Electical coil actuater

[MrWild]

I want to makeanactuater that has a strong pull over a distance of 2.5-3.5 inches. Middle of the stroke at rest and return to middle after the coilis de-energized. Springs will be used for recentering.

I'm thinking Neodymium magnets that traverse inside a hollow coil. Pos/Neg one way makes the magnet go to the right, and pos/neg the other way makes the magnet go to the left. I've picked up some 3/4" dia neodymium magnets and have a stack up of 1-1/8" in length.

The coil spool is being made out of non mgnetic delrin and the cover/housing is nonmagnetic SS tubing. The magnets will be stuck on the actuater rod with some devcon onto a peice of steel dowel that has the other end necked down to 1/4-20 thread for screwing into an aluminum rod.

The supply will be 12 volts and I have 1,000 feet of 24ga. magnet wire.

A few questions. What is the formula for magnetic pull per turn of wire on the spool.

How long should the spool be for 2.5" of travel (1-1/4" each way from center).

How long should the spool be for 3-1/2" (1-3/4" each way from center)

Thanks. Someone asked me if I could design a motorcycle shifter for a disabled Vet, so I'm giving it a shot. My last electro shifter was for me and used passive CRS steel dowels inside a pair of Chevy starter selinoids. Each selenoid activated one side of a heel/toe shifter. Put over 65k miles on that design, but looking for smaller, cleaner, and quieter this time.

[bdhubbard]

It's not quite what you asked, but the linear motors used on old 14" winchester disks are very close to what you are looking for. Surplus?

[Gouky]

if i were making that I'd use an electric lock motor from an early 90's ford truck.

they push/pull very hard and can handle coming to rest at any position in their stroke. they also have about 2-3" of stroke and a mount which is very convenient for what you're trying to do.

[MrWild]

Why did this get moved here? I can see linear motion maybe, but here?

The door lock actuater doesn't center. It is one way or the other. Motorcycle shifters need to home to center in order to work. The lock actuater would need modifications to work. By the time it would be done it'd be a LOT more expensive, almost as much work, and an ugly lump.

I'm sere this forum will come in handy for the momentary high amp switching to make it work with low amp SPDT center off momentary switches. Last shifter design I made used ford starter selenoids to actuate Chevy starter selenoids. An electrical Rube Goldburg, but went 65k miles before I sold that motorcycle. (Thisn was in 95. Friends told me to patent the idea, but whop has $10k for that? Now Honda and Yamaha have it on a few of their bikes.

[vger]

MrWild
If you want something a bit different here is one I came up with years ago looking for someting to use as an actuator for robotics. You would have to add springs to the ends to make it center.

The red is the coil around a brass tube.
The green is steel shell to conduct the magnetic flux of the magnet.
The blue is the magnet (perhaps with end extensions)
The Cyan is brass tube slider.

It's like a speaker voice coil only the magnet moves instead of the coil. Current direction through the coil determines direction.

Best of luck with the shifter.

Steve

[vger]

forgot to insert the image...

[ibwood2]

Here are some sources for the equations that you are seeking.

Biot-Savart equation
Ampere's Law
Lenze's Law

You will need very small wire and lots of turns. The trick is to balance the turns/length of wire/diameter with the current to get a wire size that won't exceed the ampacity of the wire for the desired mechanical output.

Good luck.

[MrWild]

vger, and ibwood,

I'm smiling as I type this. Uh yeah. I've made an actuater in the past for a motorcycle and understand how they work. Very small wire nd lots of turns.... I believe I said I have 1,000 feet (about 320 meters) of 24 ga (very small) magnet wire. I know what a coil carrier and actuater rods do, and how a magnetic field is created for voltage.

Please read what I've said. I am planning on using a neodymium magnet that has a NORTH and SOUTH pole. This way when electricity is induced in one direction, the actuater will go right. and when induced in the other direction, the actuater will go left.

In order to center the magnet portion of the actuater, i know to use springs. In order for the magnet to be the only part that the magentic field affects, I know to either use non magnetic stainless, aluminum or wood for the actuater dowel.

I know the rod should have some support, and the coil carrier should be non magnetic. My coil form/carrier will be made out of delrin. I know all of the simplistic stuff. I was being lazy and wondering if anyone off the top of their heads knew the formula of how many feet/turns will give a general amp load, and magnetic force.

