Wednesday, November 02, 2011

The Quest for a motor for my Mark-X


The motor arrived in perfect condition, however, the shaft coupler is missing and thus I will probably need to buy one myself.  On the other hand, I'm delighted to see its quality, the buttons were very nice to press and the pin on the connector to the hand controller is just thick and strong!  I'll need to built a power supply for it, and the seller reminds me that it's center negative and it's running at 9V, and thus a 8AA rechargeable will be about right!

After verifying that the motor is indeed working, I shall find a suitable shaft coupler for it and also how to mount it to the Mark-X, finally, I will need to find a replacement crystal oscillator for 126 teeth.


While waiting for the delivery, I've searched some potential oscillator suppliers:

Mouser, I ordered from them before, trouble free and good range of stuff

RS Online


The motor and controller is now on its way to me, tracking number: LC308020755US

The seller was kind enough to tell me that the controller is center negative!  I should keep that in mind.  The first thing which I'm going to do is to put it on the mount, I guess that the shaft coupler will connect without big problem.  I shall see if the torque is enough and if I will need to improve the mounting stability, and maybe I will need a local machinist friend to help here.

Secondly, I will need to open up the controller to see how can I modify it from 180 to 126 teeth, I wish and I expect that it will be controlled by a crystal and than I can scale the frequency and buy a new one for it.  Exact matching might not be possible but I hope that it will be close enough for me to track like 5-10 minutes at, maybe say, 200mm focal length.

Found a scanned specification sheet of the motor/controller.  It has a part number of RMD-2401 and also a model number of CXD-1.  In the specification part, it was described as quartz stepping motor and thus I would probably be able to swap the quartz crystal in order to adapt it to 126 teeth.  The rated voltage is 9V and the allowance is from 4.5V to 12V.  It consumed 160mA and it supports clockwise, counter-clockwise, 4 times speed, and also temporary stop.

From the limited photographs, I believe it would be very easy to mount it to my Mark-X.


I'll try to buy a Japanese Carton mount motor and attempt to modify it myself.  It's the same motor for the Tele Vue system mount which has 180 teeth, since it's a very old model, and I suppose that it will be controlled by crystal and thus, the modification should be relatively simpler for me since I don't need a EPROM writer.  Of course, matching crystal is another hard story and an exact match is probably impossible but for tracking like several minutes should be perfectly okay, at least I tend to believe so.  Let's see if I can get a good deal.


There're some very cheap RA motor selling in ebay but the seller never response my request for shipping quote.  Not until I click buy-it-now, and then after a few days, I managed to get the shipping but it's 2x of the motor itself!  Of course, I will have to cancel it.


If I were to use gear pairs to match the gear ratio, maybe I should use a off-the-shelf motor with controller rather than to build everything from ground up by myself?  At least it seems more reliable?


I've two existing DC geared motor, it's rated at 5 RPM at 12V.

Tonight, I've tried to apply 2.4V DC to it and it runs, I did a very rough estimate and it's running at 1 RPM at 2.4V... Suppose that I have to get 0.0875 RPM, I will need to slow it down further by using a PWM controller first, and then I will be able to get 0.1 RPM.

To get 0.0875 RPM, I will need a pair of gear, for examples, 28 and 32 tooth gears as recommended by DAVIDG in cloudynight atm forum.

I've to check my existing gear inventory, and see what I should buy. 

I've a 35 tooth gear suitable for the motor, so I will need a 40 tooth gear for the worm gear shaft?

I've another 37 tooth gear suitable for the motor, so I will need a 42 tooth gear for the worm gear shaft?

No comments: