Motorized 5" Telescope
Alt- and Az-bearings
The alt-shaft's D175 mm bearing disks got a 15 mm wide aluminium covered surface. Covering was actually easier job than I first though. The aluminium straip is little shorter that the disk's round length. The gap between ends is about 5 mm. I drilled holes to near the ends of the straip. Then the first end was fixed by a screw and the straip was bended around the disk. It helps if the disk is connected to the work bench by screws. Aluminium straip got it's round shape pretty easy and after fixing the second end with screw the work was almost done.Re-assembling and epoxy glue between the straip and the plywood and screws back and that was it. From the photo can be seen that both disks have well enough the same diameter.The az-shaft has a cetral tube and a standard flanged bearing unit (d=20 mm). I put the hand-pad and the alt-stepper wires through the tube and bearing. The bearing is inside the support box, fixed to the lower surface of the support box's cover. That way the bearing is not taking any room inside the fork where I have the alt-gears and the stepper motor. Under the fork is fixed 1,5 mm thick stainless steel plate. The fork assemble is then running on three ball transfer units. In practise the system works well but in the future I will change the fork and the support box construction so that the transfer units can be located on the bigger radius.
Gears
Both alt- and az-shafts are done by using a small planet gear (5:1) and a worm screw/wheel pair (50:1). The final ratio (app. 8:1) has a polyurethane cogged belt (10 mm wide), aluminium cogged wheel and a nylon disc. Originally the disc was made of plywood as shown left in the photo but the roundness was not perfect. So the disc was made from nylon in lathe to provide the accurate shape. The alt-shaft's last ratio has now a friction wheel drive. Telescope's mirror box has a shaped side plywood plates. Around the round faces of the plates 15 mm width aluminium strips have been fixed by a glue and two wood screws. I placed the electric board and az-gear unit inside the support box. The gear unit is rather well away from the dust, etc. Also this way I got as less as possible separate and loose parts to carry outside during observing nights.
The alt-shaft's D175 mm bearing disks got a 15 mm wide aluminium covered surface. Covering was actually easier job than I first though. The aluminium straip is little shorter that the disk's round length. The gap between ends is about 5 mm. I drilled holes to near the ends of the straip. Then the first end was fixed by a screw and the straip was bended around the disk. It helps if the disk is connected to the work bench by screws. Aluminium straip got it's round shape pretty easy and after fixing the second end with screw the work was almost done.Re-assembling and epoxy glue between the straip and the plywood and screws back and that was it. From the photo can be seen that both disks have well enough the same diameter.The az-shaft has a cetral tube and a standard flanged bearing unit (d=20 mm). I put the hand-pad and the alt-stepper wires through the tube and bearing. The bearing is inside the support box, fixed to the lower surface of the support box's cover. That way the bearing is not taking any room inside the fork where I have the alt-gears and the stepper motor. Under the fork is fixed 1,5 mm thick stainless steel plate. The fork assemble is then running on three ball transfer units. In practise the system works well but in the future I will change the fork and the support box construction so that the transfer units can be located on the bigger radius.
Gears
Both alt- and az-shafts are done by using a small planet gear (5:1) and a worm screw/wheel pair (50:1). The final ratio (app. 8:1) has a polyurethane cogged belt (10 mm wide), aluminium cogged wheel and a nylon disc. Originally the disc was made of plywood as shown left in the photo but the roundness was not perfect. So the disc was made from nylon in lathe to provide the accurate shape. The alt-shaft's last ratio has now a friction wheel drive. Telescope's mirror box has a shaped side plywood plates. Around the round faces of the plates 15 mm width aluminium strips have been fixed by a glue and two wood screws. I placed the electric board and az-gear unit inside the support box. The gear unit is rather well away from the dust, etc. Also this way I got as less as possible separate and loose parts to carry outside during observing nights.
The worm screw shaft's bearing supports are made of plywood. It was rather difficult to adjust to match the screw shaft to wheel and there might be a little vibration which may cause cap changings in the future. It would be better to make steel support for the screw shaft atleast. Between the stepper (Vexta 4,0V/1,1A) and the planet gear I placed a piece of plastic hose. Between the flange of the stepper and the plywood support is a 2 mm rubber plate to isolate vibrations. There is also the same rubber material under the worm screw support. I didn't have any plastic connection screws for the stepper but haven't yet noticed any need of them. Lately during re-construction of the whole telescope I also added flywheels on the stepper's shafts to get faster slewing speeds. That seems to work pretty well. Earlier the fastest slewing speeds were round 1...1,5 degrees/sec while now with flywheels they are app. 2 degrees/sec.In Alt-shaft may occur slipage and so happend during testing. There are tracks on the aluminium remembering that. So, if I should some day make more changings the first one would be making a threaded rod drive for the alt-shaft. Either by using nylon/steel rods as shown in many web-pages. I have thought that it might be possible to bend a steel M6 threaded rod around a plywood sector. At first the plywood would be covered by aluminium strip, then steel rod would be fixed at the first end, then bending and finally another end of the rod would be fixed. So, then there would be steel/steel rod drive. Would there be too much wearing of those rods? I do not think so. Well, have to try it some day...The worm wheel shaft was made at a workshop. I happend to find a couple of old "Stauff" pipe connectors in which standard ball bearings fitted just perpectly. Inside the connector is two bearings. I was little bit afraid of plastic connectors stability but haven't got any problems in visual use. In az-shaft case there is 10-teeth wheel connected on the shaft by two securing screws. That was at first a real problem! After a few minutes stepper driving the wheel was loose. I ended up to use "quick glue" and so far it has worked. Luckyly. So, it would be better to use atleast 15-teeth wheel because it is suitably bigger and allow to use M4 securing screws.
Plywood Works
The telescope tube part was little bit hard to make. First I made a frame by cutting two 15 mm plywood circles which I attached together via 3 pcs. plywood square bars. The round part is 4 mm thick plywood fixed with glue and screws over the frame. The rounding process took place by weting the outside surface of the plywood, rounding it around the steel tube and securing by a few piece of rope. After a night the plywood was dried and formed roundy form. The rest was quite easy to do execpt the desicion of the rounding start point. Well, afterwards thought the tube is not the best one. The frame bended a little bit clockwise and the cover plywood too. The result is that if you look the tube from one side it looks perfect but from another it is for sure enclined a little bit. Eyes won't lie!
Plywood Works
The telescope tube part was little bit hard to make. First I made a frame by cutting two 15 mm plywood circles which I attached together via 3 pcs. plywood square bars. The round part is 4 mm thick plywood fixed with glue and screws over the frame. The rounding process took place by weting the outside surface of the plywood, rounding it around the steel tube and securing by a few piece of rope. After a night the plywood was dried and formed roundy form. The rest was quite easy to do execpt the desicion of the rounding start point. Well, afterwards thought the tube is not the best one. The frame bended a little bit clockwise and the cover plywood too. The result is that if you look the tube from one side it looks perfect but from another it is for sure enclined a little bit. Eyes won't lie!
Copyright©2008 Aki Lötjönen
