Multiplex Festo Valves

[C3PO]

It appears that only four FESTO valves (8 solinoids) can be driven by the 24V breakout board AND only one breakout board can be used in the robot. Does anyone know if it's legal to to multiplex the 24V breakout board lines via additional relays driven via the digitial side car relay drivers? In other words, one 24V line from the breakout board would be used control both of the solinoids on the Festo Valve.

Any thoughts would be greatly appreciated.

C3PO

[Al Skierkiewicz]

C3PO,
I seem to remember that the 24 volt supply on the PD cannot supply enough current for more than 8 solenoid coils.

[PAR_WIG1350]

<R45> All electric power utilized by the ROBOT shall be distributed from the load terminals of the Power Distribution Board. Circuits may not bypass the Power Distribution Board to connect directly to the 120-amp loop.
A. The cRIO-FRC power input must be connected to the 24 Vdc supply terminals on the Power Distribution Board. With the exception of one Solenoid Breakout Board, no other electrical load can be connected to these terminals.

This rule only says that a maximum of one solenoid breakout can be powered with 24 volts, I can find no rule that would stop you from using a second, 12 volt breakout. See if you can make your pneumatics system work with 12 volt solenoids instead.

[EricVanWyk]

You can actually use 2 solenoid breakouts, this was addressed in an update. Up to one of these can be 24V.

Al is (as usual) correct. You can not drive >8 24V valves with the 2010 control system. It is both illegal and there is not enough headroom in the 24V supply to do so.

[C3PO]

Thank you all for your wonderful help. We don't plan to use more than 2 FESTO solonoids at any time. So, I think the 24V supply would provide plenty of power. I'll look at the updates for information on additional 24V breakout boards.

Again, many, many thanks.


C3PO

[DonRotolo]

So, I think the 24V supply would provide plenty of power.
The experts say it won't, perhaps you should reconsider?

[C3PO]

Hi Don

Gulp,……the 24V breakout won’t provide enough power to drive two (2) solenoids simultaneously? In other words, only one half of a Festo valve (one solenoid coil) can be driven at any time? If this is true, we are doomed.

C3PO

[EricH]

I'm pretty certain it will run 2 at a time. I'm fairly certain it could run 8 at one time.

But what you're asking is if there is a way to get it to run more than 8 at one time. That's not legal, and there isn't enough oomph in the 24V supply to do it. (See EricVanWyk's post.)

Now you're looking into using a second 24V breakout. That is also illegal. <R45-A> makes it clear that only one solenoid breakout and the cRIO can go into the 24V terminals on the PDB.

Your best bet is to find a bunch of 12V solenoids and run those on a 12V breakout, or through a Spike run by the relay board.

[EricVanWyk]

Hi Don

Gulp,……the 24V breakout won’t provide enough power to drive two (2) solenoids simultaneously? In other words, only one half of a Festo valve (one solenoid coil) can be driven at any time? If this is true, we are doomed.

C3PO

C3PO -

There is some miscommunication occurring here. My understanding of your situation follows. If it is incorrect, ignore the rest of the post:

You have more than 8 solenoids that are 24V, but you only need to activate up to 2 at any one time.

This is do-able from an engineering point of view. The 24V supply can most certainly power 2 valves at once, and it doesn't matter how many valves you aren't using. Great. However, the rules prevent this. Since the penalty of trying to power >8 valves at once is that your robot reboots and you likely lose the match, the rules are written conservatively. I strongly agree with (and proposed) this conservatism.

In post #5, you spoke with respect to tech, but Don responded to you with respect to rules. You interpreted Don's response as if he was also talking tech, which resulted in the confusion.


Long story short, use up to 8 24V solenoids. All other solenoids will have to be 12V. If you wish, request a change for 2011.

[C3PO]

My apologies for the confusion. In a nut shell:

1. I wish to control a MAXIMUM of two(2) Festo solenoids at ONE time.
2. I wish to multiplex each of the 8 24V solenoid breakout lines with a SPDT relay driven by the digital side car so that the 24V breakout line can connect to either Festo of the two valve solenoid coils but only ONE at at time.
3. This would allow the control of 16 Festo solenoids (8 complete valves) as long as power only two solenoids are energized at any one time.

