rated for it! Also if your team is located at a school or wishes to use the T-shirt cannon at school events check with the administration/central office/whoever to make sure its its LEGAL for you to have/operate a T-shirt cannon on school grounds or at school events.

Background: Up until recently Virginia classified any "pneumatic projectile device" as a firearm (so paintball guns, airsoft, t-shirt cannons, etc) which could cause some serious issues with law enforcement and/or administrators. They have since clarified that law, thanks ROTC!, so that they are permissible as part of an official school function and their "operation" is directly supervised by a staff member.

So please check, and be safe! Our school district was very receptive to the idea when we submitted a design review that showed that ours conformed to all OSHA standards for pressurized air, plus its something neat to show off.

[Mr V]

Originally Posted by wiiking123

A BoM would be greatly appreciated if you could put it together. Since we are a rookie team, we really are going into pneumatics for the first time. One of our mentors knows some, but any tips would be greatly appreciated.

When we get back home from th Oregon regional I can put you together a safe bom that uses components rated for air at the pressure needed to shoot t shirts a good distance w/o breaking the bank.