I cut down the old steel mirror cell so the mirror box could fit through a 30" door. The basic box of the mirror box is 5/8" Appleply with biscuit joinery on the corners. There is a shear web of 1/4 plywood in the middle of the box and the top has corner braces These combined with the mirror cell frame to make a very stiff but light box. The section above the shear web is there solely to hold the truss tube holders above the altitude bearings. Doing this meant I wouldn't have to notch the bearings or put the truss clamps inbound on the mirror box. I cut out large sections of the upper end of the box to lighten it and to make handles for lifting the scope.
The altitude bearings are made of l laminated Appleply and skinned with aluminum as recommended by the Dob-DriverII instructions. Blair, the owner of the scope, wanted a switch plate with lighted switches to control the fan, secondary heater, a light in the mirror box, and other functions on the scope. I put the light plate on the rear section of the mirror box. There are also plugs to bring juice from the battery to the mirror box and to power the secondary cage.
Rocker and Groundboard
After some calculations I figured that the rocker box would be lighter if I made it from steel instead of plywood. I ended up making it of both materials. The basic frame is steel and is made of 1 1/2" .095 mild steel tubing. Using this thickness allowed me to insert wheels and handles of 1 1/4" tubing into the hollow end of the 1 1/2" tubes. A full scale plot I made at a blueprint store served as a welding jig when glued to a plywood base. I used UHMW polyethylene to plug the ends of the tubes and to hold the bearings that came with the DobDriver for the latitude bearings. The altitude bearings all run on three small bearings instead of Teflon to reduce friction for the stepper motors. The remaining pad is a lifter mechanism for the the Dob-DriverII to lift the scope off the altitude stepper motor .This lifter is engaged with a knob to manually guide the scope. The knob that controls this is attached to an eccentric shaft with a flat on it that supports the pad. The altitude stepper motor is held in place with a plywood gusset that screws to the metal frame. The bottom of the rocker box is made of 5/8" Appleply and holds the azimuth driver motor. Using wood to mount the motors made them quieter and made it easier to mount. A12 amp hour gel cell, the DobDriver terminal strip, azimuth lifting clutch are mounted on the outboard edge of the rocker box. The groundboard is made off plywood with the outer edge 1 1/2" thick and the inner area 3/4". The axle runs in a bronze sleeve bearing.
Dob-DriverII
I chose the Dob-DriverII for tracking because it is easier and cheaper than an equatorial table. The original scope had had a failed DobDriver installation so I was somewhat concerned about the way I would attempt this. The main differences between a manual version of this scope and a DobDriver version are the clutching (lifting) mechanisms and the control of friction on all of the bearings. The altitude bearings and the ground board ride on roller bearings except when the telescope is operated manually. Then the lifting mechanisms ride on Teflon pads to add some friction when the scope is not on the drive wheels. The altitude bearing surfaces are aluminum to give the driver motor more bite. The azimuth drive has extra friction added by the battery weight. I ordered the medium torque steppers which I was told would be a good compromise between slewing speed and resolution if I decided to add the go-to computer upgrade. This whole system works very well and I was pleased with the tracking accuracy you can obtain after a couple of centerings. Another thing I liked about this system is the panning ability you have with the hand controller. I received excellent service from Paul at Tech2000 the Dob-DriverII company.
This telescope performs great thanks to the Steve Swayze mirror and I would change little if I had the chance. The tracking aspect is seductive and has me thinking of motorizing my own telescope
Contact: raynalds@spiritone.com
