Motor selection: Astro Photo of Pulsar

Projects General Guidance
1

I want a motor rotating precisely to 1800rpm. What would be my best choice?

I tried Stepper motor, but could not figure how to make it turn fast enough.
I tried Servo motor, unfortunately it was a 180deg.
I'm to the point I need to buy Servo continuous 360deg., but read that encoder is for control only, not a position reading for precision. (I still don't know if it will be necessary to have a loop back control.) **Does a servo with encoder exist?

For your comprehension: my project goal is to take astrophotography of a pulsar when it's light is minimum (freq: 29.9Hz). Imagine I want to picture someone close to to a stroboscopic light in a bar!! So, a rotating disk (dia: 6 inch) with hole (3/4 inch) will play the shutter function. Exposure time expected of 2 minutes.

The motor speed may probably be reduced with more holes in the rotating disk (maximum 4) so RPM could also be 900, 600 or 450.

¨-_-¨ It shoud be easy but it's HardWeKnow!!

2

How consistent does the RPM need to be? What is your budget?

3

A DC motor, driver, power supply, encoder, a calibration switch, a home switch. There are plenty of decoders having different resolutions. Everyting from small to 4096 exist.
What is the load, the stuff being turned around?

4

The best choice is a synchronous AC motor for your local mains frequency and gears to set the output speed to the 1800 RPM you need.

5

A pulsar is as precise as an atomic clock.
I only discovered one experiment of what we want to do, and there is no details of setup and parameters. My telescope operator expect at first an exposure time of 1 - 2 minutes.
For the budget, around <100$cad for the jig. A commercial chopper wheel is about 2000$, we cannot afford that price just to try.

6

Over long time periods sure. But that wasn't my question.

You have a rotating wheel. How precisely does that wheel need to hold it's rotational speed? Can it vary +- 10 RPM over a few seconds?

7

I have a feeling this may be occurring in a dark area away from city lights. It might be difficult to have an AC source, so DC from a car battery or what not might be a more appropriate solution.

8

The load is quite small, I'll perform the first experiments with antique vinyl audio disk. Afterward, I'll maybe use metal sheet.
The challenge is to have the weight well balance; as it's a fast rotation small off-balance will induce crazy vibrations and instability.

9

Perhaps so, but the question was about the best motor, etc. to maintain exactly 1800 rpm.

10

For the moment, I still don't know. But I'll tend to minimise the variation as much as technology and my budget may offer. The quality of the picture will be limited by the amount of light I catch from the pulsar; smaller the better.

There are 2 parameters I'm facing to:

  1. Get the right speed; 2) synchronize the off-pulsar timing.
    I expect a lot of try and errors to have just 1 decent result.
    I'm not finish to ask for help.
11

I'm thinking something like below or similar, then adjust the hole spacing and amount of holes to fit. Use the encoder to find the RPM and tweak it as necessary until you hopefully get stable enough for it to work.

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12

How small? Know that rotating a disc the radius is important. The larger the radius the higher is the inertia.

13

This Motor will work for your project.

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14

If you use that (or any other AC motor) be sure you understand the wiring and any additional hardware needed. Controller if needed, motor capacitor, etc.

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15

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