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docel
04-13-2006, 07:28 PM
HELLO!
It is Very amusing to see Engineers 'misusing' stepper motors. Is this because they are 'cheap' or is it because your guides tell you to use them.
There is such a thing as design parameters and the proffessional has to pick and choose the right component for the right job, after considering all the component characteristics.
Most of the users do so because it is " fashionable" , to show-off.

If I were an examiner, and I saw a misused Stepper motor, I would certainly cut marks for wrong application.

prani
04-15-2006, 02:36 PM
I read ur article on the misuse of stepper motors..What exactly do u use them for..?Are they of use in a simple robotics project...Like for instance..a robot used to collect balls..or something of that sort..?

docel
04-16-2006, 04:48 AM
hi prani,

:arrow: Stepper motors are used basically for position control. They rotate in steps of 1.8, 3.6, 7.5 or 15 degrees. The drive for the motors are pulses in a particular pattern and needs some circuit with or without a microcontroller and programming. It consumes more current, even when it is static It is a low speed motor: the torque is more at low speeds and decreass as the speed increases. The advantage is that no feedback is needed to determine position as the count of the drive pulses can indicate the position. This does not work if the motor stops inbetween (missed pulse). Then the positional information is lost. They are very heavy proportional to the current , torque and step size. The starting torque is low.

The stepper motor should not be used to move a load. A new stepper motor is VERY expensive. The popularity is due to the junk Hard-disk Steppers (12V) available on the foot path. These drives are more than 15 years old and are obsolete. These junk steppers are no longer available as even the junk is exhausted. The present cheap junk steppers are 24VDC and come out of PC Printers. They hardly work @12v.
The cost of a stepper motor+ the drive circuit+ the disadvantages is less than the cost of a reduction gear DC motor.

:arrow: DC motors rotate continuously (smooth), are low current , high speed devices but need external feedback devices for position prediction (Encoders, chopper/light interrupter wheel with LED/Photodiode combo, Magnetic pulse generator, Cam driven mechanical switch etc.,). A reduction gearbox must be used for low speed applications. This will also multiply the torque(Load moving capacity, "strength".).
DC motors are meant to carry/ move loads, but needs a reduction gear for appropriate speeds and feedback for position. The torque can be increased along with speed using PWM drive. A simple timer IC 555 can be used for both feedback and PWM. The starting torque is very high.

:!: Steppers are basically use in college labs as demo/excercise of software programming via the obsolete 8085 kit. This is because the drive interface and the bulky stepper motors are part of the 8085 kit, and the software is also supplied by the manufacturer of the kit. :!:

vikas
04-16-2006, 10:53 PM
Totally agree with you docel ... why the facination with steppers . There are uses for them but they way they are used is just plain stupid ... mostly overkill for simple jobs.

nmittal
04-18-2006, 02:55 PM
Hi,
I saw very cheap geared DC motors in mumbai at servo, the original motor is from some company Kopal. The best part is that these motors have an in built arrangement for feedback. So not external feedback is required

docel
04-18-2006, 07:58 PM
hi mittal,
Well adding a magnet and Hall-effect sensor is not difficult, You can make a simple encoder wheel and devise a led / P. diode combo for the sensor. No need for the rare and expensive 'Reflective Sensor'.

Also, Robonence has a 60RPM/. 4kg cm/ 12VDC gearhead for abt. 200/- with a built-in tacho generator (Magnetic).

This is, in many ways, cheaper and more elegant than the Stepper!!
And with the torque, will beat any type of Stepper for any purpose...lying down :!: :!:

:arrow: ..and Where is the Kopal Servo/ and what was the cost??

Beanie
06-23-2006, 01:26 AM
hi...
well i would think that stepper motors are easier to control rather than their DC motors, and if u need to measure the distance traveeled, its more acccurately measured if we are using a stepper motor. Morever, the extra circuitry, for reversing, speed control etc. can be avoided while using stepper motors. Of course, for a simple robot, it wil be too much of a headache to go into the details of a stepper motor when u can use a simple DC motor instead, but if u fall into a habbit of working with steppers, you wont be able to think anything else except the STEPPERS....

Best of Luck

docel
06-23-2006, 01:56 AM
Supposing it stops- where is the accuracy/ distance measurement then???

Beanie
06-23-2006, 11:08 AM
hi....

but it never stopped working for me..one will have some problems initailly with the dteper motors, but once he knows how to work with it, its pretty simple....

Geared DC motors are easier to handle for a beginner, there's no second opinion to that...

Ttake care

subot_robot
07-15-2006, 08:33 PM
Servo motors are good alternative to stepper motor. They consume less current deliver more torque and are very light and small. It is possible to control position accurately by giving suitable pwm signal. But they are expensive and not available or not easily available in India. I will be really happy if good servos at competant price(like fatuba, hitec) are available in India.