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Assuming I am going to friction drive my focuser[s] by toothed belt and a timing pulley on the motor I need to establish some basic parameters. Distance between the axles is vitally important. [motor and focuser drive shaft] This distance can sometimes be fine adjusted by arranging the motor support to slide to provide a tighter or looser belt as actual performance dictates.
Number of teeth on the pulleys? The small one is known [or chosen] but the focuser knob is not a true toothed pulley. So the effective diameter of the focus knob must be measured. This would be measured as its maximum diameter plus one tooth depth. [or 2 x 1/2 a tooth depth if you prefer] to discover the knob's PCD. [Pitch circle diameter.] This number can then be multiplied by Pi to discover the diameter. Then divided by 2 for the number of teeth of a GT2 pulley.
The belt length is important for correct tension and based upon all the other factors above. I am assuming a GT2 belt with a 2mm tooth pitch x 6mm wide. This size is widely supported and the short pitch provides for a range of nicely small pulleys required for the motor shaft.
I searched for ages to find a really useful belt length calculator. This one is excellent:
Timing Belt Calculator - Belt Length Calculator | B&B Manufacturing
Just enter the details in the boxes on the left and the answers will pop up in the boxes on the right.
The calculator for the number of "large pulley" teeth can be repeatedly tried until the focuser knob Pitch Diameter [PCD] pops up on the right. Measure the actual focuser knob diameter [in mm] and work backwards to the effective number of teeth, of an imaginary pulley, using the calculator. Then add a tooth [or two] for a bit of slack in the belt. Remember that Pi is involved so Pi x 2mm for an added tooth height = 3 teeth or 6mm extra. A loose belt can always be tensioned with an idler. A tight belt will need the motor to be moved near to the focuser drive shaft to gain some slack.
15.00 Solar. Went over to the obs. Heavy cloud, northerly gales with only the briefest of solar views. My short TS helical focuser on my PST mod has, quite literally, just fallen in half! I've tied the binoviewer nosepiece up to a handle on the 7" for support.
Nothing obvious in WL. A nice, tall prom at my 8.00 [2.00 true] but nothing else. Gong H-a doesn't show the prom. A short clearing gave me superb views of a "beard" of proms on the bottom of the disk. [Straight through Binoviewer, so inverted. Let's call it north. Some disturbed plage near the top of my solar disk. [south]
I am definitely moving my laptop desk/shelf to the north side of the pier to stop myself being blinded at the keyboard after lunch. This will also put me nearer the eyepiece for these teasing days with lots of cloud but short, bright intervals. By the time I have moved the chair and adjusted the gas strut I've missed the moment.
A long period of cloud gave me the opportunity. The desk/shelf is now fixed onto the north side of the pier. With the IH2 alongside the laptop screen and the digital thermometer safely in the shade. Now I have to move the big digital clock because it is invisible where it is on the south obs. wall. Now south east.
Just enter the details in the boxes on the left and the answers will pop up in the boxes on the right.
The calculator for the number of "large pulley" teeth can be repeatedly tried until the focuser knob Pitch Diameter [PCD] pops up on the right. Measure the actual focuser knob diameter [in mm] and work backwards to the effective number of teeth, of an imaginary pulley, using the calculator. Then add a tooth [or two] for a bit of slack in the belt. Remember that Pi is involved so Pi x 2mm for an added tooth height = 3 teeth or 6mm extra. A loose belt can always be tensioned with an idler. A tight belt will need the motor to be moved near to the focuser drive shaft to gain some slack.
15.00 Solar. Went over to the obs. Heavy cloud, northerly gales with only the briefest of solar views. My short TS helical focuser on my PST mod has, quite literally, just fallen in half! I've tied the binoviewer nosepiece up to a handle on the 7" for support.
Nothing obvious in WL. A nice, tall prom at my 8.00 [2.00 true] but nothing else. Gong H-a doesn't show the prom. A short clearing gave me superb views of a "beard" of proms on the bottom of the disk. [Straight through Binoviewer, so inverted. Let's call it north. Some disturbed plage near the top of my solar disk. [south]
I am definitely moving my laptop desk/shelf to the north side of the pier to stop myself being blinded at the keyboard after lunch. This will also put me nearer the eyepiece for these teasing days with lots of cloud but short, bright intervals. By the time I have moved the chair and adjusted the gas strut I've missed the moment.
A long period of cloud gave me the opportunity. The desk/shelf is now fixed onto the north side of the pier. With the IH2 alongside the laptop screen and the digital thermometer safely in the shade. Now I have to move the big digital clock because it is invisible where it is on the south obs. wall. Now south east.
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