Stepper Motor - Electronic Circuits Projects Diagrams Free

netbug · 26th July 2006, 02:56 PM

Hi,

I am using an unipolar stepper from AstroSyn model SST0017. The specs of this stepper are 12 V / 0.4 A / 30 ohm. The holding torque is 2.4 Kg-cm and rotor inertia 27 g-cm2. This stepper is connected to a ULN2803, and it works fine. The only problem is that it gets very hot, as well as 7812 that is connected to it. Can I use some power resistors in series with the stepper to limit current ? Will this degrade torque ? Do you know another way to solve this ? This circuit will be closed in a wood box, so I don't want it to burn !!

Another drawback I found on this stepper, is that it is too much expensive for the project I am finishing. I would like to know, if anyone knows another brand of steppers, with similar specs but with a lower price ?

Best regards,

Pedro

hjames · 26th July 2006, 06:47 PM

If you want to reduce the temperature - add heatsinks and fans. Sealing anything in a wood box will cause it to overheat at some point. Now if you want to reduce the power going in, you can reduce the current going into the system by:

1) reducing the current/torque - (current and torque are proportional).
2) PWM the thing so that it isn't drawing so much power when it is idle.
3) using a better switch than the ULN2803 - this chip will have a ~1.5V drop when on, which means that the chip will be dissipating close to 2Watts and will probably need a heatsink.
4) !don't put the motor on a regulated power supply! What is the actual transformer voltage? The regulator is going to dissipate 0.8A * (voltage drop) which could easily be a few watts. Hook the motor up directly to the unregulated power supply and use a current limiting resistor to keep the current at .4A.

Dunno about Europe, but there are a lot of surplus steppers in that torque range for ~US$15. There are also a lot of import (ie made in China) ones as well that you can get from companies that sell motion control equipment.

James

netbug · 27th July 2006, 10:02 AM

Hi HJames,

Thank you for your reply. The idea of this project is to make a WatchWinder, so the circuit will be closed in a box. The stepper will rotate a wrist watch, to make it charged. I want to use a low consuming stepper, but otherwise a stepper that can't be stopped easily, that is if you apply some pressure with your fingers the stepper shouldn't stop.

The other goal of the project is to make a cheap watchwinder, so I must use a cheap driver like ULN2803, and I am looking for a cheap stepper that fits my project. Any suggestion for stepper specs that fits this project ?

Best regards,

Pedro Cardoso

hjames · 27th July 2006, 03:15 PM

This is for watches that are "charged" by being shaken?

I assume you don't need this thing to spin over a couple dozen RPM...

Don't even bother with a stepper. I'd suggest just getting a normal DC brushed motor with a worm-gear or other gearbox. Throw in a limit switch or optical sensor to determine how many rotations it's gone through. Is this a production product?

netbug · 27th July 2006, 04:20 PM

Hi,

Thanks again. This is for production. At beginning I thought it would be easier to count turns with a stepper, rather using a DC motor. Besides the stepper is very accurate and I can program it to run 1000, 1200 or 1500 turns per day. With a DC motor, speed increases with voltage, and the only way to count the turns will be, like you said, using a simple encoder. But will be this approach better to a product that intends to be produced ? Will this be cheaper ?

Well I think with a stepper I won't need a gearbox, because I can run it very very slowly. The main thing is that I need a simple and cheap solution, taking into account motor + driving IC.

Best regards,

Pedro Cardoso

hjames · 27th July 2006, 05:11 PM

Well, put it this way: where do you see stepper motors in (current) mass produced products? Printers .. and that's about it - steppers require more silicon to control, are more power hungry, don't inherently move smoothly - they will vibrate and make noise, and are inherently more expensive.

A DC motor that spins in one direction only needs 1 transistor to drive, and 1 sensor to sense velocity/position. Put the two in a feedback loop, and you can have a constant speed motor. As for actual pricing, I don't know your local suppliers, so I can't really comment...