My question is ....................Is the multiplexing legal?


C3PO

[EricVanWyk]

My question is ....................Is the multiplexing legal?


Nope.

[C3PO]

Thank you all very much for helping me with this. I really appreciate your input and patience.

May the force be with you all,

C3PO

[PAR_WIG1350]

My apologies for the confusion. In a nut shell:

2. I wish to multiplex each of the 8 24V solenoid breakout lines with a SPDT relay driven by the digital side car so that the 24V breakout line can connect to either Festo of the two valve solenoid coils but only ONE at at time.


C3PO


<R46> All active Power Distribution Board branch circuits shall be protected from overload with an appropriate value auto resetting Snap Action circuit breaker (from the KOP or identical equivalent).
B. Each Spike relay module branch circuit must be protected with one and only one 20-amp circuit breaker on the Power Distribution Board. No other electrical load can be connected to the breaker supplying this circuit.


I think this prevents using 24 volts with the spike relays, the only legal relays.
Also,
<R65> Solenoid Breakout outputs shall be connected to pneumatic valve solenoids only. No other devices shall be connected to these outputs.

I believe that this prevents relays from being used to switch solenoids controlled by the breakout.

[Al Skierkiewicz]

Alan et al,

This is the more pertinent answer:

<R45> All electric power utilized by the ROBOT shall be distributed from the load terminals of the Power Distribution Board. Circuits may not bypass the Power Distribution Board to connect directly to the 120-amp loop.
A. The cRIO-FRC power input must be connected to the 24 Vdc supply terminals on the Power Distribution Board. With the exception of one Solenoid Breakout Board, no other electrical load can be connected to these terminals.

[DonRotolo]

Al,
I think more relevant is <R03> Custom circuits and COTS electronics are expressly PROHIBITED if they:
A. Interfere with the operation of other ROBOTS.
B. Directly affect any output devices on the ROBOT, such as by directly powering a motor, supplying a PWM signal directly to a speed controller or supplying a control signal directly to a relay module (see Rules <R63> and <R64> for the specific exception regarding CANbus devices). (emphasis mine, also below)
Which, when combined with <R50> Custom circuits shall NOT directly alter the power pathways between the battery, Power Distribution Board, speed controllers, relays, motors, or other elements of the robot control system (including the power pathways to other sensors or circuits). <snip>
prohibit using a relay to alter the control path to a solenoid valve. Thus Eric VanWyck's succinct response.

Of course, it IS legal to use 24V to power solenoids as you quoted.

[Al Skierkiewicz]

Don,
I was responding to using 24 volts to control solenoids through Spikes. Sorry for the confusion.

[Joe Johnson]

MAN!!! Up until yesterday night I managed to ignore the pneumatics rules and caveates.

When they had issues, I assumed that it was simply a matter of the folks on my team not reading the manual(s).

Now I see what a morass that the pneumatics really are. From finding the right valve to order to staying legal to drive voltages to relief valves to M5 fittings to Kansas City and Back again... ...this stuff is simply not easy.

There are a lot of advantages if you get through the learning curve (and then stay ahead of the changes), but whoa, I don't know how mere mortals (i.e. about 50% of the FIRST Teams) can do anything much beyond using the stuff in the kit as is and ordering a few Bimba's...

Joe - the mortal - Johnson

[Mark McLeod]

I don't know how mere mortals (i.e. about 50% of the FIRST Teams) can do anything much beyond using the stuff in the kit as is and ordering a few Bimba's...
You need to look more closely at what comes in the Kit.
Teams can't actually put together a pneumatic system from the Kit anymore.

[Daniel_LaFleur]

You need to look more closely at what comes in the Kit.
Teams can't actually put together a pneumatic system from the Kit anymore.

Yeah,

I was rather surprised to find no tube fittings at all in the kit.

[JamesCH95]

Don't ever run 24v through the SPIKES, legal or not they will fry in an instant.

[Joe Johnson]

Don't ever run 24v through the SPIKES, legal or not they will fry in an instant.

