Advice with electromagnets

I'm doing a project to move a small board up and down and side to side pretty fast. I plan to do the up and down motion with electromagnets and the side to side with a stepper motor.

Is it possible to use 4 small electromagnets to move a 20lb object at around 72 times per minute with a max distance of 1.5 cm? How would I go about doing this if it is the case. Like how would I hook it up and what kind of hardware would I need?

Get some linear actuator that's strong enough to move that 9 kg over 4 cm in 0.833 seconds (including acceleration AND deceleration as you have to start moving it back at the end of that time). It's rather basic physics to calculate the force needed to make that move.
If it's back and forth 72 times, you have to half that time and quadruple that force.
If you have to have it move over that distance at a rather constant force, add a zero or two to that required force.

Hardware you're going to need:

  • some form of pretty beefy linear actuator,
  • a big power supply to match,
  • control hardware (which depends in part on the first two).

To get an idea of the force needed: grab the object (or another 9 kg one that you're allowed to break) in your hands, and try to move it left and right as fast as you can between two points 4 cm apart, No less, no further, no end stops (or you get bounce). I don't expect you can get close to the speed you're asking for with your bare hands.

OTOH, why use electomagnetic force for acceleration and deceeleration alone? Make it all bounce against a spring to get back some of the kinetic energy. Having electricity doing everything doesn't always imply smart design.

Is the object to move the board around or, is it to experiment with the electromechanical aspects?

If moving the board is the focus would not a motor driven rod connected to the board work as well? Think of a car's crankshaft driving the piston up and down.

Johan_Ha:
Make it all bounce against a spring to get back some of the kinetic energy.

I said "without end stops" as OP didn't mention constant back-and-forth movement or controlled movement. I assumed the latter as OP also mentioned it has to be moved in two different directions. Using springs and a constant vibration would indeed make it require a lot less power.

Is it possible to use 4 small electromagnets to move a 20lb object

Well, they'll be small in comparison to the ones used in a steelmaking plant. I would guess that they'll weigh about 20lb each. 4cm is actually a long distance for electromagnets to work on.

Johan_Ha:
OTOH, why use electomagnetic force for acceleration and deceeleration alone? Make it all bounce against a spring to get back some of the kinetic energy. Having electricity doing everything doesn't always imply smart design.

I wish I could but the motion needs to be well defined and precise. I can't have it be inaccurate at all.

wvmarle:
Get some linear actuator that's strong enough to move that 9 kg over 4 cm in 0.833 seconds (including acceleration AND deceleration as you have to start moving it back at the end of that time). It's rather basic physics to calculate the force needed to make that move.
If it's back and forth 72 times, you have to half that time and quadruple that force.
If you have to have it move over that distance at a rather constant force, add a zero or two to that required force.

Hardware you're going to need:

  • some form of pretty beefy linear actuator,
  • a big power supply to match,
  • control hardware (which depends in part on the first two).

To get an idea of the force needed: grab the object (or another 9 kg one that you're allowed to break) in your hands, and try to move it left and right as fast as you can between two points 4 cm apart, No less, no further, no end stops (or you get bounce). I don't expect you can get close to the speed you're asking for with your bare hands.

Would there be a major difference if it were 1.5 cm?

dougp:
Is the object to move the board around or, is it to experiment with the electromechanical aspects?

If moving the board is the focus would not a motor driven rod connected to the board work as well? Think of a car's crankshaft driving the piston up and down.

I need the variability of 0.5 cm to 1.5 cm, on the move. So that I can change the amplitude. That was my initial design but its not variable on the go.

MorganS:
Well, they'll be small in comparison to the ones used in a steelmaking plant. I would guess that they'll weigh about 20lb each. 4cm is actually a long distance for electromagnets to work on.

What about 1.5 cm max? How heavy would you think that to be?

To rephrase my problem. This board needs to go up and down carrying a 20 lb object with a max of 1.5 cm. 72 times per minute. The motion needs to be precise and controlled otherwise there is no point in this. So I can't use springs because I have to know exactly where the board will be at all times.

I'm not talking electromagnets, but linear actuators (various options for this, the simplest being solenoids but those know only two settings: in and out, and some may even only pull and rely on a spring to push).

As it seems you miss basic physics (a bad sign for the rest of the project) here by back-of-a-napkin calculation.

