Choosing the best motor for this specific project.

Hey everyone!

I'm doing a project that has to do with parabolic trough collectors. And my task is making the tracking system on one axis for this project. I made some simple one axis solar trackers using servos and stepper motors on a small scale to get accustomed to using the arduino and the C++ language (I know some programming in python and bash and took an electrical engineering circuits lab so that wasn't too hard), however now I want to make a solar tracking system that can carry something like a 5 N-m torque. The project looks something like this:

What I'm looking for basically is a servo/stepper/DC motor that can provide a 5 N-m torque when it has a pulley or a sprocket attached to its shaft and then that sprocket has a chain that is linked to the steel chains at the two sides of the parabolic trough collector. I've read around a lot on the internet that, when faced with these mechanical loads, the motors that can carry these loads sometimes need special control modules and the arduino won't work. I'm afraid of choosing a motor that won't work with the arduino. [Budget is around 500$]

Would a Nema 23 stepper motor be able to carry the load? Or should I go for those large servos or DC [jack] motors? Any help in that regard is appreciated!

Depends which Nema23 motor.
There are many, all with differing holding torque.
Usual for them to display this in oz/inch or kg/cm but easy enough to transpose into nm.
Probably need a good hefty voltage to give the rated output.
If you are gearing down to the motor then this will have to be taken into account as it will be a mechanical advantage all-be-it slower speed.(to some degree)

Screw jack motor drive has the added advantage of high reduction and (@ more then 40 degree thread pitch) load will not turn the motor, so if stepper or dc motor, it can be completely turned off when new position is reached.

bluejets:
Depends which Nema23 motor.
There are many, all with differing holding torque.
Usual for them to display this in oz/inch or kg/cm but easy enough to transpose into nm.
Probably need a good hefty voltage to give the rated output.
If you are gearing down to the motor then this will have to be taken into account as it will be a mechanical advantage all-be-it slower speed.(to some degree)

Screw jack motor drive has the added advantage of high reduction and (@ more then 40 degree thread pitch) load will not turn the motor, so if stepper or dc motor, it can be completely turned off when new position is reached.

Yeah you’re right, just looked up some catalogues of some NEMA 23 motors, and they have a ton of different specs, I even saw some of them that can provide 3 N-m of torque, although none of them come close to 4 N-m unfortunately. I may have to look at Servos or DC Motors in that case, hopefully I’ll something that actually has a shaft that can have a pulley mounted on it.

Your comments about screw jack motors is differently important and I will take that into consideration!

Stepper motors are very inefficient and will probably use more energy than the sun provides.

A geared DC motor is almost certainly a better choice. If it uses a worm reduction gear it will hold position without any power.

...R

Stepper with worm drive or positioning screw can also be used very efficiently as you can switch it off, like the DC motor. Control is easier, you can just tell it to do n steps. In case of a DC motor you have to read an encoder to know how much it moved.

Note that your stepper (or other motor) does not necessarily have to delivery 5 Nm by itself. If it's geared down 10x, the torque goes up 10x, so a 0.5 Nm motor can delivery 5 Nm torque that way. It's just slower, but especially in case of a DC motor that's a very good thing. Those things tend to run best at speeds of 10-20k rpm.

I suggest to consider using a linear actuator to set the collector angle.

They use no power unless moving, are quite powerful and have extremely high static "holding power". Get them from several sellers, or, as videos available on line show, they can be made very cheaply using threaded rod, a traveling nut and a motor from a "thrift store" battery operated drill.

Robin2:
Stepper motors are very inefficient and will probably use more energy than the sun provides.

A geared DC motor is almost certainly a better choice. If it uses a worm reduction gear it will hold position without any power.

...R

Although the amount of energy consumed is not a concern in this case, use of energy efficient solutions is a great plus for the project. Guess I'll look more into DC motors.

wvmarle:
Stepper with worm drive or positioning screw can also be used very efficiently as you can switch it off, like the DC motor. Control is easier, you can just tell it to do n steps. In case of a DC motor you have to read an encoder to know how much it moved.

Note that your stepper (or other motor) does not necessarily have to delivery 5 Nm by itself. If it's geared down 10x, the torque goes up 10x, so a 0.5 Nm motor can delivery 5 Nm torque that way. It's just slower, but especially in case of a DC motor that's a very good thing. Those things tend to run best at speeds of 10-20k rpm.

So you're saying if I buy a certain DC motor that is capable of a certain torque output, and I "gear it up", I can achieve the desired torque? Do I have to go to a machinist to increase the torque output with gears or are there manufactured solutions for this?

jremington:
I suggest using a linear actuator to set the collector angle.

They use no power unless moving, are quite powerful and have extremely high static "holding power". Get them from several sellers, or, as videos available on line show, they can be made very cheaply using threaded rod, a traveling nut and a motor from a "thrift store" battery operated drill.

That's what I saw everyone who ever did a tracking system do for parabolic trough collectors, the issue here is how to attach these linear actuators to the PTC we have and hold those actuators in place, since we made that underwhelming structure that is carrying the PTC.

Adrammelech:
So you're saying if I buy a certain DC motor that is capable of a certain torque output, and I "gear it up",

The usual thing is to gear DOWN so the output shaft runs more slowly than the motor. If you gear down by (say) a factor of 25 then the torque will be multiplied by 25 (in theory - it won't be that much due to friction).

You can buy motors with gearboxes attached. The Pololu website has several but you can get similar things (and much more powerful devices) elsewhere.

I don't think you have told us how your Arduino will determine when the reflector is pointing in the correct direction.

If you want to turn it to a specific angle a stepper motor (with worm reduction gear) would probably be a convenient arrangement. However if you de-power a stepper motor there is a risk that you miss steps, but for your project the error may be so small that it does not matter.

If you are using the energy output or the brightness of the sun for position feedback then I reckon a geared DC motor would be fine - just move a little and see if there is an improvement etc etc.

...R

the issue here is how to attach these linear actuators to the PTC we have and hold those actuators in place, since we made that underwhelming structure that is carrying the PTC.

If the structure is "underwhelming", keep in mind that it WILL be destroyed by high winds. Which is, incidentally, another reason to consider a sturdy actuator or drive mechanism.

Adrammelech:
Yeah you're right, just looked up some catalogues of some NEMA 23 motors, and they have a ton of different specs, I even saw some of them that can provide 3 N-m of torque, although none of them come close to 4 N-m unfortunately. I may have to look at Servos or DC Motors in that case, hopefully I'll something that actually has a shaft that can have a pulley mounted on it.

Your comments about screw jack motors is differently important and I will take that into consideration!

You seem to have missed the point that using a gear reduction will reduce the high motor torque requirement by the factor of the ratio.

For a fun way, use empty container and counterweight. Fill the container up with water to rotate the lens during the day.

You have a pump and a water supply already in place, just need a valve to divert as needed.