Firing two solenoids together

[Jon Stratis]

Coming to CD for a little thought experiment...not really an issue for my team, but something noticed during testing.

Say you have two pistons that you always want to fire at the same time. There are a couple of common ways to do this, however each one has its drawbacks. First, you could use a T fitting to plumb both pistons to the same solenoid. They'll fire at the same time, but you're relying on the airflow through that single solenoid to fill both pistons, which may be slower than you want. So, you use two solenoids, one for each piston. Air flow is increased, and you probably just set your programming up to fire them both, one right after the other in the code. In most cases, this is probably good enough.

But what if that millisecond delay from one solenoid command to the next (plus any overhead in sending the messages over two separate CAN xommands) caused a noticeable and troublesome difference in how the pistons move? How do you get around this? Is there a way to sync the commands so the roboRIO sends both of them to the PCM in the same CAN command, and have the PCM updated them both simultaneously? Can you hook up both solenoids to the same port on the PCM so they both operate off the defensible, and program it as though it was just a single solenoid (are there concerns about current draw from a single port, or is it ok?)? Do you switch to controlling the solenoids through a relay, and if so how do you handle 24V solenoid?