Saturday, 30 April 2016

Telescope with Raspberry Pi - stepper motoring

On the few occasions that the weather has co-operated I have been testing tracking with the setup described earlier. It has not worked well. Tracking was very occasionally good, mostly mediocre and sometimes dire.

I have though much improved the wifi access by setting up an external access point. The signal is now excellent and remote desktop from inside to the pi on the 'scope works well. I used an outdoor ap with cheapo power over ethernet all stuck onto the house with a cheap aerial mounting kit from B&Q.
  1. 7dBi GSM 4G Penta-Band Panel Antenna N-Type
  2. ALFA TUBE2H 150Mbp/s 2.4Ghz Long Range Outdoor Ethernet WiFi AP/CPE with N-Type Connector
I wrote a trivial python script to pulse the ST4 interface to see what was happening at the coal face and it was not pretty.

At the 1.5x speed setting on the DD-1 controller pulses long enough to cause 3 steps were actually doing from 0 to 3 steps, very few were 3, and quite a lot were 0, this was with the mount indoors and no load. A bit of back pressure against the direction of movement made the situation significantly worse.

Increasing the speed setting to 2x helped quite a bit, but any significant load still saw the difference between intended steps and actual steps increase dramatically. I could hear the pulses on the motor, but they were not causing the motor to actually step.

I saw 2 ways forward:
  1. buy an EQ5 goto upgrade kit - these fit the old Vixen mounts with very little adaptation, but they cost around £300.
  2. go diy with a raspberry pi stepper motor HAT using the existing motors, cost circa £20.
And being keen to get to grips with stepper  motor magic for other reasons as well, I went with option 2.

Order has just arrived so I will be busy for a few days.........

Well some success, but not quite what I expected!

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