# Pneumatics Help

Can you wire a single solenoid and a double solenoid to the same relay?

Wiring two solenoids to one relay is legal. Whether it’s a good idea to have different types of solenoids on the same relay, I don’t know.

Is it possible?

well anything is possible. but i dont see why you would want to run them together. can you explain what youre trying to do are you trying to operate two functions at once

I have another pneumatics question (sorry if it’s off-topic)

How many pistons could you feasibly put on a robot. Our team is thinking of two 2" pistons, and three other 1/2" ones. How much is this going to tax our compressor?

Has any other team used a similar number of pistons? What type of performance did you get?

Thanks,
Sam

oh how i love pneumatics. well the 2 inch obviously is going to take out most or your air. and then on these it depends on if they are single acting cylinders or just the standard dual action.

I don’t think 1/2" cylinders are legal… Anyway, you can’t get an air usage estimate without specifying stroke length as well. A 2" diameter with 6" stroke will take about the same amount of air (a few cu in difference) as a 1.5" cylinder with a 12" stroke*, for example.

*Yes, I know 1.5" bore cylinders with 12" stroke lengths aren’t legal; I chose that number for example purposes only.

Although I remember that there are some horrible entropy and enthalphy type calculations that I really didn’t get in third year thermo, and have even less appreciation for now, the main rule governing how much air is consumed is your good old high-school p1v1=p2v2 ideal gas law. (And, yeah, I left out the t1 and t2 divisors since it isn’t too unfair to assume everything stays about the same temperature…)

So what this means is that when you compress a clippard tank (6" x 2" dia = 6 pi cubic inches) to 120 psi, you have (120psi * 6 pi cubic inches) = 720 pi pound inches of air.

When you use that air to fill a 1.5" x 8" stroke cylinder (4.5 pi cubic inches)with 60 psi of air, you will “use” (60 psi x 4.5 pi cubic inches) = 270 pi pound inches of air.

Remember that this will also cause a pressure drop in the clippard tank. In this case the pressure in the tank will drop to 720 pi - 270 pi = 450 pi pound inches, which will occupy a volume of 6 pi cubic inches, with a resulting pressure of 450/6 = 75 psi.

So consider that one clippard cylinder can pressurize a 2" x 6" cylinder to 60 psi before the pressure in the cylinder drops below 60 psi. (Not that there is anything wrong with that… it just means that if you make a second stroke before the compressor re-charges the clippard cylinder that the second stroke will be at lower pressure and thus reduced force.)

It would take the compressor several seconds (probably less than ten, though) to recharge the clippard cylinder back to roughly 120 psi, although this depends on battery charge and other current draws to the electrical system. So really, it isn’t a question of how many cylinders you put on the robot… but rather how big they are and how often you “fire” them.

Jason

Jason’s equations should be used to check to see how much you will need your pump and if you need 1, 2, 3, or 4 accumulators (clippard tanks).

Now back to the original question. The double solenoid actually has two active solenoid coils (thus the word “double” in the name). What this means is that in order to make it work properly you need two commands: open and closed. A single relay can be used with one double solenoid if you add diodes to each leg of the relay. I have attached a picture from the 2005 guidelines document as I could not find it in any of the current documentation.

Now, you can connect a single solenoid and a double solenoid to the same relay, but why? The single solenoid will actuate when one of the double solenoids actuates so why not just conect a “T” fitting to one leg of the double solenoid to actuate your second device? We will be using this method this year on our shifters.

-Paul

And hey… I just stumbled upon this presentation.

http://first.wpi.edu/2007CON_Pneumatic_Power_Olivera.pdf

Very interesting stuff, including some research suggesting that theoretical values for pneumatic actuators should be taken with a grain of salt.

Jason