Motor control

Perhaps:

Not enough information. You talking about a table top=20 fountain, or something on a bulldozer scale or larger?

Forget hydraulics. Just place a 1 ton rock on it. it will=20 produce a ton of force with no horsepower, at all.

Seriously, power involves both force and velocity. You have=20 only half the puzzle.

What about motor failure with arcing windings. If the=20 atmosphere is flammable, you need stuff rated to operate=20 (and fail) in that environment.

If you include a mechanism for position feedback, you can=20 get pretty arbitrary accuracy from any prime mover.

What is the cost of having the position wrong? Open loop=20 methods include the possibility of being wrong without the=20 control system being aware of that fact.

At the moment, I think you are worrying about the color of=20 paint on the motor (so to speak) before you have got a good=20 hold of the more important system requirements. I suggest=20 you work on a better definition of the physical requirements=20 of your ideal system and then see how far you have to back=20 down from that ideal to find practical hardware. Start out=20 with the physical movements (masses, forces, distances,=20 velocities, accelerations) you want to produce, and work=20 back towards the prime mover. This will reduce the number=20 of times you have to start over.

--=20 Regards,

John Popelish

Dangit John, you said just about everything I would have.

Except that there is no reason that a motor with feedback has to be controlled by an analog circuit -- a microprocessor sitting in between and ADC and a DAC is pretty much the way to go these days. If what you're building is even moderately low production then you want to buy someone's motor control box and bolt it onto your equipment someplace.

The OP should probably also get someone experienced with designing for explosive environments in on the project earlier rather than later, at least to consult on the safety bits. And that's not just for regulatory approval -- things that go BOOM can cost lots of money if not lives.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote in news:QrCdnWrJxKrOeMbVnZ2dnUVZ snipped-for-privacy@web-ster.com:

There are some microcontrollers that are better than others for the job, obviously. I'd pick one that handles the quad encoder in hardware, like the 18fx331 line. Makes life easy. The output is PWM, so no DAC or ADC!

--
Scott
Reverse name to reply

What is the motor being used for? Is the motor being used to drive a pump to pump a hydraulic fluid?

Does this mean you are using a piston to produce 1 ton of force? The force produce by a piston is proportional to the area of the piston times the differential pressure applies to the piston. Hence you could generate one ton of force with either a large piston and a small differential pressure or a small piston and a large differential pressure. The amount of fluid to move the piston is proportional to the area of the piston times the velocity of the piston. Hence there is a definite advantage to going to a higher differential pressure to reduce your hydraulic flow requirements. From what you have told us you could use an accumulator and a small hydraulic pump to meet your requirements.

If you really are using a hydraulic piston to create a one ton force you could install your pump outside your potentially flammable environment. Inside your hostile environment would be your piston, a servo valve, an accumulator, a position sensor and operator controls. The hydraulic pump and servo amplifier would be installed in a non hostile environment.

Yes you can easily obtain +/- a few cm control accuracy with a hydraulic control system.

Howard

I was going to suggest a bottle jack. I can lift a ton with one of these and my thumb.

The OP will have to characterize the environment. What sort of vapor/dust/etc. makes it explosive? From that point on, there are sealed motors and device enclosures to suit almost anything. If you have the money.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Disclaimer - These opiini^H^H damn! ^H^H ^Q ^[ .... :w  :q  :wq  :wq! ^d
exit X Q  ^C ^? :quitbye  CtrlAltDel ~~q  :~q  logout  save/quit :!QUIT
^[zz ^[ZZZZZZ ^H  man vi ^@  ^L  ^[c  ^# ^E ^X ^I ^T ? help  helpquit ^D
man quit ^C ^c  ?Quit ?q CtrlShftDel "Hey, what does this button d..."

First you need to learn about hydraulics.

Thanks all for your input,

I think I need some basic lessons in mechanics and hydraulics, before I can proceed.

What I need is for someone to describe how to get from mechanical energy to electrical energy and give me an example calculation.

Say you have one tonne (1000kg) moving at 1meter/sec constant velocity (no acceleration). How much power would it take in watts to keep the mass moving at this speed?

Is that enough information?

I assume that different mechanical mechanisms like gears, pistons affect the speed that the energy is transferred and don=92t drastically effect energy throughput (assuming high efficiencies), is this correct?

I told you I didn=92t know much about mechanics.

Reggie.

Answer is 9.8 kilowatts

Answer obtained from

Enter your quantity in top line, select kilograms meters/sec in left column, select kilowatts in right column and answer appears in bottom line.

al

ect

t

but

a

ou

do

p r . y

Thanks hrh for the convertion site.

Now is this statment true?

I assume that different mechanical mechanisms like gears, pistons affect the speed that the energy is transferred and don=92t drastically effect energy throughput (assuming high efficiencies), is this correct?

So would I need a 9.8KW say 10KW motor to move this mass at this speed?

Yup.

...or you could read a high school Physics text. Now would be a good time to stop expecting people to spoon-feed you the answers and bone up on the basics.

Classical Mechanics says ZERO. "An object in motion STAYS in motion UNLESS ACTED ON BY AN EXTERNAL FORCE." You need to quantify **all** the variables.

Nope.

ical

rrect

a

put

, but

g a

you

r do

oop

d

for

s).

f

my

y

ly

What are you doing with the mass? If you are trying to lift the mass straight up then the answer is yes. Gravity is applying an opposing force to the mass. But if your mass was mounted on wheels or sliding on a low friction surface and you were moving the mass in the horizontal direction then the answer is no.

Howard

. .

. .

The only force needed is that which overcomes friction. So, in a frictionless environment, you don't need any force to keep the mass moving. If you want to accelerate the mass, that's a different story.

Have a look at this:

's_laws_of_motion

--
John B

Zero, if you ignore friction: "I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." --

Hope This Helps! Rich

What about gravity?

Howard

Gravity like electric, and magnetic fields is a conservative field, until you take into account some relativistic issues, for any of them.

If he'd meant "lifting", howcome he didn't say, "lifting"? ;-)

Thanks, Rich