Depends on what you mean by "through" I think that on they are just standard dual SPDT relays typical of what is used to drive a window or seat adjuster on a car. I don't have one in front of me, but I would be surprised if they had any practical issue switching 24V -- there may be some life issues or some arcing inside the relay that is less than ideal but I am pretty sure that they are standard automotive relay which is to say that 24V will definitely not cause them to "fry in an instant"

Now, the control circuitry, that is another matter entirely.

24V may in fact cause something on the control circuit to fry in a New York Minute -- which everyone knows, is an order of magnitude LESS than an instant ;-)

Cheers,
Joe J.

[JamesCH95]

I have hooked up SPIKEs to 17-19 volt sources, not the signal, for NON FIRST projects. You'll hear a little pop, and the relay will never work again. =shrug= doesn't matter what part of the spike breaks.

[Joe Johnson]

I have hooked up SPIKEs to 17-19 volt sources, not the signal, for NON FIRST projects. You'll hear a little pop, and the relay will never work again. =shrug= doesn't matter what part of the spike breaks.

Ah, you remind me now. Getting old sucks* I forgot the driver circuit on a Spike is co-mingled with the power circuitry.

The coil on the relay draws its power from the hot side of the power circuitry. I think that the Spike has an onboard Darlington pair of FETs that provides a path to ground from the hot side of the power voltage through the coil of the relay. The "PWM cable" is nothing but a means of turning on the FETs.

Anyway, it is this circuitry that must not tolerate the higher voltage.

This is unfortunate for a several reasons but it is what it is.

Sorry for the bad info.

Cheers,
Joe J.

*well... ...only when you don't really consider the alternative.

[Al Skierkiewicz]

Joe,
I believe there is a 5 volt regulator for control circuitry fed from power input and the 12 volt raw power supply feeds the relay coils. There is also an opto coupler pair that couples the relay control signal into the box.

[billbo911]

I have hooked up SPIKEs to 17-19 volt sources, not the signal, for NON FIRST projects. You'll hear a little pop, and the relay will never work again. =shrug= doesn't matter what part of the spike breaks.

According to the IFI Spike page (http://www.vexrobotics.com/products/vexpro/spike-relay-h.html), this "H-Bridge Relay" is capable of running on 6vdc-16vdc. It sounds like you may have pushed it just a bit too hard.:o

Sorry, no schematic was available on that page.

[JamesCH95]

It would make sense that the v-reg fries. IIRC (it was 5 years ago that I took one apart) everything on the PCB is potted up in epoxy, so replacing a component that get's cooked isn't an option.

[Holtzman]

MAN!!! Up until yesterday night I managed to ignore the pneumatics rules and caveates.

When they had issues, I assumed that it was simply a matter of the folks on my team not reading the manual(s).

Now I see what a morass that the pneumatics really are. From finding the right valve to order to staying legal to drive voltages to relief valves to M5 fittings to Kansas City and Back again... ...this stuff is simply not easy.

There are a lot of advantages if you get through the learning curve (and then stay ahead of the changes), but whoa, I don't know how mere mortals (i.e. about 50% of the FIRST Teams) can do anything much beyond using the stuff in the kit as is and ordering a few Bimba's...

Joe - the mortal - Johnson

While we're on the topic of silly pneumatics rules, I'd like to direct your attention to this q&a posting.

http://forums.usfirst.org/showthread.php?t=14428

Basically, my understanding of it is that the Festo valve we got in the KOP doesn't meet the requirements of <R72-C>.

C. Solenoid valves. All such valves must have a maximum ⅛” NPT port diameter, and a maximum Cv of 0.32 (if non-KOP valves are used, the team will be required to provide part documentation validating that the valves meet these constraints).

But, <R30-A> states that anything that comes in the KOP is legal. So, we are allowed to use the one FESTO Solenoid that came in the KOP, but we can't use more than one of that particular solenoid, since valves in addition to ones provided in the KOP must meet <R72-C>.

[JamesCH95]

I think the intention of that rule is to allow the use of duplicates of KOP parts.