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Thanks for the feedback Michael
I have no idea how long the battery will last! Having said that, I did experiment using 8 alkaline AA batteries in the mount holder. I found they lasted about 8 hours over cold winter nights here in Hobart - 4X 2 hour sessions with moderate slewing and they were starting to show signs of exhaustion. Also, you may have noticed on the Ioptron website that they in fact sell a purpose made battery counter weight suitable for all of their mounts. It is rated at 8 amp hours. It is also quite expensive compared with a DIY solution such as mine. So, I am confident that the 10 amp hour battery will last a long time, even allowing for only 50% discharging before recharging to ensure the long term health of the battery. I bought the correctly rated trickle charger with the battery which means it will always be ready for an observing session.
I aimed for the shaft to be reasonably close to the centre of gravity of the battery and cradle from top to bottom using a simple balancing exercise. However, as you mention, it is not critical as any discrepancy will be absorbed when balancing the system with the mount in the horizontal position.
Yes, I have tried balancing the counter weight against the scope by shortening one tripod leg. It's a bit scary! A while ago when I had all the components off the mount I weighed each item and measured their distance from the central balance point and did the calculations to work out the balance points for my different scope configurations.
One unexpected design shortcoming is that the locking knob that is tightened against the balance shaft to secure the dovetail clamp has a quite sharp point on it. So it has a very small bearing point on the shaft and has to be done up very tight to stop the whole cradle rotating on the shaft. At some stage I'll fashion a tool to hold the knob in the lathe and flatten the end to give a much greater bearing surface. Another solution would be a nylon tipped locking knob.
Cheers
Steve.
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