Third Year Pneumatic Project.

Projects General Guidance
1

Heey!

I previously posted on here about my animatronic project and everyone who replied was a great help! However things have changed. Im now looking into pneumatics. For my project I'm going to build some exterior cellar doors (of which are padlocked so they will only open slightly) for a theme park prop. I want to make it look as if someone is trying to escape so the doors will effectively 'shake' - so i have chosen to look at pneumatics, but I'm a little confused.

I would like to link up the Arduino to two air pistons and so i have been looking at electronics which i don't really know anything about. I was wondering if there is anyone out there who can advise me on the best way to link the two elements together. I have looked into linking up the Arduino by linking it to a transistor, power supply and relay/solenoid? Would this work? Or will i need anything else in the circuit? - as you can tell I'm clueless.

Any advice/help would be greatly appreciated!
Kayla

2

Interesting project and I daresay some of the mech guys or gals here with have some ideas. I'd look at some of the industrial pneumatics companies, like Festo, to see what they've got.

There's also Mindsets in Herts, not a million miles from Berks, who have all manner of stuff which might give you some ideas. Like this for example although you would need something heftier if those are full size doors.

Jim

3

If they are only fake doors and don't need to open properly you could counter balance them or take most of the load on a spring so that a much less powerful actuator would be sufficient.

...R

4

JimboZA,

Thanks for the links - they look interesting and I have stored them for later reference.

Robin2,

I have been thinking along these lines but until I have my design a little more refined I don’t know if I will use springs (bungie cords) to return the doors back to the home position and use the pneumatics to push the doors open slightly, or use air in both directions to push and pull the doors open and shut. If I can… I wouldn’t mind having both doors controlled individually so that one or both doors can be pushed/pulled randomly for added realism…

Regarding the controlling side of my project - I can see that there will be several parts to the project:

  1. Arduino inputs:

PIR(?) input. This will be used as a trigger to start the shaking of the doors. Triggered when someone walks into the area and
Photo-resistor input: A light source and a photo-resistor to create a light tripwire. Breaking of the light beam starts the shaking of the doors as someone walks through and breaks it. It might be that the PIR starts a light shaking of the doors when someone enters the area but when the light beam is broken it causes a harder/faster/stronger shaking of the doors… or… something else to frighten whoever is in the area.

  1. The code that randomises the output on one or more output pins for a given duration or until the area is clear (i.e the PIR is no longer detecting movement in the area). Dad has suggested that I might be able to also use an output pin on the Arduino to start a ‘screaming’ from a Raspberry Pi as the Pi can play mp3’s through an amplifier - but I don't think I will have time for this.

  2. The electronics/circuit/pneumatics that will be required to take the signal from the Arduino and switch the air of the pneumatics. On the electronics side of the project … I don’t know if I need transistors / mosfets? / relays /solenoids or one of everything? I also don’t know how to wire them up. On the pneumatics side… I will need an air supply/tank (uni has this) tubing, connectors air pistons (double acting?) and some ‘device’ that uses a signal from a relay or transistor to switch air on or off to the pneumatic piston(s)….

Part 3 is hardest part for me to understand…

I have built a couple of projects in the Arduino projects book and with a bit of help off my dad, modified the code so that a led turns on (output turned on) when a torch shining on a photoresistor is removed (to simulate a broken light trip wire). This small project helped me understand quite a bit on how an input can used to create an output and my dad has explained that the input can be the trigger for a random output which can be created in code…. but he has no idea how this can be coded and at this time neither do I.

I would welcome any assistance with the third part (the electronics bit) as it really is totally beyond me at this time.

Kaylaa.

5

Another "outside the box" idea ...

Imagine having a bar (perhaps just a piece of wood) that runs side to side behind the doors. If the bar was shaped (a saw tooth will give the general idea - but the teeth would not be even) then as it slides back and forth it would push the doors open and allow them to close. Variation in the size and spacing of the teeth would give a pseudo-random effect. You could have different bars for each door. The bars could be pushed to and fro by a cheap used car windscreen wiper motor.

A screen wiper mechanism (or two of them) might also be alternatives to a pneumatic system.

