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i need to rotate a shaft of weight 1 kg. The shaft has to be rotated in the range from 1 to 150 r.p.m. load acting on the motor is almost constant during rotation (constant torque). It is very important that the motor has to rotate at all the speeds with in the range of speed mentioned. i.e if i mention the speed as 1 r.p.m the motor should rotate at 1 r.p.m, if 2 r.p.m is mentioned the motor has to rotate at that speed, like that from 1 to 150 r.p.m i need 150 equal increments of speeds(1,2,3.......6,7,........20,21,22,.........100,101.....150).

i calculated the torque with a high safety factor and a torque of 1kg .cm is sufficient.

what is to be done to fulfill these requirement, the complete specifications of motors are as fallows.

torque- 1kg-cm
operating or rated speed range or the output shaft speed required- 1 to 150 r.p.m
power supply line available - 230V AC
operating voltage of motor- 12V DC
power - 6W.

i searched for motors but reply is that it is not possible to get such a low speed, i am from mechanical background, so i don't have awareness regarding that. please help me

Gearmotors are the usual answer, I assume that you want a constant angular velocity. That leaves out steppers and even brushless servomoters as at 1 rpm they would be pretty lumpy. A synchronous AC motor could do it, but most aren't designed for speeds that low. Some torque motors could do it, but 1 rpm direct is pretty slow. Belt or gear reduction is the practical answer.

Regards

cww

In reply to Curt Wuollet: He wants to be able to control the speed in 1 rpm increments between 1 and 150 rpm. A "gearmotor" is typically just an AC motor with a gearbox. To get variable speed, you would need a drive. The straight forward answer is a small servo system with a gearbox. Most dealers who sell servos will sell a gearbox with it as part of a package.

The biggest problem would seem to be the 1 to 150 rpm speed range. If the system is equipped with a 20 : 1 gear reduction, then the servo motor will operate in the range of 20 to 3000 rpm. The question will be how smoothly the servo operates at 20 rpm. This will likely work, but the original poster should consult with a servo dealer about the best choice for the application.

Hi Michael,

May be a local terminology thing, but I have a plant full of DC gearmotors used with simple drives for the low speed conveyors etc. common in the printing industry. Many of them are so slow that they would probably work for him. Many drives regulate fairly well without a tachometer or encoder feedback. But, it he wants precise speeds, most digital servo setups can do that well, but they tend to be really spendy.

Regards
cww

You want a servo drive with a gear box. The servo drive and servo motor will give you a controlled speed. The gearbox will give you the speed reduction.

Hi,
Regardless of the method used to obtain the speed some measure of tolerance, velocity ripple, etc. needs to be specified. 1 rpm +/- how much?

BTW, with a direct motor application it may be more cost effective to explore analog sin/cos feedback devices as opposed to adding a gearhead or other reduction. Those feedback devices, after interpolation, can provide several million counts per rev. For closed-loop velocity control, this can be a huge benefit.

Your selection will be dictated in part by the level of precision needed at each end of the speed range as well as the level of ripple that is tolerable. From a ratiometric standpoint, controlling speed over a 150 to 1 range is a challenge.

Pulse width modulation for controlling the speed of a DC gearmotor is probably the least expensive combination. However, control over a 150:1 range may be a problem because of low speed stiction effects.

If the DC motor's optimal speed is 3000rpm and you wish to equate this to 150RPM, using a 20:1 gear reduction, stiction may occur at low range. At 1RPM, the motor would turn at a meager 20RPM. I think stiction in both the motor and gearbox would make this difficult to accurately control.

A step motor is a viable alternative - we use them in the speed range you are considering. A size 34 frame, 2 phase step motor will more than meet your torgue requirements even driving the load DIRECTLY. This would eliminate the cost of a gearbox.

Regarding ripple, the most common way to drive a step motor is what is called 'half-stepping'. This allows position control in increments of one four hundredth of a revolution (using a standard hybrid step motor).

However, postional resolution and ripple can be vastly improved by using a drive that has microstepping capability. This can improve resolution by a factor of 4, 8, 16, all the way to hundreds of times the base 400 steps per revolution.

Due to inductive effects, you cannot step the motor at many thousands of pulses per second, so to handle the wide speed range, you have 2 choices. Either use a half step drive to save money and 'suffer' ripple at low speed or use a microstepping drive that is able to DYNAMICALLY switch from half stepping to quarter stepping, eighth stepping, etc., etc.

I doubt you'll need it, but inertial damping would further suppess ripple and if you want it to be REALLY smooth, you can buy a step motor with more than 2 phases (beware, these are costly).

To review motors and drives, Google for companies such as Oriental motors, Shinano Kenshi, Sanyo Denki and NMB.

Your selection will be dictated in part by the level of precision needed at each end of the speed range as well as the level of ripple that is tolerable. From a ratiometric standpoint, controlling speed over a 150 to 1 range is a challenge.

Pulse width modulation for controlling the speed of a DC gearmotor is probably the least expensive combination. However, control over a 150:1 range may be a problem because of low speed stiction effects.

If the DC motor's optimal speed is 3000rpm and you wish to equate this to 150RPM, using a 20:1 gear reduction, stiction may occur at low range. At 1RPM, the motor would turn at a meager 20RPM. I think stiction in both the motor and gearbox would make this difficult to accurately control.

A step motor is a viable alternative - we use them in the speed range you are considering. A size 34 frame, 2 phase step motor will more than meet your torgue requirements even driving the load DIRECTLY. This would eliminate the cost of a gearbox.

Regarding ripple, the most common way to drive a step motor is what is called 'half-stepping'. This allows position control in increments of one four hundredth of a revolution (using a standard hybrid step motor).

However, postional resolution and ripple can be vastly improved by using a drive that has microstepping capability. This can improve resolution by a factor of 4, 8, 16, all the way to hundreds of times the base 400 steps per revolution.

Due to inductive effects, you cannot step the motor at many thousands of pulses per second, so to handle the wide speed range, you have 2 choices. Either use a half step drive to save money and 'suffer' ripple at low speed or use a microstepping drive that is able to DYNAMICALLY switch from half stepping to quarter stepping, eighth stepping, etc., etc.

I doubt you'll need it, but inertial damping would further suppess ripple and if you want it to be REALLY smooth, you can buy a step motor with more than 2 phases (beware, these are costly).

To review motors and drives, Google for companies such as Oriental motors, Shinano Kenshi, Sanyo Denki and NMB.

Hi,
Don't waste your time evaluating the numerous speed control techniques available without first defining the accuracy to which your speed must be controlled!

When you talk to a motion control device manufacturer they should - if they are being diligent - ask for such a spec so that they can evaluate if their technology is appropriate for your application.

Best Regards.