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Torque Motor Selection

Torque Motor Selection

Torque Motor Selection

(OP)
I am looking to get a DC motor that I am going to be using to provide force feedback to a flight simulator flight stick.  The motor is going to have a very limited range of motion, and be used only to create forces without rotating.  I need a motor that is able to generate controllable forces between 0 and 140 lbs to get the desired stick forces.  I have been looking for torque motors, but have been unable to find any that will work.  My question is if I am using the right approach by selecting torque motors, and if so, does anyone have any ideas where I could find something that will work?  I am pretty new to motor control stuff, and was wondering if I need a torque motor at all.  Would a different type of motor do the trick better?  I was unsure if it would be bad on the motor to not allow it to spin, and force it in the opposite direction it is trying to spin, as will happen w/ my system.  Any suggestions will be greatly appreciated.

Thanks.

RE: Torque Motor Selection

Torque motors as I know them are used to provide a constant torque on something like a takeup reel. The torque is constant.
Try a fan cooled DC motor and vary the rotor voltage. The torque will vary.
respectfully

RE: Torque Motor Selection

(OP)
I was under the impression that with DC motors torque changes with current, and speed changes w/ voltage.  I also thought that electrical power steering systems in some cars generate forces with torque motors.  Would it be too much wear on a DC motor to force in in the wrong direction, or hold it in a continuous stall state?  Would a cooling fan be enough to fix this problem?
Thanks

RE: Torque Motor Selection

At stall, current is proportional to voltage. As the speed rises the back EMF rises and the current drops. How much torque do you want? How much travel? How fast must the response be?
You can stall a DC motor and you can force it backwards. Cooling and brushes are the issues. You may have to use forced cooling from an external fan. You may have to experiment with different grades of brushes for best performance at a standstill.
You can use a spring. A motor driven screw-jack can compress the spring and vary the force.
I haven't seen electric power steering, but i haven't seen everything.
I am familiar with back-up steering systems used on front-end loaders and log skidders and forwarders. These units have hydraulic steering. No hydraulic pressure, no steering. The steering pressure pump is a fairly large hydraulic pump driven off the engine. It is actually large enough to stall the engine at slow speeds and part throttle.
Some jurisdictions mandate an electric backup pump to maintain some steering ability in the event of engine failure. This feature may be found in mountainous regions.
This is not what you are looking for.
How about hydraulic positioners. You can use the positioner to compress a spring and so convert linear movement into torque or force.

RE: Torque Motor Selection

(OP)
I am looking at having around 110 lbs inchs of torque with less than 90 degrees travel.  I'm going to connect the motor to the base of the stick so I need quite a bit more force than I wish to generate where the pilot feels it. The response is going to have to be small as I think anything over a few milliseconds would be noticable to a pilot.  In regard to hydraulics, I'm wanting to use DC motors instead.

RE: Torque Motor Selection

Nice research, Clyde38.
LPS for you.
respectfully

RE: Torque Motor Selection

(OP)
Thanks for the idea, but I already have tried Aeroflex, and searched for other limited angle torque motors, but have been unable to find anything powerful enough.  If you guys think a DC motor will do the trick, I think I'm gonna try and go that route.  I think it will be alot easier to find the forces I need, and find a controller and driver for it also that can interface w/ a PC as I need.  Does anyone know of any good places to search for motors and controllers that I could use?
Thanks.
Richard

RE: Torque Motor Selection

Using a DC motor as a torque motor at low speeds involves mainly two issues.  First, the motor has to be able to cool itself without shaft rotation.  Second, the current at low speed or stall must not be so high as to overheat the commutator bars and cause comm distortion.

The first issue is usually dealt with thru an auxiliary blower or, in small sizes, by oversizing the motor frame.  The second issue is usually dealt with by using a larger motor and not exciting the armature fully thus keeping the commutator currents well below design levels.

Good luck!

RE: Torque Motor Selection

If by "DC Motor" you mean a brush commutated motor, I believe that you are going to have trouble.  Because of temperature etc. and the commutation system.  Try a brushless "DC" solution.

http://www.polysci.com/Motors/torquembrshless.html

RE: Torque Motor Selection

First, why not use just spring/s?
For a motor to simulate a resistance torque (not a force) it has to be at least 10 times faster response time than the force rate or change on the stick. There is always a time delay for the current to build inside the motor coil and produce the resistance torque. Therefore, the motor coil resistance and inductance should be as small as possible and the voltage as high as possible. This will result in a current limiter circuit, and a very high voltage drive a sophisticated feedback control system. Only mechanical spring will respond instantly without any delay.

From the height of my 30 years of experience it amazes me that from time to time engineers come with this inventive idea to simulate resistance using a motor without paying attention to the instant response time needed and its implications on the size of the motor the voltage and current needed to try to achieve what a simple spring will do.

RE: Torque Motor Selection

(OP)
I was planning on using a brushless approach.  I will look more closely at those two torque motor companies.  In regard to springs, that approach is too simplistic for this project.  I need an adaptive system that can create precise forces based on different speed, attack angles, etc. that create different forces on the control surfaces of the plane.  We are building a full motion simulator, so using springs to generate a constant force on the stick will not be appropriate.  In addition, the trim tabs will be easier to implement with electric motors versus springs.

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