- #1
Anachronist
Gold Member
- 117
- 47
I'm trying to come up with a lightweight solenoid linear actuator, by constructing two electromagnets that telescope. The outer coil would be wrapped around a soda straw, and the inner coil would fit inside the soda straw and be wrapped around something smaller, like a bamboo skewer (which also serve as the actuator shaft).
Well, I'm wondering about the pushing or pulling force this thing can impart. The force of an electromagnet on an object would be
$$F=\frac{(N I)^2 \mu_0 A}{2 d^2}$$
where ##N## is the number of turns, ##I## is the current, ##A## is the cross-section area of the coil, and ##d## is the distance between the open end of the coil and the object.
If the object is another coil of a different diameter and windings, but with the same current, the force would be
$$F = \frac{\mu_0 I^2}{2 d^2}(N_1^2 A_1 + N_2^2 A_2)$$
This looks like it would blow up when ##d=0##. And what would be the force when one coil is partially inside the other? I would think it would be less, going to zero when one coil is completely centered inside the other.
If my objective is light weight, is this even efficient, or would it be more efficient to use a strong magnet on the end of my rod?
Also, if I'm limited to, say, 0.3 amps, it seems like I'd need a lot of windings just to get 30 or so Newtons of force, and that's right at zero distance, with hardly any force seen if the actuator moves even a little bit.
Well, I'm wondering about the pushing or pulling force this thing can impart. The force of an electromagnet on an object would be
$$F=\frac{(N I)^2 \mu_0 A}{2 d^2}$$
where ##N## is the number of turns, ##I## is the current, ##A## is the cross-section area of the coil, and ##d## is the distance between the open end of the coil and the object.
If the object is another coil of a different diameter and windings, but with the same current, the force would be
$$F = \frac{\mu_0 I^2}{2 d^2}(N_1^2 A_1 + N_2^2 A_2)$$
This looks like it would blow up when ##d=0##. And what would be the force when one coil is partially inside the other? I would think it would be less, going to zero when one coil is completely centered inside the other.
If my objective is light weight, is this even efficient, or would it be more efficient to use a strong magnet on the end of my rod?
Also, if I'm limited to, say, 0.3 amps, it seems like I'd need a lot of windings just to get 30 or so Newtons of force, and that's right at zero distance, with hardly any force seen if the actuator moves even a little bit.