Buying help: Motor for Smart-Blinds

Other Hardware Motors, Mechanics, Power and CNC
1

Hello. I am working on a project to automate my curtain windows.

I bought a standard sized dc servo motor that had an operational voltage of 4.8-6v (Model: DS04-NFC). It had high torque, but I greatly overestimated how many RPM's it would have. It said it had 0.22sec / 60 ° (at 4.8V). When I did the math, it should have been around 80RPM but when I received the motor, It was more like 30 RPM.

When shopping around for curtain rods or tubing material with a larger diameter to compensate for the low RPM, everything was either too expensive or too heavy to be considered for the project. Most curtain rods are sold with a mere 1" diameter, and I needed something like 3-4" diameters for my original estimated speed in order for it to open the blinds within a 7 sec-ish time frame.

Now I am shopping around for a faster motor, but I'll need something that can maintain an equal or greater torque. The last one was rated at 5.5 kg/cm of torque power. I estimate the curtains and the curtain rod to both be somewhere between 2-4 lbs combined, but having additional torque for these estimates would be even better.

I need the motor to go up and down (forward and reverse). From what I understand, continuous rotation servo motors are the best for this kind of thing (correct me if I'm wrong). I did not see many shopping results for "12v 100 rpm servo motor", so I'm a little confused if servo's are not the thing to use at these voltage ranges.

I could also get a forward-only motor and run them in a series, that way one is pulling down and the other is going up. However, if they are unidirectional, that means that the motors would not be running at the same time and would be fighting against the other's gears and I don't think this is a very good for the hardware.

I just need some shopping help, I am not very knowledgeable on all the available types of motors out there. I am only a mere Computer Science major :cry:

2

You can get bigger servos like below if a bigger servo would do the job.

3

I'm not exactly looking for a bigger servo.. I'm looking for a faster continuous servo that can still hold 2-4 lbs (preferably 3-5). Thanks for the input however.

4

Your arithmetic needs some work. 0.22sec / 60° = 1.32 sec / 360° = approx 45 rpm.

But apart from that have you looked at using geared DC motors. A search for 12V 100 rpm geared motors will find thousands of them most with plenty of torque. Then you'll need a motor driver (the advantage of servos is they contain their own motor driver) and probably limit switches. But your project or something very similar has been done many times and that's what is normally used.

Steve

5

The first step is to determine both the torque and speed required.

Calculate / determine / measure these, and convert to SI units (Nm for torque, radians/second for speed)

Multiply the values together and that's the power. Unless you get a motor adequate for the power required you'll only have grief, so you do need to figure this out.

You can trade torque for speed and vice versa using gearing - in fact for any smallish electric motor you will need reduction gearing in practice, torque is low, speed is fast for small motors.

Gearing isn't 100% efficient so you need to allow for more power using gears, 30 to 50% more is reasonable.

Electric motors do not self-brake. If you need the thing to resist movement when not operating you'll need a worm-gear drive which cannot be back-driven.