I think vex should sell a solenoid motor because its cheap easy linear motion. The pneumatics are the only thing they have right now but they are kind of expensive.
Sorry for the short post, I was in an airport and my flight was boarding so I had to make it quick!
But anyway I was thinking that they could use the standard motor case but they could shorten its height by half and double the width. Then you could fit a fairly decent size solenoid in the case with the circuitry and a capacitor (For the initial push). It should have a travel of at least 1in with spring return or just reverse the polarity if possible (I will check on that). They should be able to offer different travels say 1/2in, 1in, 1.5in, and 2in.
I can see a lot of uses for this because the pneumatics are A.Really expensive B.Large (Air tank valves ect…) Although the solenoid won’t put out 12lbs of push like the pneumatics at 100 psi it should be enough for at most 1lb of push. That should be enough to switch gears or push buttons.
I may be wrong about the amount of push this could have but it really matters about how much current you can draw and the size of the solenoid. I think the most you can get from the micro controller is 2 amps so this could possibly have a battery connector built in so it could draw 5 or so amps.
Tell me what you think!
I think this is a great idea, and I’d buy a set the first day they go on sale!
I think you won’t get the amount of travel/power you mention above. Most solenoids with any power only travel a small fraction of an inch (1/8", 1/4", etc). Solenoids with longer throws tend to be much weaker. Some of them are specified with a curve, such that it has a stronger pull the closer it gets to fully-retracted. This is just a result of the way the magnetic field gets weaker the further the plunger gets from the center of the coil.
BTW, I have used solenoids with Vex for a haunted house. I used a digital-out port to drive a transistor, which ran a relay, which controlled a big honking solenoid. A program watched an input driven by a motion sensor and then pulsed the solenoids with a pre-coded sequence. When you walked by, the solenoids violently rattled a door like something evil really wanted out. I think we had several people need to change their underpants that day 
Great idea!
- Dean
That’s the problem with solenoids is that they get weaker the farther the armature travels. Pneumatics have pretty much the same amount of power for the whole stroke aside from when you first turn on the air and it only needs higher pressure and a larger surface area of the piston to be more powerful. Solenoids need more current and voltage and when you increase those 2 things the wire will get hotter and have a lower duty cycle so you have to use a bigger gauge wire to prevent it from getting hot.
Solenoids only need a battery or wall outlet (AC or DC) to operate and a switch pneumatics need a lot of support to run which adds up to $$$$ like the regulator, 4 way solenoid valve, hosing, air supply, and valves. So I guess there is certain pro’s and con’s of each.
you wouldn’t need much distance if you were going to use a solenoid to lock gears. (would have made hanging on the bar in 07 a lot easier)
Ooh, a solenoid clutch assembly…
- Dean
Quazar,
Could you post a diagram of the relay circuit that you used to control the solenoid. I am working on a very similiar project. I am looking for a way to control 120V solenoid valves using vex. Part Numbers would also be greatly appreciated.
Thanks,
-Brando
Sure, I can whip something up. It was basically just two of this circuit with a 12VDC relay driven by each transistor.
There was a 12VDC power supply that provided power for the relays and for the VEX Microcontroller (through a 7808 voltage regulator).
I’ll try to post a diagram later today…
- Dean
All you really need is to use a motor driver or the circuit that Quazar posted to drive a relay.
The relays should have a 6 to 12v coil voltage with a 120v ac load voltage with about a 1amp current rating for solenoid valves. If you are driving something else you need to check how much current it draws and get a relay capable of that.
But if you are using it for air or water solenoid valves as you said I can’t see it drawing more than 1amp but just to make sure I would get a 5amp relay to be 100% sure that you are safe.