Best way to power a small Nema 17 0.7Amp 12v and make ir portable

Hi!

I'm currently working on a Barn Door Star Tracker project. It basically is an Arduino controlling a stepper motor that will rotate at 1.09 RPM

After doing some research I decided to use a small Nema 17 motor that needs 12v and 0.7 Amp (model 17HS4023). I think it is strong enough to move my 4 pound camera and lens.

However it seems very weird to me that some people power a nema motor with the 5v pin from an Arduino and it seems to work :thinking: Anyway, I would like to power my project the right way, that's why I'm thinking about using a XL6009 DC-DC 10W 3A Boost converter to boost 5v to 12v and power the stepper motor properly.

Here is where I need help. Would a 5v 2.0A usb output from a power bank be enough to power the Arduino and the Boost converter in the way I described?
Would it be a better idea to power it with rechargeable AA batteries?
Would a 16850 Li-Ion and this shield be good enough for this job?

I would like to run it for +/- 3 hours and the project might be operated in freezing conditions (Lowest temp would be -10 Celsius / 14 Fahrenheit)

Thanks in advance for all your help! :grinning:

What torque is needed to move the camera and how will it be moved? And what are you intending to use as a stepper motor controller?
As far as powering the project, do the math. Volts X amps X time = power needed from the source. Probably double that to be safe.
By the way, NEMA refers only to the size of the mounting of the motor, nothing else.
Paul

Thanks for answering Paul!
In order to drive the motor I have to options, either the DRV8825 or the A4988 boards. I have them both.

The motor I described has a torque of 14 N.cm and it will have a 10 teeth gear that will rotate a 42 teeth gear, something like this:
Screen Shot 2021-11-23 at 2.28.25 p.m.

Where is the camera attached?

This is how the project should look at the end and how the camera would be attached:

If the motor is not strong enough to move my camera I rather use a smaller camera than a bigger Nema motor (because it will need more power and a bigger/more complex power setup)

You have some interesting ides most should be good.

Start with your buck/boost converter (SEPIC). I use them a lot so lets determine what it is going to need to power your motor at full load without any extra for starting etc. The data sheet states β€œThe module also offers a very high conversion efficiency of less than 94% with a 0.5% load regulation. So lets do some simple calculations. I will round the 94% to 85% efficiency, just to be safe.

Start by multiplying the 5V times the efficiency and you get 4.25 (use as a pseudo voltage) We take our target voltage 12V and divide it by your pseudo voltage of 4.25V and get a ratio of about: 2.83. Now multiply your motor current 0.7A times 2.83 and you get about 2 amps. This is what the batteries will have to supply without any additional for stall, overload, etc. Your converter should be adequate.

First many people do things with Arduinos they should not, That does not make it OK. Many times we hear it worked just fine then quit days, weeks etc later. Many times it is they did not follow the rule β€œA power supply the Arduino is NOT!”.

Lets use 100mA for the Arduino current requirement, there are many varieties and this should be safe. At this point you need 2.1 amps for the Arduino and motor or 2.1 amp hours of power per hour or 6.3 for 3 hours.

The next thing I suggest is putting the motor in a freezer and see what power the requirements are at the colder temperatures. At this point you should be able to determine what you need and please let us know what you decided to do.

I see it, but I don't know what I am looking at. I see a tripod and something mounted on it. I see what may be a camera. I see your gear set, but what is the curved thing?

The curved thing is a threaded rod that supports the camera. The stepper motor will make the gears rotate so the camera can lift :slightly_smiling_face:

The goal of moving the camera that way is to compensate the earth's rotation movement so I can take a long (minutes long) exposure of the starts and other celestial bodies at night.

Something like this video: Barn Door Startracker DIY - YouTube

The 0.7A are the current for each coil, so you have to multiply by 2 to get the total current the motor needs. If you don't need the full torque you may reduce the current to save power.

This motor and the drivers (DRV8825/A4988) don't really fit together. These drivers are current drivers and they need a much higher voltage than the rated motor voltage to work properly.
This motor is more intended to be controlled via a simple H-bridge.

So something like this MX1508 H bridge would be better to control the motor?

If the motor is not strong enough to move my camera I rather use a smaller camera than a bigger Nema motor

If speed is not a priority, just increase the gear ratio, then you can maybe use a pancake stepper.

Not really. Look at the specs:

  • Module supply Voltage: 2-10V DC
  • Voltage output: 1.8-7V DC

Thanks for all your help!

This is a very interesting but kind of complex project, In order to make it work you have to know something about astronomy, photography, basic coding, electronics, maths...

There is no step by step guide to make a barn door tracker so im trying to figure it one subject a the time.

Once I figure it all I'll make a guide in instructables.com :wink:

The maximum speed would be 1.09 RPM or so. By pancake motor you mean the 28BYJ-48 5v stepper motor?

I have seen some people using it for this project. Some say it is strong enough and some other say that it is not strong enough for a camera with a big telephoto lens. That why I think the Nema 17 17HS4023 might be a better option for me.

You are right, the MX1508 won't be good enough.

I found this L9110 2-CHANNEL MOTOR DRIVER it is rated for 12v and 0.8 A for each coil.

You have NEMA 17 motors that are just a bit smaller.
checkout the 17hs0401-18b

Well, and that one can be used with your current drivers :wink:

You cannot have a curved threaded rod because the thread pitch must be a constant and the curve makes the pitch vary from small on the inside of the curve to large on the outside of the curve.
Suggest you pivot the entire motor and gear assembly. Looks like you have the hub of the big gear threaded to match the threaded rod.
If so, use a metal threaded rod and match it's thread with the hub of the big gear. Then as the angle of the threaded rod changes, the entire drive assembly will follow it.
With your elegant design, then, then ONLY torque needed is that needed to overcome the friction of the threaded rod/main gear. So, a very small DC motor could easily drive the whole assembly.
Paul

Yep, the rod is metal and its pitch is 0.8. Originally it is a M5 straight rod but I bended by hand to perfectly match the circumference of a 20cm radius circle (well almost half of it). The big gear is designed to have on its hub an M5 nut and that's how it moves the camera and the upper part of the "hinge". The rod has to be bended that way because if I leave it straight the whole project will have "tangent error" and it will not longer track the stars for a long period of time.

I'll try to do what @gilshultz suggests and see how it works, for how long and if I can decrease the amps delivered to the stepper motor to make it work for longer but still moving the camera.

Once I put everything together I'll share the results in this thread :slight_smile:

BUT, it is NOT M5 after you bent it!!!!