Using more than 8 24v solenoids

Our team has always used 24v solenoids, as such we have a reasonable stock of them. At this stage it looks like our robot will require more than the 8 channels usually available on the Solenoid Breakout.

I have a few ideas to get around this, but I wanted CD’s thoughts on this:

  1. Split air AFTER valve, ie run two cylinders off one valve, this is the simplest but does waste air. However AFAIK is completely legal.

  2. Split electrical signal AFTER breakout and BEFORE valve, the only relevant rule I could find was [R51]

Unless otherwise noted, each power regulating device may control one and only one electrical load.
However a strict reading of this table implies that the Solenoid Breakout can only control one solenoid. Is it worth Q&Aing this?

  1. Splitting 24V supply AFTER PDB and BEFORE breakout such that two Solenoid Breakouts are used. Illegal under [R42]:

With the exception of one (1) cRIO and one (1) Solenoid Breakout Board, no other electrical load may be connected to the 24 VDC supply terminals on the PD Board.
However [R69]:

If powered from the PD Board 24V supply per R41, loads on each Solenoid Breakout shall not cumulatively exceed 16W if using the cRIO-FRC (8-slot) and 21W if using the cRIO-FRC II (4-slot).
is worded with “each” which could be inferred to mean more than one. Regardless [R42] seems fairly clear cut. Is it worth Q&Aing this?

  1. Use some 12V solenoids. Not preferable, for obvious reasons. But AFAIK legal.

  2. Completely switch to 12V. Less preferable than 4, but will be less complicated. Definitely legal.

1, 4 and 5 are the most likely options. 2 and 3 while technically possible (assuming compliance with [R69]) are questionable at best, and probably illegal. So I’m stuck between two bad options and two illegal ones.

Is there anything else that I’ve missed? Any other ideas?

How does 1 “waste” air? All of it is doing work.

  1. Redesign things to need fewer cylinders, using motors and other choices.

However, I agree, IMHO 4. is a good choice.

Don’t you have room for a second breakout board? You could even run 8 solenoids at 24v and 8 more at 12v.

What are the “obvious reasons”?

As another potential option (you would want to Q&A it), what about having an independent 24V converter to power the second solenoid module? It would plug into one of the 20A breakers. I’ve never seen it done, and from a quick reading of the relevant rules I’m not sure which way the GDC would fall on…

AFAIK you are allowed to (at least with the 8 slot cRIOs you can/could)

That would be illegal per R53.

Are you using two position (toggle) solenoids or one position (hold-on) solenoids? You can cut the number of channels you’re using in half by using the latter of the two (depending on the application of course).

The unwritten rule of thumb on our team has generally been “If you need more than 8 solenoids, you probably have too many pneumatics on the robot”.

We have always designed to minimise the tubing between the valve and the cylinder, as air in tubes between them is dumped when the valve is cycled, ie. the air in the tubes don’t contribute to the force, but is still used up. Is this correct? Or am I being over-conservative in the volume wasted?

We’d like to avoid mixing inventories, if there are no 12v solenoids to plug into the 24v breakout, then it can’t happen.

My favourite option, however Mech doesn’t agree.

We are using 5/2 solenoids, (specifically these I’m under the impression that one position solenoids return to the home position when the robot is disabled, as such we have discounted them for safety reasons in our application, is this correct?

Joe and Jon,
I believe the custom circuit 24 volt power supply would be considered legal under the current rules but this is a question that needs to be asked of the Q&A. Under all circumstances, the power limits on the solenoid modules under R69 must be met. I think that R40 was written to allow this and to prevent line voltage inverters.