Electronic speed control valves are available from ProportionAir, Festo and SMC, but they are very expensive - probably over the maximum COTS part price allowed by FIRST.
Here’s a somewhat crude way to electronically control the speed of your cylinder. One throttle valve is adjusted to “slow” speed; the other is “medium”. If both solenoid valves are opened, you get “fast”. This gives 3 speeds. Add more valves to get more speed choices.
Please ignore the backwards arrow on the bottom of the 4/2 solenoid valve.
Yep, that’s a legit way of controlling speed. However, Pneumatic rules change. We used to be able to use two solenoids in series to control the extension of a cylinder. A few years ago, they ruled that such configurations were illegal. Please, check your game manual before trying to use this on a next year’s robot.
I think the only applicable rules this past year were R94A and R95. Basically, you cannot plumb multiple solenoid outputs into one line, and you can’t have any setup that prevents all of the pressurized air from escaping when the manual relief valve is opened. I think the layout posted above would actually have been allowed. (link to rules)](https://firstfrc.blob.core.windows.net/frc2017/Manual/Sections/08-Robot.pdf)
R95 is kind of unnecessary in my opinion. The rules permit you to use pneumatic systems in ways that are just as (if not more) dangerous than plumbing several solenoids to one output.
I think the reason behind R95 was to limit the effective solenoid flow rate, not to make the pneumatic system itself safer. Right now, there is a limit how much air can fit through the solenoids, tubes, and connectors, which limits the speed of the piston (cylinder, whatever). If you have multiple solenoids with multiple tubes right up to the connector in the cylinder, you can increase the speed of the piston, which can be dangerous to anyone unsuspecting nearby.
I’m not going to argue legality. Couldn’t you do this with two valves? Replace the two 2-way valves with a 4-way with your flow controls on the AB ports. Less plumbing, less wiring, less software.
By “applies” do you mean that R95 makes this illegal? If so, how do you figure that? The only plumbing which connects multiple solenoids connects one exhaust to two inputs. Even considering the exhaust as an output (which I would for purposes of this rule), in no volume between the valves are multiple outputs plumbed together.
if I understand correctly.
The design above reduces the flow to the cylinder (by reducing the exhaust flow).
The largest flow to the cylinder can be achieved by letting the air out through the exhaust without any throttling or silencing (for a given supply capacity).
The rules do limit the flow that you can provide to a cylinder, but you can still make a mechanism that holds a cylinder partially extended, fills it with compressed air, and then releases with a mechanical latch to allow full extension. A mechanism like this extends faster than several solenoids feeding a cylinder would.
This was a mechanism used by several teams in 2008 and 2014. I don’t really like it, because it’s a pretty dangerous thing to stick on a robot (just like most launchers from 2008/2014). R95 seems kind of pointless to me when there are permitted ways to circumvent its intent.
I would argue that R95 was not violated because nowhere are the outputs of multiple valves plumbed together. So the letter of the rule is not violated. The intent of the rule is to circumvent the flow restriction of the valves by using multiple valves in parallel. Since the circuit already has the entire flow through one valve, the intent of the rule is not violated either.
Precharging a cylinder against a latch really isn’t more dangerous than using springs against a latch. The cylinders can actually be safer since you can have the cylinders automatically vent on disable.
