Takahashi JP equatorial mount GOTO conversion

This is a GOTO conversion for Takahashi JP equatorial mount by using Losmandy Gemini-2 control system. 

Takahashi JP equatorial mount is vintage and yet classical. Here are simple ways to convert it into the modern GOTO system by using Losmandy Gemini-2 control system. 

Two methods can be applied, one is gear-driven via pinions & gears, another is belt-driven via pulley wheels. For gear drive modification, almost all of the original pinions & gears can be kept intact (except those old motors) to maintain its old school favor, however, the slewing movement is kind of noisy. And for belt drive modification, it is less noisier during slewing process relatively .

For JP mounts, RA wheel has 240T (teeth) & DEC wheel has 144T; RA worm gear is 0.8 MOD 48T and DEC worm gear is 0.7 MOD 70T. And the original RA motor pinion is 0.8 MOD 16T & the original DEC motor pinion is 0.7 MOD 14T, so RA gear reduction factor is 1:3 (48/16) & DEC gear reduction factor is 1:5 (70/14), and overall gear reduction for both RA & DEC are 720 (240x3 & 144x5) originally.  

To match the gearbox of Gemini-2 servo motors, one can simply choose pinion with 0.8 MOD 16T (or 24T with higher speed but lesser torque) for RA servo, and pinion with 0.7 MOD 14T (or 21T with higher speed but lesser torque) for DEC servo. Since the reduction factor of Gemini gearbox is 1:25, so the overall reduction rates for both RA & DEC are 18000 steps per round (720x25).

For pulley wheel modification, one can simply choose those GT2 pulleys to match 1:3 RA reduction factor & 1:5 DEC reduction factor. Intuitively choose GT2 48T & 16T pair for RA, and GT2 70T & 14T pair for DEC. The pulley belt can be either 6mm or 10mm in width.  

Since the RA c-c distance between 48T pulley wheel & 16T pulley wheel is around 59mm; and the DEC c-c distance between 70T pulley wheel & 14T pulley wheel is around 39mm. Therefore, RA GT2 pulley belt with length 186mm (c-c distance 60.14mm) and DEC GT2 pulley belt with length 172mm (c-c distance 40.3mm) are selected.

Note that both of RA & DEC worm axis diameter are 9mm, and the axis diameter of Gemini gearbox is 3/16" (about 4.7625mm), so corresponding gear & pulley center holes needed to be chosen or processed carefully for perfect engagement.

The following table shows some relevant information for “Gemini Settings of Gemini Telescope Setup”. In the page of “Advanced Gemini Settings [settings from Gemini]”, choose Mount Type as Custom under the “Controller Settings” area.  In the “Speed Settings” area, input both “Manual Slew Speed” & “Goto Slew Speed” as 800 (although, with 15kg load,  it can slew as fast as 1100x without being stalled). In the area of “Custom Mount Settings”, fill in the corresponding information from the following table. Note that “Steps per Worm Revolution” will be calculated automatically by the system. It seems that Steps per Worm Revolution = Spur Gear Ratio x Servo Encoder Resolution x Servo Encoder Multiplier.

Finally, two M10-1.5 x 25mm adjustable clamping lever handles  & M10-1.5 nylon insert hex lock nuts are required to engage the gearbox and corresponding  gears or pulley wheels.

p.s. M10-1.5 x 25mm adjustable clamping lever handles & M10-1.5 nylon insert hex lock nuts can be purchased from Amazon, for examples,

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https://www.amazon.ca/uxcell%C2%AE-1-25mm-Insert-Carbon-Plated/dp/B07M5WNVJC/ref=sr_1_29?crid=2OVNVESS94TA3&dib=eyJ2IjoiMSJ9.sgtMjQgPh0Hs-7YWIHZqcdpDfIPmNRWLnUMtsyN_rscJqQa2esnho83Rkk-yxoljCqLbMkyy8-vgWRv8WIxKBBhiFAr_lsHiygE2_e-EC7RHFMXtUf8u02isn5EuwqcNmAfGyoV9S0UqvHazFZbdvTQCIdAfDCQCetzBJEtOs02OvWKpSxYGuLsww1zPXAtJCI4sFydj8v6Q4N8vytKIJbaOz0SD96HQFJRFoImxQ6V7usInrjHiNyUtHrFwusREXimsihne2c6AQ3bqTJptj1_PEbJYxQuQ29GD2rTqBtc.s9tec5gmZgnpf462jYpx2Lx6pPuB6APhly8TwFsXZsg&dib_tag=se&keywords=M10%2Bhex%2Bnut&qid=1753769170&s=hi&sprefix=m10%2Bhex%2Bnut%2Ctools%2C280&sr=1-29&th=1

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