I tried the upgraded autoguiding tracker again on Wednesday and the results improved quite a bit. I used a 250mm lens to image the LMC. The following is a photo of the PDH graph showing the tracking error. The error is a small fraction of pixel. It has improved a lot since the previous test where the typical tracking error was ±3 pixels.
The resulting images of the LMC are not great due to the light polution but the tracking is starting to show promise.This is a single image (no darks or flats) taken at 60mm, f/2.8, 120 seconds and ISO 800 showing some round stars. Some cropping, levels and stretching was done with Lightroom 4.
This is the setup I used:
I used a Canon 18-55mm lens for the guide webcam. Tracking accuracy will improve a lot if I increase the focal length for the guiding, maybe use a 18-135mm. The zoom works well on the guide camera to find a suitable guide star.
The advantage of this mount is that it can take a bit of weight. I tried to mount an Orion EON 80mm on and it did not complain too much. Maybe I will need to modify a bracket to make sure the camera mount ball head cant slip with the 80mm scope. I will try that next.
Here is the latest version of the Arduino sketch: Stepper Motor sketch (pdf download)