DIY Motorized Focuser for FSQ 106ED Telescope

The goal of this project was for the automated focusing system to have great holding torque (80Ncm) for heavy image trains (4-5kg) and very fine steps to accommodate the super tight FSQ106 critical focus zone.

The formula to calculate the critical focus zone on a telescope is :
CFZ = Focal Ratio * Focal Ratio * 2.2
For the FSQ106ED we have : CFZ = 5 * 5 * 2.2 = 55microns
So to be able to have perfect focus achieved we need every step on the motor to be 55microns or less for even better resolution.

The motor used on this build is geared and has a reduction of 250:3 which gives us 4000 steps per revolution.

One full revolution on the focuser coarse knob (where we are coupling our motor) makes the focuser move 29.8mm.
Now we have all the data we can do the maths 😛
(29.8mm * 1000) / 4000 = 7.45 microns per step.

The actual resolution achieved with this build is 7.45 microns per motor step!

Astrophotography – Moon Mosaic Part II

Date : 26/04/2020
Telescope: Vixen VC200L
Camera: ZWO ASI120MM-S

6 part mosaic comprised of 800 frames for each panel.
Stacked on registax and then assembled in Pixinsight.

The Moon today is in a Waxing Crescent Phase. A Waxing Crescent is the first Phase after the New Moon and is a great time to see the features of the moon’s surface. During this phase, the Moon can be seen in the western sky after the sun dips below the horizon at sunset. The moon is close to the sun in the sky and mostly dark except for the right edge of the moon which becomes brighter as the days get closer to the next phase which is the First Quarter with a 50% illumination.

Fix for Flutter error : No toolchains found in the NDK toolchains folder for ABI with prefix: mips64el-linux-android

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Trying to run a slightly older Flutter project, the build sometimes fails with the error :

No toolchains found in the NDK toolchains folder for ABI with prefix: mips64el-linux-android

The problem is that -> mips64el-linux-android is missing in the NDK as it got deprecated some time ago.

What usually 🙂 works is changing 2 files in the Android folder of the project.

Open android/gradle/gradle-wrapper.properties and change this line:

distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip

to this line:

distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip

Open android/build.gradle and change this line:

classpath 'com.android.tools.build:gradle:3.0.1'

to this:

classpath 'com.android.tools.build:gradle:3.1.2'

Do a : flutter clean and rebuild. Happy coding!

Lathe – Threading gear calculator

Having bought a lathe for various DIY projects back in 2015, i quickly discovered the need to cut some unusual thread pitches (Astronomy adapters in particular have some of the weirdest out there).

The lathe manual (or the housing of the transmission system :D) , usually provides some information regarding the gearing for the most used ones, such as 0.05mm, 0.1mm, 0.2mm, 0.4mm, 0.5mm, 1mm and so forth.

But nothing for lets say an M42x0.75 adapter widely used in photography and astronomy!

While looking through the web in 2016 for a lathe gear calculator there was none to be found, that took into consideration the spindle to gear A ratio.
The spindle in this specific lathe (and many other brands from what i have read ) has a ratio of 4.5 turns. So in order for gear A to make a full turn the spindle makes 4.5 turns.

Without this number the usual quadrant calculations for gearing lathes, obviously fails and your thread pitches are not what you have expected at all 😛

Here is a very crude calculator for finding out possible, combinations of gears in a metric lathe (that is, a lathe with a metric leadscrew although it can cut some imperial threads by approximation), in order to produce the desired pitch when cutting threads!

Do note that some of the produced combinations, are not feasible at all for the time being, but I will upgrade it when time permits.

Lathe threading gear calculator

Have fun!