Using 3 phase AC motors for platform

[Dutchboy]

Ok, I'm in the middle of the concept stages of my motion platform. I have done quite a bit of research, and found that most of the professional electric motion platforms use powerful 3 phase AC motors.

So, considering it would be easy to add a single phase 240v/60hz line in my basement and use single phase input to 3 phase output motor inverter controllers, does anyone see a downside to using 3 phase vs. low volt DC?

This is similar to what I would like to build:
[ame="http://www.youtube.com/watch?v=UDtb8lePiys"]YouTube - Cal Poly Flight Motion Sim In-Action[/ame]

Thanks,

Dutchboy

[Roland]

It all depends on whether you're going to build or buy, and your budget.
Low voltage DC motors are relatively easy to drive with either homebuild MOSFET drivers or low cost commercial avaliable drivers. Low / medium power DC motors are not that expensive either. As you mentioned you're going to build a single seater small GA platform, the DC motor power requirements would be OK.

With 3-phase motors, your only option is buying and my guess is that prices will be stiff.

[Dutchboy]

Thanks for the reply Roland. I have actully found some 3-phase motors (inline gearmotor, 1/4 hp, 125rpm, 120 torque in-lb, continuous duty) for $170 US each.
http://www.surpluscenter.com/item.as...tname=electric

The controllers I was thinking about are about $120 US each.
http://www.surpluscenter.com/item.as...tname=electric

So, in total, around $900. Not bad. I may look for something with a little more power though.

Dutchboy

[AndyT]

Another thing to factor in is that when you build the platform you design in 'balance' so that the whole works needs very little power to move it. And if you set the balance point taking into account the weight of the pilot and Copilot (if the sim is that big) then you really do not need that much power. Most of the sims you see running motion on this site are using very small DC motors. (under 1 hp) The 3 phase motors you are looking at are OK, but the electrical considerations for them adds to the overall complexity of the project.. A general rule of thumb for motion, the smaller and simpler you can get by with, the better.

I personally am using two 12v wheelchair drive motors controlled by a Phidgets servo controller. So far I have not decided on software but since I'm running FSX I just might have to write my own. (Hey Alan!, hint hint)

If you really want lots of power, then look at winch motors. They run 12v and can pull a ton or two depending on the winch.

[Dutchboy]

Well, I am thinking of moving to a 3 DOF platform, in which I would need the power to lift the platform to create heave. This would require more than low power DC if I wanted it to be fast. I'm sure I could use winch motors if I didn't care how fast it was. The more I think about it, the more I think 3-phase is the way to go for what I want. It really isn't that hard to wire those controllers to the motor. Especially because those controllers only need 240v single phase input.

The cost of 3-phase isn't that bad if I go for 1hp or less. I'll stick to the PWM controllers and user a servo control board. I should be able to do this for around $1500.

I'm fine with the cost being a little higher if it means more speed and the addition of heave.

Dutchboy

Another thing to factor in is that when you build the platform you design in 'balance' so that the whole works needs very little power to move it. And if you set the balance point taking into account the weight of the pilot and Copilot (if the sim is that big) then you really do not need that much power. Most of the sims you see running motion on this site are using very small DC motors. (under 1 hp) The 3 phase motors you are looking at are OK, but the electrical considerations for them adds to the overall complexity of the project.. A general rule of thumb for motion, the smaller and simpler you can get by with, the better.

I personally am using two 12v wheelchair drive motors controlled by a Phidgets servo controller. So far I have not decided on software but since I'm running FSX I just might have to write my own. (Hey Alan!, hint hint)

If you really want lots of power, then look at winch motors. They run 12v and can pull a ton or two depending on the winch.

[Roland]

The prices at surplus center aren't bad at all.
Had a look at the specs of the motors: If you want the 3 motors to carry the full weight of your platform, (say 120kg like mine) each motor would have to sustain 40kg. The torque of the motor says 120 inch-lbs which is 13.6Nm. with arm-length of 0.2m you would get 68N of force which can lift only 7kg. So it won't work for a non balanced platform.
If you use a big spring to offset the platform weight, it will still be critical, as depressing the spring also takes extra force. Seems that the torque of the motor is not sufficient (or maybe I made a mistake, I can only calculate in metric)
Just for reference: My homebuild actuators produce ~ 43N of force per Ampere. At 10 Amp, 430N gets a balanced 120kg platform really moving!
I use pulley / belt system for gearing as it can take lots of abuse. Standard gears don't like sudden reversal at high torque.

To avoid dissappointments, make sure you do these kind of calculations before you buy!

[Bob Reed]

I think as well keep in mind most commercial platforms are hydrolic so the 3 phase motors are driving hydrolics.

[Dutchboy]

Perhaps you guys are right. I just saw this sim and got excited about the power:
[ame="http://www.youtube.com/watch?v=UDtb8lePiys"]YouTube - Cal Poly Flight Motion Sim In-Action[/ame]


About your calculations - I'm getting 162.69Nm from 120 inch-lbs. according to trusty google:
http://www.google.ca/search?hl=en&sa...on+meters&meta=

Perhaps I am missing something in the equation though.

Dutchboy

The prices at surplus center aren't bad at all.
Had a look at the specs of the motors: If you want the 3 motors to carry the full weight of your platform, (say 120kg like mine) each motor would have to sustain 40kg. The torque of the motor says 120 inch-lbs which is 13.6Nm. with arm-length of 0.2m you would get 68N of force which can lift only 7kg. So it won't work for a non balanced platform.
If you use a big spring to offset the platform weight, it will still be critical, as depressing the spring also takes extra force. Seems that the torque of the motor is not sufficient (or maybe I made a mistake, I can only calculate in metric)
Just for reference: My homebuild actuators produce ~ 43N of force per Ampere. At 10 Amp, 430N gets a balanced 120kg platform really moving!
I use pulley / belt system for gearing as it can take lots of abuse. Standard gears don't like sudden reversal at high torque.

To avoid dissappointments, make sure you do these kind of calculations before you buy!

[Roland]

Keep in mind that the motor torque spec is in pounds-inch, not pounds-foot.
120 inch pounds = 13.55Nm
http://www.onlineconversion.com/torque.htm

[Dutchboy]

Of course! I missed that, thanks! I think I'm going to stick to low volt DC and my original balanced platform idea. Thanks for the help guys.

Dutchboy

Keep in mind that the motor torque spec is in pounds-inch, not pounds-foot.
120 inch pounds = 13.55Nm
http://www.onlineconversion.com/torque.htm