Force output of Solenoids w/ complicated assemblies

[potsked]

I'm trying to guage whether or not a solenoid will be able to produce enough force for my intended application. Most commercial solenoids I see sold fail to produce enough force so I was very interested when I read that complicated and hard to assemble magnetic solenoids can attain much higher flux densities than traditional ones.

Because my application does not demand alot of frugality, paying alot for sophisticated solenoids does not bother me immensely. Optimally, what I'm looking for specifically are force outputs in the range of 300 to 550 newtons from a solenoid that is no larger than 3" x 3" x 8" (cm: 7.5 x 7.5 x 20) So my question would be whether anyone with experience in solenoid engineering knows if something like this is possible.

side note: I'm horrible with the numbers and equations at work in electromagnetism, so please feel free to exclude the math.

Thx for the help

 

[israelkk]

From what distance you need the force?
How much current you can supply?
How much voltage you can supply?

 

[MikeHalloran]

It may have been 20 years ago when Lucas introduced, with much fanfare, the HELENOID, a solenoid with a helical gap. I think they actually got an engine running with the Helenoids operating the valves.

Haven't heard much about them recently.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[sreid]

You might be able to use a voice coil. What's the stroke and is the 550 Newtons continous?

 

[potsked]

sorry, I realized later I left out some info.

The stroke distance needs to be around 3.5 cm or less
As for the current and voltage, the power source will need to be a battery thats portable enough to tote around. Given that it needs to be portable and small/light, the voltage and current will probably be whatever the best configuration a battery can provide. I'm not real familiar with the kind of power batteries can provide so just assume that the battery provides the optimal output that a battery could provide.

*The battery needs to be no bigger than the solenoid.

 

[potsked]

replying to sreid,

The solenoid would probably need to operate at around 35%-50% of the time

 

[sreid]

With the force and stroke you need, battery life would probably be measured in minutes. Have you considered some mechanical arrangemet where you only need power to make the move and then holds position without power?

 

[MikeHalloran]

This is beginning to sound like an application for a ballscrew.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[IRstuff]

dunno... 550N*3.5cm/6V=0.9mA*hr, which is only about 3.2A*s, which seems perfectly tenable.

TTFN

 

[potsked]

sreid: yes the application only requires it to move forward and immediately backward into its resting state, so an arrangement like that would be necessary.

Mike Halloran: don't know what a ballscrew is

 

[MikeHalloran]

We still don't know how fast the device has to move; it would be helpful to know that.

That deferred, 3.5 cm is a _huge_ stroke for a solenoid, even a big one. You need to look up the force/ stroke curve for a typical solenoid; you don't get the solenoid's rated force for its entire stroke.

The primary reason why the force/ stroke curve follows an inverse square sort of relationship is that the effective air gap increases as the solenoid is moved away from the closed position, and magnetic circuits are exquisitely sensitive to air gaps.

A ballscrew is a special leadscrew with friction- reducing balls between the nut and the screw. They can be had packaged with a gearmotor to drive them. An electric motor's air gap, hence its torque, is not dependent on how far the leadscrew has moved. Hence, if the speed requirement is within the capabilities of a motor- driven ballscrew, that device deserves consideration.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[potsked]

when i intoned 3.5 cm or less, the emphasis was on "or less". Preferably, the distance would be as little as possible.

end game purpose is to accelerate a 3 gram object to 90 m/s within a 50-60 ms time frame.

really what im looking for is any knowledge on ultra-high flux solenoids and magnetic assemblies.

 

[IRstuff]

Am I missing something?

90m/s*3gm/50ms = 5.4N That's 2 orders of magnitude off from your original post

The bad news is that the acc=183g's, but it requires 1/2acc*(50ms)^2 = 2.25 m

Assuming that your stroke and velocity requirements are actually correct, I get that you need about 12,000g's and a timescale of 780 microseconds.



TTFN

 

[potsked]

I'm not entirely sure what equations you're working off of, but I used the

F=M*A

and

V_F²=V_I² + 2*A*D

90²=0² + 2*A*.035
A = 115714 m/s²

F = .003 * 115714 = 347 Newtons

that is using a 3 gram object and a 3.5 cm distance. less distance would be better, but more force would be required, obviously.

That clears the math out of the way, but what im really interested in is info on high flux magnetic assemblies.

 

[israelkk]

potsked:

What you forget is the mass of the moving part of the solenoid (the plunger) which will be hundred of grams to achieve this force from a distance of 3.5 cm which you need to get the 90 m/sec speed. You end up with moving a very large mass compared to the 3 grams.

 

[sreid]

How about a rail gun?

http://home.insightbb.com/~jmengel4/rail/rail-intro.html

 

[IRstuff]

The point is that your time scale is incompatible with your desired result.

Per your calculation, you have an acceleration of 115714 m/s^2, this means that 90 m/s is reached in 781 microseconds, not 50 milliseconds. There is no solenoid capable of that kind of acceleration.

To reduce the acceleration requirement is to accept a longer travel distance. Assuming a 50 millisecond acceleration time, you'd only need about 5N and 2.25 m of travel.

TTFN