...R

6

Pneumatic actuators make some sense here given the short throw and they are what is typically used industrially for this sort of application. You will need pistons as you said and an air source for them. Whether or not you need double acting pistons depends on if you can make the doors close fast enough by themselves or if you need to force them closed.

Working backwards, to control the pistons you need a solenoid valve. You might look at something like what is sold here: http://www.robotshop.com/en/catalogsearch/result/?q=solenoid+valve&order=stats_sales_order_count&dir=desc It would seem like you might be able to get lower prices and more selection at an industrial supplier (Grainger, MSC, etc), but I don't really know what is all out there.

The solenoid you choose will dictate how you drive it. A lower voltage and current solenoid could be driven through a mosfet, while something that uses line voltage or high current would need a relay which you would in turn drive with a mosfet.

As for the sound effects, it sounds like you could use something like this https://www.sparkfun.com/products/12897 to simplify the programming. (granted a Pi is cheaper)

7

a solenoid will be identical to a relay.

there will be a coil, the coil will new voltage and have resistance.

Pneumatic requires volume. so the solenoid needs to have a port size large enough to pass the volume (at pressure) to allow for the piston to be displaced.

if you have a spring return piston, your venting port also needs to be properly sized. your movement will be either full stroke out or full stroke back. I typically use a 3-way with the common to the piston. the NC is to the pressure line and the NO is vent. this gives either a full stroke out or allows a full stroke return.

a double acting cylinder will need two solenoids. it would drive it back faster than a spring. but consume twice the air volume.

if you have a single action, spring return and a second solenoid, you can regulate the speed of the return stroke. or hold the position at any point.

as for wiring them, select the coil voltage, use an N type transistor such as a TIP120. put a resistor between the arduino pin out and the base of the transistor and make sure your power supply can handle the coil on the solenoid. just like a relay, you will need to use a diode to handle the back EMF. just put the 1N4007 or some such, so that it goes from the ground side of the coil to the power side.

wiring is power supply to the coil. coil to the transistor and then from the transistor to ground. the base connects to the resistor and that goes to the pin on the arduino. look at any relay schematic to visualize how to place the diode.

if you want to have some variations, you can have two solenoids. one at 1/3 the port of the other. open the small one and it moves slower. only the larger one and it moves faster. both and it moves rapidly.
you can do this with the exhaust port (dump valve)

another way to control is to use a needle valve with a servo connected. you can adjust air volume in, or out.

sounds like a fun project

8

Don't want to hijack this thread,, but maybe we can learn from each other.

I'm working on a pneumatic project as well, but I'm just using an npn2222a transistor to power my solenoids. The idea came to me from this video Tutorial: How to design a transistor circuit that controls low-power devices - YouTube.

My solenoids seem to be working fine, but I'm not an EE so not sure if I set myself up for ultimate failure yet. I've found many schematics and examples using a relay so I understand where to put the diode in this situation, but I still struggle with where to put in when using the npn transistor as the video doesn't bridge the COM and 12V source of the solenoid power supply like the relay seems to.

9

I think i have found a quick and easy solution to my problems - a relay shield.
http://www.maplin.co.uk/p/relay-shield-for-arduino-n02dh

If I'm right, this should be all I need to connect everything together to make the air pistons work?

Kayla

10

meierk:
Don't want to hijack this thread,, but maybe we can learn from each other.

I'm working on a pneumatic project as well, but I'm just using an npn2222a transistor to power my solenoids. The idea came to me from this video https://www.youtube.com/watch?v=8DMZSxS-xVc.

My solenoids seem to be working fine, but I'm not an EE so not sure if I set myself up for ultimate failure yet. I've found many schematics and examples using a relay so I understand where to put the diode in this situation, but I still struggle with where to put in when using the npn transistor as the video doesn't bridge the COM and 12V source of the solenoid power supply like the relay seems to.

the solenoid is exactly like a relay. any sketch or drawing or schematic is interchangeable.

the only caveat is that you much know the coil voltage and the current.

the resistor between the transistor and the pin is based on current for the transistor to make sure it is saturated.

relay.bmp (29.2 KB)