This is my first post and I am quite new to Arduino.
I am selecting a stepper motor to power a window opening mechanism and have some questions that I have not been able to solve despite quite lengthy online searches.. I would be very grateful here if someone could clarify!
If there are two motors that have similar torque but one is low voltage and the other is high voltage what are the relative benefits between the two?
I understand that when Steppers are stationary is when they consume the most energy... Given that the window opening mechanism will be stationary most of the time this is a concern. Are there any stepper motors available that use some kind of physical lock to prevent this constant consumption of current?
What is the best way to power my stepper to prevent overheating? I was thinking that I could have a stepper motor with a higher torque than what I need and run it at a low current (providing the torque that i actually need) so that it never gets too hot.
My intention is to leave the system running at all times. Is the stepper motor the best choice for this kind of application?
Have a look at Stepper Motor Basics. I hope it will answer most of your questions.
Stepper motors naturally run hot - uncomfortable to touch.
Lower voltage motors normally take a higher current and are generally easier to drive at higher speeds. The current is the important thing.
I suspect a DC motor with a gear drive would be much more suitable for your application. You are unlikely to need the precision that a stepper motor provides. A worm drive will prevent any motion when the motor is unpowered. However that would also prevent the window being opened manually in an emergency - if that is necessary. There might be enough friction in a non-worm gear train to prevent normal movement without preventing emergency movement.
Whether you use a DC motor or a stepper you will need at least one limit switch to identify when the window is fully closed. Another switch to detect when it is fully open would probably be essential with a geared DC motor.
I think I will need the precision.. This is for a greenhouse and I want to open the window by set increments in order to control the temperature.
So a person using a low voltage high current stepper wants his motor to do something that requires high speed... not my case. So I would be better with a high voltage low current stepper?
Lets say I am using the 12v 0.35A 2kg*cm Nema... I have an adaptor that supplies 12V 0.33A and I can set my driver to limit the current to 0.33A
Does this mean that my motor will run cooler suffering a loss of torque?
As I plan to leave the motor on at all times the temperature which it runs at is pretty key to the longevity of the system. I dont mind if I lose a bit of torque but still have enough to perform the function.
willacker:
Lets say I am using the 12v 0.35A 2kg*cm Nema... I have an adaptor that supplies 12V 0.33A and I can set my driver to limit the current to 0.33A
This is a bit confusing. The current limit should be applied by the stepper driver board. The power supply should not attempt to apply a limit.
I don't know anything about the longevity of stepper motors. It does seem logical that a high torque motor run at lower current would run cooler. But whether it saves any energy (compared to a motor with just the required torque) is a separate matter.
How does the window work? Is it hinged or sliding?
I presume, as it is a greenhouse, that emergency egress is not a requirement.
You could use a stepper to drive a screwed rod. That would allow you to depower the stepper without any movement occurring. Your Arduino would need to run continuously to remember the step count.
You can also get rotary encoders that allow you to get an accurate indication of the rotation of a DC motor. But they are a bit more complex to program for.
OK. The stepper driver board regulates the current.. But I assume that if the current being regulated comes in at close to what it is meant to be that makes things easier for the driver right?
I guess I'll need to buy a high torque and a required torque motor and do some experimenting and see which works better.
Hinged.. the motor pushes the bottom of the glass and the top is held by hinges. pinion carries the pane of glass up and away.
Thats an interesting suggestion about the screwed rod! I will def look into that.... i may leave the rotary encoder until i am more advanced.. I am pretty much at my limit right now! haha
willacker:
OK. The stepper driver board regulates the current.. But I assume that if the current being regulated comes in at close to what it is meant to be that makes things easier for the driver right?
No. Quite the opposite I suspect.
If the power supply is near its limit the voltage will drop and just confuse everything.
Having excess amps available never causes a problem.
There are many instances of the use of wiper motors attached to a hobby servo to provide an inexpensive, powerful drive that will hold a position when no power is applied. A search using 'wiper motor servo' will turn up explanations, examples. - Scotty