Wednesday, February 7, 2018

Getting There With The Big Bertha Rebuild

Last night it was not tracking.  I pulled the two AAA batteries and without load both showed 1.39V.  I was beginning to panic,  but I replaced them and measured the voltage across the motor terminals and found 5V.  A transformer somewhere?  I suggested to the maker an LED in the circuit to show dead battery.  He has already shipped his first unit with this addition.  Tonight I rolled Big Bertha out again and it is definitely tracking, but I do not have a good lock on North yet, and I do not have a lot of experience using star drift technique to fix this.  The good news is that even with that issue and a slight finder problem the digital setting circles are working well.  It put me almost exactly on M42.

The finder problem is that the finderscope that I have been using is a straight through finder not easy to use with a reflector (think of getting your neck down low enough to see through it when you are only about five feet from ground level.)   I need to replace it with a right angle one.   I have a Meade right angle scope on the small reflector that I can borrow to verify that it fits these rings before ordering a new one.

The good news is that the finderscope currently on Big Bertha will fit in the rings on the 6" refractor, where straight through works fine because you are at the rear of the telescope for the eyepiece.

The current finderscope on the refractor is something of a Frankenstein; the original 1" focal length reticle eyepiece was not repairable, and the only .965" barrel reticle eyepiece available was 18mm focal length, producing an 11x50mm finder, a bit narrow field.

M42 was pretty awesome.  Still needs some collimation after recent movements of hardware.

1 comment:

JLW III said...

What's you accuracy requirement? Less than one degree from true north?
This Device is expensive and probably overkill for your application, but it is totally cool and works by having multiple separated GPS antennae which measure the the time delay of reception of the signal from the individual satellites. Speed of light and all that.
I don't think I explained that too well. It has three antennae at the edges of the device. A signal from a satellite will hit one antenna first and the other two a short time later. From this and the fact that it can track multiple satellites simultaneously it can compute your heading.