I've had an idea for a Powerfunctions pneumatic switch which makes use of a couple of Fischertechnik solenoid valves plus a couple of diodes.

The FT solenoid valves cost about $14 each, and are nicely small.

I've attached a drawing of the circuit, and how I think it would work. The limitation I see is that when the stop message is sent to the receiver the cylinder would be floating as opposed to frozen. You might be able to get around this with an alternative pneumatic circuit design? The FT solenoid valves connect the output to the input supply when power is applied and vent the output when power is not applied.

Another idea I had is to supply the constant +9V and 0V to each solenoid valve, thereby making them permanently activated and the cylinder frozen. The C1 and C2 outputs could then be connected via pull down resisters to alternatively ground each solenoid and move the cylinder. I guess they would have to be power resistors? I think the solenoids draw 140 mA when active. Not sure if this particular idea is workable.

If using the PF speed controller you get PWM outputs, and it may be possible to pulse width modulate the airflow, and thereby get variable speed cylinder movement. This depends on the reaction time of the solenoid and the frequency of the PWM I would imagine.

If this all worked it would give 8 switched, variable speed pneumatic circuits to play with, enough to remotely control every function of the 8455 Backhoe loader with its 10 cylinders (I think 7 pneumatic switches + 1 for the compressor?).

Please have a look at the diagram, and if you're electrically or pneumatically knowledgeable give your advice. I reckon that together we could design some cool pneumatic addons without waiting and hoping for TLG to do it.

Thanks,

Tom

Nice idea, waiting for electric specialist, but purists wont like using non-Lego parts, still it would be nice to see it in action!

Have you seen this ?

Have you seen this ?

Yeah, I've come across that before, but was a bit turned off by "due to quality concerns it is withdrawn from general availability".

Interesting what it says about the power booster circuit to provide an initial power spike, and then reduced power (which would presumably sort out the floating cylinder issue on no power). I wonder how compatible it would be with the powerfunctions receiver

solenoid switch has 1 major drawback.

I have thought about it aswell, but the drawback is this:

With a normal switch you have 3 positions, up, middle and down.

But with a solenoid you only have up, and down.

With a normal switch, when you have the desired hight, you put the switch in the middle it stands there.

But with solenoid, the cylinder only got to the max up or max down.

So in the "rest" state the air is not blocked in the cylinder, so the cylinder will go down again.

I have been thinking to solve this by using a servo motor on the Lego switch, and use a small micro controller to control it with the power functions

Edited July 24, 200915 yr by SuperCow

solenoid switch has 1 major drawback.

...

So in the "rest" state the air is not blocked in the cylinder, so the cylinder will go down again.

That is true for the Fischertechniks solenoids because their deactived state is vented, but some valves are normally open, so in the stopped state pressure would be supplied to both ends of the cylinder and it would remain static.

Maybe someone knows of alternative 3 port 2 way solenoid valves that are normally open, and not too expensive?

That is true for the Fischertechniks solenoids because their deactived state is vented, but some valves are normally open, so in the stopped state pressure would be supplied to both ends of the cylinder and it would remain static.

Maybe someone knows of alternative 3 port 2 way solenoid valves that are normally open, and not too expensive?

The Ideal thing would be a three port (not counting vents)/three way solenoid with a spring return to the central position when the power is off. Could a variable valve based on PWM be really that workable? If so then that would be better than great. If not then it's still really great!

The Ideal thing would be a three port (not counting vents)/three way solenoid with a spring return to the central position when the power is off. Could a variable valve based on PWM be really that workable? If so then that would be better than great. If not then it's still really great!

Yeah a 5 / 3 solenoid valve would be great (5 being 1 supply, 2 outputs and 2 vents). Trouble is they seem to be very expensive and not particularly small. Atleast the ones I've seen - I think they're considerably more complex.

but some valves are normally open, so in the stopped state pressure would be supplied to both ends of the cylinder and it would remain static.

do you mean sealed or connected to the circuit? - if connected to the pressurised supply circut at both ends then it is neutral or free floating not locked.

maybe this is useful.

Edit: and this

Edited July 24, 200915 yr by Parax

do you mean sealed or connected to the circuit? - if connected to the pressurised supply circut at both ends then it is neutral or free floating not locked.

maybe this is useful.

Edit: and this

Are you sure? I read that with both ports pressurised the ram would be static, although subject to slight creep, seeing as the surface area on one side of the ram is bigger than the other (because of the rod)

This topic inspirited me to make the power function - servo idea I had for a while.

And guess what, i pulled it off

I managed to make a video with my 2mp camera

What do we see?

At the top its the PF battery box and receiver.

From the receiver there is a cable running to the breadboard with 4 diodes on them.

With this I can read the state with a micro controller.

And from the micro controller I drive the servo motor

The servo is embedded in the Lego piece.

Edited August 9, 200915 yr by SuperCow

Are you sure? I read that with both ports pressurised the ram would be static, although subject to slight creep, seeing as the surface area on one side of the ram is bigger than the other (because of the rod)

It will be free floating [static] not locked [static] so it will have no power and will move if pushed/loaded.

It doesn't matter what the surface area is, if the pressure is the same, then the volume can be displaced...

Try it yourself connect a hose to each end of a cylinder insert T piece and connect to pump.. then try moving the cylinder, then pump up the pressure and try again.. you'll see that as the cylinder moves it pushes whatever volume from one end around through the open hose back to the other end of the cylinder. It doesn't matter what the pressure is because its the same at both ends, the volume will be displaced through the connected pipe at any pressure.

Pneumatics relies on there being a pressure diference between the ends of each cylinder.

P.

Edited July 26, 200915 yr by Parax

Yeah a 5 / 3 solenoid valve would be great (5 being 1 supply, 2 outputs and 2 vents). Trouble is they seem to be very expensive and not particularly small. Atleast the ones I've seen - I think they're considerably more complex.

I suppose if Lego wished to produce a PF valve they could make theirs much some compact as they woulden't have to worry about pressures much above 60psi, bispoke vent ports, 1/4 or 3/8 bsp treaded holes on the three remaining ports or the capability of indutrial amounts of air flow. They could be made much cheaper too by having all the parts made of injection moulded plastic instead of precision machined steel. Sorry iv'e gone a bit off the original topic now

The video posted by Supercow is brilliant!

Outstanding!

Edited July 26, 200915 yr by allanp

This topic inspirited me to make the power function - servo idea I had for a while.

And guess what, i pulled it off

This is quite cool, but I think this can already be done with standard Lego components. You can use the NXT servo motor to measure the state of the switch. The main challenge is to make a switch that is actually small and compact.

I suppose if Lego wished to produce a PF valve they could make theirs much some compact as they woulden't have to worry about pressures much above 60psi, bispoke vent ports, 1/4 or 3/8 bsp treaded holes on the three remaining ports or the capability of indutrial amounts of air flow. They could be made much cheaper too by having all the parts made of injection moulded plastic instead of precision machined steel. Sorry iv'e gone a bit off the original topic now.

Yeah, it can be made of ABS like all the other pneumatic parts. As discussed here a while ago, Lego pneumatics aren't designed to work at more than 30-40psi anyway, and the tubes pop off automatically beyond that.

That's one of my LEGO dreams

Well done trf199 and SuperCow!

Must come back here to read it more in detail, but would prefer anyway a specific off-the-shelf and compact LEGO element, doing the job.

Maybe studies like these, may help pushing TLG to make it by their own.

Nevertheless I'm afraid it won't be small solution... PF IR Receivers are Huge and even the PF actual connector size is quite limiting.