I need a push/push electro magnet

T Chap

I need to build a system that will push an object approximately 2-3 inches, and then pull the object back at a later time. The forced needed to push and pull the object may range from 5 - 10lbs. It will probably need to have some PWM control so that it is not so abrupt, and the motion can be ramped a little to avoid a collision, it can't run just full on or full off. There are numerous electromagnet examples online with a coil wrapped around an iron rod.

Some questions I need to solve tomorrow:

Will this require that the object being moved have a permanent magnet on it so that positive and negative force can be exerted on the object by flipping the current?

Will driving the magnet with 24vdc and a mosfet off a Prop be able to move the object. I am assuming that the magnet will behave just like a motor, requiring the polarity to be swapped on the coil for each direction.

How much magnet wire(length) would be required to exert 10 lbs force?

Thanks for any suggestions before I head out to find parts to test this out.

BTW The reason I can't just use a stepper or DC motor instead is that once the object gets pushed out by some force, other parts of the system will push the object several feet away by a motor, and syncing two motors together would be a big hassle, even kicking off the stepper or DC motor will put too much drag on the system. At some point the object returns to within 2-3 inches of its original starting but, but needs some assistance getting back to zero.

Beau Schwabe

T Chap,

You didn't say how fast you wanted to move 2-3 inches. Technically a motor is an electro-magnet.

And the pulling or pushing won't be on an incline of any kind? ..because pulling or pushing is a lot different than lifting.

T Chap

Beau, the speed is pretty slow, I would say that the 3 inches of push or pull would be 2-4 seconds. The object is on a track on wheels, so the motor or magnet is not picking up anything, just sliding it over.

Beau Schwabe

I sent you a couple on PM's...

T Chap

Thanks Beau. Here is a photo that shows better what I need to do. A solenoid would be too loud. I need something quiet, and preferably not another motor to sync up. The photo shows a slide mounted on a horizontal rail, the slide needs to be pushed to the left to start a motion that another motor completes. Then when it returns to within a few inches of the start point, the magnet or other method helps out by gently pulling the slide back into place.

Once the slide is moved over a few inches, another motor elsewhere in the system causes the slide to move much farther down, so the travel is not limited to 3 inches, only the "assistance area" the slide needs.

erco

Electromagnets have an iron core, so a PM will always be attracted to it, even with no current flowing through it. You can get a bit of repulsion with a LOT of current to make the same polarity as the PM, but if the PM touches and sticks to the iron core, you'll never generate enough electromagnetic force to drive it away. That's been my experience, anyway.

kwinn

An electromagnet (solenoid) is probably not suitable for this. The motion is too rapid (consider it a bang-bang motion). A motor and screw/belt type mechanism would be a better choice.

Dave Hein

T Chap wrote: »

BTW The reason I can't just use a stepper or DC motor instead is that once the object gets pushed out by some force, other parts of the system will push the object several feet away by a motor, and syncing two motors together would be a big hassle, even kicking off the stepper or DC motor will put too much drag on the system. At some point the object returns to within 2-3 inches of its original starting but, but needs some assistance getting back to zero.

Can't you just use a servo to push the object out a few inches? Pulling it back would be a bit more complicated. You would probably need a second smaller servo to lower a hook to grab the object, and then raise the hook to release it.

Dave

Beau Schwabe

My PM question still stands...

---

Is this an inertia issue with the drive motor? If you look at your system as a "T" where the drive motor is in the top of the "T" and the breakable panels are in the stem of the "T" do you have to go on both sides of the "T" to break the panels or could it be configured in an "L" using just one side of the "T"? The reason I ask if it's an inertia start/stop issue, then changing the angle of "L" slightly to make it acute (less than 90 Deg) might be enough to overcome the start /stop inertia when the panels need to be straight.

If that's not the case however, you have a greater moment arm from the 'breakable panels', meaning that you would need less force to move the panels then trying to move the drive motor. In this case a magnet mounted in each, or just a few 'breakable panels' that align with a coil(s) placed on the track might work. The size and number of windings would be subject to experiment, but if you wanted something that would not interfere with the track itself, I would maybe start with two smaller coils mounted on either side of the mechanical track or guide that are configured opposite polarity of one another and wired so that they would both come 'on' at the same time, so one would effectively push at the same time while one would effectively pull. All of the coils would be Air-core <- so when they released, there would not be a potential for the magnets in the panel to 'hold' a position under the coils.

kwinn

This is about the simplest and cheapest mechanical system I can think of to do what you want. The drive motor could be a stepper or dc motor, and the belt and pulleys are available from most industrial suppliers. An auto parts store might even have something similar.

T Chap

Thanks for the suggestions guys. I really did not want to add another motor and timing belt, there already is one and adding a second means more hardware, costs, etc. If I can't find a simple push/pull magnetic approach then the motor/belt idea will be the last resort and is easy to do, the rest of the system already has that system in place.


@Beau

It is an "L", the motion perpendicular to the main drive belt and motion is only on one side. So the slide that I want to assist is only on the horizontal part of the L, only at the junction of the stem of the L. As far as inertia, it is not an inertia issue to break the panels, as the main drive cannot break the panels apart until the slide shown in the photo is first dislocated from it's Zero position. The same applies to returning the slide to Zero to park, the system mechanically is not capable of moving the slide back to home, so in neither case is it a matter of inertia moving the slide. I hope I answered what you were asking, I may not be completely clear though. It is not possible to allow an angle to exist to prevent the 'locking' of the system.

tonyp12

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