Has anyone used LINEAR MOTOR COILs for X,Y?

[otto_pjm]

New here, saw these on a surplus site and wondered if anyone has used them? The are not cheap, (motor $90, 22" or 42" track $90), but look quite impressive. Wondering if they have been used by anyone, and if so what your experience was?

Parker Hannifan - Trilogy I-Force #210-2A-NC-WD3S-16 - LINEAR MOTOR COIL


Manufacturers Site.

Surplus site

[Todd Zuercher]

Probably won't have enough force, Most (if not all) motor systems used in CNCs have a fairly large amout of mechanical advantage (gear reduction) used in the drive system, a lead screw or a small pinion coupled with some other gear reduction to get a large number of turns to move a short distance.

[Geof]

Some linear motors can have enough force because they are used on commercial machines. I think your biggest challenge at the DIY level would be measuring position.

[bad bearings]

My understanding is that linear motors require special--and higher power--controls. You might check with Parker.

[NEATman]

Otto-
I have designed and helped build many machines with linear motors. They are most often wired just as any three phase brushless motor is wired, so they will work with brushless motor drives.
The problem comes when you need to close the loop with feedback - typically these are used with non-contact linear encoders such as Renishaw or Heidenhain steel tape or glass scales. I suppose a belt with a rotary encoder would work as well and would keep the cost down.
Keep in mind that you would not need bearing blocks, couplings, ballscrews, other motors, etc. They are also less prone to binding, as all you need to do is keep an air gap around the coil in the track, and they never need lubrication, and they don't wear out.
If you use them for a vertical axis, you WILL need a counterbalance of some kind. We used to use Airpel "anti-stiction" air cylinders with a precision air regulator to dial the Z axis to a neutraly "bouyant" or slightly upward position when the power is removed. That way, if the power goes out your Z axis does not become a guillotine.

Keith

[Andre' B]

Some linear motors can have enough force because they are used on commercial machines. I think your biggest challenge at the DIY level would be measuring position.

This is the only one I have seen in person, and it does move.
http://www.sodick.com/files/library/...eed%20Mill.pdf
A little video.
"http://www.youtube.com/watch?v=DCxZwSwf64U"]YouTube - Sodick High Speed Milling Video

[Mariss Freimanis]

Interesting motors but there is no way to gear them to match a load like you can with rotating motors. Let's compare two 100W motors, one a linear motor and the other a rotating motor:

At 1,500 IPM a 100W linear motor has 35 lbs of thrust. So does a rotating motor driving a 1 TPI screw at 1,500 RPM. The torque needed is 89 in-oz at 1,500 RPM (100W).

Problem is what if you want to trade-in the 1,500 IPM for 150 IPM to get 350 Lbs of thrust? Easy with a rotating motor; use a 10 TPI screw instead of 1 TPI. You have no gearing options with a linear motor.

Linear motors are great for high linear speeds, can't be beat for high rates of acceleration on light loads and the absence of backlash. The biggest disadvantage is the inability to gear the motor (change the force versus velocity ratio).

Mariss

[Andre' B]

Interesting motors but there is no way to gear them to match a load like you can with rotating motors.

Which is one reason such things get expensive, the motors have to be designed and built for the machine they are to be used in to get the best performance.

[otto_pjm]

Thanks for all the replies, I'm looking at building my first CNC router, and the input is much appreciated. I'm thinking about a Joe's 4x4 and want to be able to do some Aluminum cutting so it sounds like more torque and less speed is what I'm looking for based on Mariss's response.

On the location tracking, would it function similar to a stepper, in that you can have encoding and feed back or simply count pulses and tune and control speed such that you don't "skip"? ( NEATman / Keith )

The built in rails and not needing ball screws, v-bearings etc was what I thought was really cool about these, and the ability to just snap in more to extend the track.

Thanks

Pete

[Geof]

Given where I live I cannot resist giving a plug for the longest linear motor system in the world:

http://en.wikipedia.org/wiki/SkyTrain_(Vancouver)

I think I am safe making that claim.

And I think to some extent Mariss' limitation is overcome in the Skytrain motors which use pole switching to change force versus velocity.

[NEATman]

Pete-
The linear encoder used with a brushless linear motor functions just the same as a rotary encoder on a brushless motor. You would need to close the loop around the encoder pulses to get it to work properly. There is such a thing as linear stepper motors but they never really caught on.

I recall a few "exciting" incidents with some of the machines that I designed... Particurlarly when homing for the first time - and the system runs away at max power. Until the following happened, people kept teasing me about how massive the shock absorbers at the end of travel looked.
The most interesting episode was on a machine with 16' of travel and a 9' square vacuum chuck and a moving mass of 4000#. The motor at peak power (4 massive water-cooled coils in one long magnet track) was able to produce about 3000# of thrust. All of the VIP's were gathered to see the huge machine being brought to life, and the guy powering up the machine made a typo in the delta-tau control software which sent full power to the amplifiers. This made the 4000# carriage rocket to the end of travel - directly towards the VIP's - all of whom dove for cover. Needless to say, I was never teased about overdesigning the end of travel stops again. :-)

I attached a close up of the motor & encoder and the insanely complex cable/tubing management. Oh yeah, the frame is the other picture - That is 12" x 12" tubing (1/2" wall) that is 20' long! I also threw in a picture of the granite that made up the lower axis - 3' thick, 4' wide and 20' long (41,500#). The most amazing thing about the granite is that the top is flat to .0005" over the whole surface and one side is accurate to .0004"!

Keith

[Geof]

4000 lb moving mass with a 3000 lb thrust; that would tend to snap you back in your seat. I am too lazy to figure out the speed at which it would hit the end stops but it would be appreciable; somewhere close to 20 mph?

Years ago I tried (unsuccessfully) to get some people interested in designing a linear drive system for firing avalanche charges off the back of a truck.