4 cm, 72 times per minute, back and forth, that's 0.4 seconds per movement.
Average speed 0.1 m/s; with acceleration/deceleration top speed 0.2 m/s halfway so reached in 0.2 seconds, that means an acceleration of 5 m/s2. To get a mass of 9 kg to accelerate that fast you need a force of 45 Newtons.
Now go find yourself an actuator that can do some 100 N, and can move at least 4 cm (double the force so it doesn't break so quickly).
A quick Google search turned up this one, it looks suitable. Surprised it's only 10W.

Final note: DO NOT trust my calculation. Check the formulas and calculate again.

Yeah, I never took physics. It's not my project, a superiors, I'm just seeing if it is possible for him and this is a design submitted by another person.

Electromagnets are not necessarily "precise", since there is inertia involved. Another possibility is pneumatic or hydraulic cylinders. Hydraulics are easier to control, since the fluid can't expand or contract. (Air is a spring.)

Generally, "precision" and "control" require feedback. (The control system needs to know the actual position vs. the target position.) Or, in some cases a mechanical stop/limit will do the trick. (The motion of the piston in your car's motor is mechanically restrained, while the speed is controlled through feedback.)

A stepper motor might be OK as long as the speed is acceptable, as long as you don't need "smooth" motion, and as long as the motor is strong enough that it doesn't "slip".

Electromagnets are not necessarily "precise", since there is inertia involved.

That is true, and also a magnetic field strength drops off as the inverse cube of the distance so there is a different force acting on the table at each end of its movement.

this is a design submitted by another person.

Who presumably did not take physics either.

If your 'superior' is paying for this, then it'd be easy.
Moving a 20lb object a few centimeters a little faster than once per second?
Some industrial strength pumps is all you need.

How ever you decide to do it, there will be a lot of heat to be dissipated.

Paul

INTP:
If your 'superior' is paying for this, then it'd be easy.
Moving a 20lb object a few centimeters a little faster than once per second?
Some industrial strength pumps is all you need.

Haha, if only. We do still have a budget. I'm pretty sure he's paying out of pocket to make this work.

I've talked to some people and we're probably going to use linear actuators. If theres any chance anyone knows of a linear actuator capable of holding 10 lbs and moving at a stroke speed of 1" per second under load, that would be great. Preferentially more than an inch and cheap.

Are you mixing 20lb batches of paint? Makeshift ghetto PCR shaker? How large is this object and what shape?
How precise does the movement need to be in terms of distance, velocity, acceleration/deceleration?
There are many ways to accomplish this vague task and if you could get around to telling us what the end goal is (not filtered through your diluted assessment of the project needs) then you can get the best guidance.

INTP:
Are you mixing 20lb batches of paint? Makeshift ghetto PCR shaker? How large is this object and what shape?
How precise does the movement need to be in terms of distance, velocity, acceleration/deceleration?
There are many ways to accomplish this vague task and if you could get around to telling us what the end goal is (not filtered through your diluted assessment of the project needs) then you can get the best guidance.

It moves a 20lb/9kg box up and down. The exact, or near exact, position of the box must be able to be accounted for at all times. The velocity, acceleration, and etc. do not matter in accuracy. All I require of it is to be able to move 72 times per minute all the way from 0 cm to a maximum of 1.5 cm and I need to be able to adjust the distance in between. It needs to accomplish this very close to 72 rpm. So I guess acceleration does matter. If the speed differs too much it will be unusable. I also need it to be variable. Not in immediate change in distance of 0 cm to 1.5 cm. But I need to able to control the distance the box moves, and track it, electronically and from a distance. I cannot have access to it once it starts. I hope that is enough, please let me know if you need any more. I'm willing to use anything. Also, it cannot use a single motor with metal of any kind, directly in the middle of the box. The motors must be near the corners of the box. Unless of course there is a way to have no metal near the middle/ the motor a distance away from the middle

Still not answering what you're making. Must be super duper top secret free energy machine.

INTP:
Still not answering what you're making. Must be super duper top secret free energy machine.

Well, that is literally its purpose. To move a box weighing up to 20 lbs. Is there any more you really need? It won't change the outcome. The box is either a cube or a rectangular prism.

Is there any more you really need? It won't change the outcome.

It might. You might actually get some help.

Hi,
Are you mixing something?
Are you vibration testing something?
Does the action have to be linear?

Tom.. :slight_smile: