Need help choosing motor and power supply

Hey guys!

I am building a small project using an Arduino Micro. In the project, I need to control a DC Motor's speed through my Arduino's PWM port. It's extremely important that the motor runs at a constant speed of 60 RPM.

Because of this requirement, I am a little confuse on what power source and type of motor to use. I initially though about using 4 AA batteries and a 3.3v - 6v micro motor, but I am not really confident that the motor will keep its RPM constant while the battery runs out and the voltage drops. And since I don't have experience with electronics, I am really confuse with choosing the right motor for the right power supply.

Could someone point me to the right direction? Do you guys think I shouldn't use batteries?

Thank you all for your help!
Marco Paiva

I would help to know what the motor is actualy used for. What do you mean by a constant speed of 60 RPM: 60±1 RPM, 60± 0.01RPM. What kind of load is on the motor? If it is constant, it is not too hard to keep it at a constant revolution (with maybe some kind of flywheel). If the load is not constant, then you will need some feedback (a rotary encoder). You talk about a micromotor. Will it be the size you use on small drones or the ones sold by Pollolu (about the size of a thumb).

The Micro can be powered with a 9V battery. The digital pins will output a constant 5V, but they will only supply 20mA. You are garanteed that the power on that pin will be at 5V, unless the battery's power goes below 7V. You will have to see if that is enough current for your application.

If you intend to use external power, it has to be regulated. There are many options to do this.

Help us help you by better describing your project.

Thanks for the reply, jbellavance!

Sorry, I should have been more specific about the project. I am building a small electric zoetrope.

The motor will be used to spin a small 3D printed disk (60mm in diameter and 5mm in height). The disk will be the only load, and judging by its size, it won't weight more than 50 grams.
The motor needs to fully rotate the disk 60 times peer minute (1 full rotation peer second).

I don't have a lot of footprint to work with. The circuit and motor must be in a 70mm x 70mm x 60mm enclosure. That's way I thought about a micromotor. But since I don't have a lot of experience with it, I am not sure if micromotors are even the best option for this project.

From what I understand, I can't really power a motor through Arduino's digital pins because of the motor current will, most likely exceed the what the Arduino can supply, right?

Hi,

First, you can't get a plain micromotor to run as slow as 1 revolution per second. You will need some motor with a gear reduction or a small stepper motor.

How "Smooth" must the movement be? If it had 200 or 100 steps per revolution would that work?

terryking228, you are right! It would have to be a geared motor. It doesn't need to be a micromotor, though. Although, I though I could use PWM to slow down the motors speed to about 1 revolution per second.

terryking228:
Hi,

First, you can't get a plain micromotor to run as slow as 1 revolution per second. You will need some motor with a gear reduction or a small stepper motor.

How "Smooth" must the movement be? If it had 200 or 100 steps per revolution would that work?

I research some stepper motors and I found the NEMA 8. It has 200 steps per revolution and each phase draws 600 mA at 3.9 V. I could hook up a Easy Driver to drive this stepper motor and precisely control it's speed. Considering that this stepper motor runs at 3.9v, I could use a 9v battery to power everything, but I think that it would discharge pretty quickly, right? What do you guys think?

NEMA 8 Stepper Motor - Pololu - Stepper Motor: Bipolar, 200 Steps/Rev, 20×30mm, 3.9V, 0.6 A/Phase
Easy Driver - EasyDriver - Stepper Motor Driver - ROB-12779 - SparkFun Electronics

When you say "run everything on a 9 Volt battery", are you talking about smoke detector batteries, the ones with about 580 mAh capacity?

Due_unto:
When you say "run everything on a 9 Volt battery", are you talking about smoke detector batteries, the ones with about 580 mAh capacity?

Yes, those ones. But I think it would discharge very fast in just a few minutes. Maybe I will have to use a external power supply. I was trying to avoid using an external power supply, but considering that my enclosure is small, I won't be able to fit anything larger than 4 AA batteries.

Steppers use way more power than a DC gear motor. However a stepper can be much more accurate for
speed.

Neither will run from a 9V battery, not enough current.

A set of AA's is probably the way to go fro a DC motor. Battery powered stepper probably needs a big LiPo
pack or similar. What endurance do you want?

But you still have answered the question of accuracy - how accurate does the speed need to me?

Is this 50g disk balanced?

Maybe a Servo like this could do the job. As long as the final project is not a clock.

Hi,

I research some stepper motors and I found the NEMA 8. It has 200 steps per revolution and each phase draws 600 mA at 3.9 V.

Look for SMALL stepper motors, like those used on floppy disk drives and CD drives.