What I'm probably going to do is run an expriment. I'll figure out how many feet it takes of this magnet wire to give me a load that doesn't act like a direct short and then wind it many turns along a spool/carrier/form for a coil of three inches long and see what happens, then go from there.

While I appreciate your help, I'm a little beyond the simplistic beginnings. I'm actually up to "enough knowledge to get myself in trouble." LOL

[Geof]

Originally Posted by MrWild ... I know all of the simplistic stuff. I was being lazy and wondering if anyone off the top of their heads knew the formula of how many feet/turns will give a general amp load, and magnetic force........ I'm a little beyond the simplistic beginnings. I'm actually up to "enough knowledge to get myself in trouble." LOL

I have done a couple of products using solenoids and was up against the same problem...trying to design for a particular force. I came to the conclusion it was real difficult, you can find formulae about ampere-turns and flux density and fancy sounding stuff like that but there are too many variables to apply them is what I concluded. Precisely how close you wound your wires was important and whether you had a steel core or a soft iron core.

I finished up just experimenting until I found something that worked.

Incidentally I was interested in your application. One of my projects was to develop a device to strap on the front of a desktop computer over the power button to turn the computer on via a solenoid actuator switched by a small button switch placed in a location accessible to a user with limited physical mobility. When your computer is on the back of your desk and you are quadriplegic there is no way you can reach up and push that button.

[ibwood2]

24 AWG wire is huge. I was refering to small as 36-40AWG. This will get your turns count up considerably and keep your current draw down. Again look up:
Biot-Savart equation
Ampere's Law
Lenze's Law
For the equations that you need. Thanks for the attitude, Nimrod.

[MrWild]

Originally Posted by ibwood2 24 AWG wire is huge. I was refering to small as 36-40AWG. This will get your turns count up considerably and keep your current draw down. Again look up: Biot-Savart equation Ampere's Law Lenze's Law For the equations that you need. Thanks for the attitude, Nimrod.

Well hey, I guess I'll look up those equations, but as Geof says it will come down to experimentation. I took my basis for 24ga wire from the field coil of a Chevy starter selinoid. It uses even heavier wire. "Really small" is a vague term at best. I'm not a mind reader and to me, the guy that uses 12ga for just about everything, 24ga. IS really small.

As I said, read what I wrote. I stated I had 24ga wire. You said nothing about it being wrong. I said an active actuater in the neodymium magnet. I said delrin spool. You decided I needed a picture of what I already knew and got criptic on what I didn't.

I was actually happy you were helping and tried to show I wasn't being beligerant or ungrateful with my laughing and LOL. Sorry you read it in the wrong tone. I think I'll buy some 36ga wire and see how that works too. My last coil had a high draw and I'm trying to get away from that. Thanks for that nugget of information.

[vger]

MrWild,

Yeah, it's all relative. Now if we could just find "the reference point", you know, that place in the universe that is "At Rest" against which everything is referenced.

I'm assuming you are going after someting like this:
http://www.freebirdcustommotorcycles...ownandhand.gif

That one sells for almost $1,000 (seems a bit pricy to me).

Maybe we could remain calling #24 wire "very small", and call anything in the #26 to #34 "tiny", and then the #36 and smaller "really tiny"... As I stare at what is left of a 1 lb spool of #42 sittin on the shelf . I used that stuff to rewind coils out of vibration pick-ups.

I remember seeing a demonstration once where they lifted a car with an electromagnet powered by a single D cell battery. LOTS of turns of REALLY TINY wire and very flat pole pieces and lifting plate.

Back in the late 70's I built a small X/Y scanner for moving small mirrors for a LASER show. Rather than using springs to keep the shaft "zeroed", I used biasing magnets. The biasing magnets held the plastic shaft (with a magnet epoxied in it) centered and then the applied field from a coil and C shaped form would cause the shaft to rotate one direction or the other based on the polarity. Not sure, but perhaps if you had a donut ring magnet (speaker magnet) around the center of your coil form, you might be able to eliminate the springs. Just a thought

Steve

PS: A brass sleeve around the moving ND magnets will dampen the "ringing" effect.