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26th July 2006, 02:56 PM	(permalink)
netbug	Stepper Motor Hi, I am using an unipolar stepper from AstroSyn model SST0017. The specs of this stepper are 12 V / 0.4 A / 30 ohm. The holding torque is 2.4 Kg-cm and rotor inertia 27 g-cm2. This stepper is connected to a ULN2803, and it works fine. The only problem is that it gets very hot, as well as 7812 that is connected to it. Can I use some power resistors in series with the stepper to limit current ? Will this degrade torque ? Do you know another way to solve this ? This circuit will be closed in a wood box, so I don't want it to burn !! Another drawback I found on this stepper, is that it is too much expensive for the project I am finishing. I would like to know, if anyone knows another brand of steppers, with similar specs but with a lower price ? Best regards, Pedro

26th July 2006, 06:47 PM	(permalink)
hjames	If you want to reduce the temperature - add heatsinks and fans. Sealing anything in a wood box will cause it to overheat at some point. Now if you want to reduce the power going in, you can reduce the current going into the system by: 1) reducing the current/torque - (current and torque are proportional). 2) PWM the thing so that it isn't drawing so much power when it is idle. 3) using a better switch than the ULN2803 - this chip will have a ~1.5V drop when on, which means that the chip will be dissipating close to 2Watts and will probably need a heatsink. 4) !don't put the motor on a regulated power supply! What is the actual transformer voltage? The regulator is going to dissipate 0.8A * (voltage drop) which could easily be a few watts. Hook the motor up directly to the unregulated power supply and use a current limiting resistor to keep the current at .4A. Dunno about Europe, but there are a lot of surplus steppers in that torque range for ~US$15. There are also a lot of import (ie made in China) ones as well that you can get from companies that sell motion control equipment. James

27th July 2006, 10:02 AM	(permalink)
netbug	Hi HJames, Thank you for your reply. The idea of this project is to make a WatchWinder, so the circuit will be closed in a box. The stepper will rotate a wrist watch, to make it charged. I want to use a low consuming stepper, but otherwise a stepper that can't be stopped easily, that is if you apply some pressure with your fingers the stepper shouldn't stop. The other goal of the project is to make a cheap watchwinder, so I must use a cheap driver like ULN2803, and I am looking for a cheap stepper that fits my project. Any suggestion for stepper specs that fits this project ? Best regards, Pedro Cardoso

27th July 2006, 03:15 PM	(permalink)
hjames	This is for watches that are "charged" by being shaken? I assume you don't need this thing to spin over a couple dozen RPM... Don't even bother with a stepper. I'd suggest just getting a normal DC brushed motor with a worm-gear or other gearbox. Throw in a limit switch or optical sensor to determine how many rotations it's gone through. Is this a production product?

27th July 2006, 04:20 PM	(permalink)
netbug	Hi, Thanks again. This is for production. At beginning I thought it would be easier to count turns with a stepper, rather using a DC motor. Besides the stepper is very accurate and I can program it to run 1000, 1200 or 1500 turns per day. With a DC motor, speed increases with voltage, and the only way to count the turns will be, like you said, using a simple encoder. But will be this approach better to a product that intends to be produced ? Will this be cheaper ? Well I think with a stepper I won't need a gearbox, because I can run it very very slowly. The main thing is that I need a simple and cheap solution, taking into account motor + driving IC. Best regards, Pedro Cardoso

27th July 2006, 05:11 PM	(permalink)
hjames	Well, put it this way: where do you see stepper motors in (current) mass produced products? Printers .. and that's about it - steppers require more silicon to control, are more power hungry, don't inherently move smoothly - they will vibrate and make noise, and are inherently more expensive. A DC motor that spins in one direction only needs 1 transistor to drive, and 1 sensor to sense velocity/position. Put the two in a feedback loop, and you can have a constant speed motor. As for actual pricing, I don't know your local suppliers, so I can't really comment...