My astronomy project:
Design of a 3D-printed filter wheel

Content:

1. CAD design of a filter wheel
2. Chassi
3. Stepper motor
4. Gears
5. Shaft and Roller bearings
6. Home position sensor
7. Lid
8. Off-Axis guider
9. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

3: Stepper motor

The plan is to use a stepper motor to rotate the filter wheel with. A new or some used I already have.

Stepper motor 1:

I was recommended to use this stepper motor from a friend. It has a built in gearbox and is of unipolar design:

• https://www.digikey.se/ ... 28byj-48

The elongated screw holes for the stepper motor let it be adjusted against the gears. They also recommend this stepper motor in the documentation of myFilterWheel, but the 12 volt version.

Stepper motor 2:

An alternative stepper motor, this one I found in my desk. It came from an old printer, it has a diameter of 42 mm and is 14 mm high. The gear has 16 teeth and its module is about 0.55. The mounting holes is 49.5 mm apart. If I keep this gear I have to design a wheel gear with module 0.55 and 256 teeth. That give a gear ratio of 1:16, with 48 step / rev it gives a total of 768 steps / rev on the filter wheel. Two separated coils of 8 ohm each, 24 volt 500 mAmp, but I will use it with 12 volt.

More data of the stepper motor:

• https://nmbtc.com/ parts/ pm42s-048-hhc8/

A second design of the chassi where I moved the mountings holes to fit stepper motor 2. It's tight, I had to make space for it in the walls.

The pancake stepper motor installed on the chassi. Its flat design fits very well here. There will be an enclosure over the motor where I can install the Arduino and hardware driver for it.

The gear of the stepper motor protrude inside the chassi. I have to move the gear 4 mm outwards, but the shaft is too short for that.