Initially when I conceived the SG-NG, I originally intended for it to be the first telescope that I have motorized, and I tentatively planned to use stepper motors for the drives. In thinking it over, I had one real concern. Namely, what kind of difficulties will I encounter in making a telescope that is capable of both motorized and manual operation. Besides, I feel that motor drive seems to violate the spirit of observing with a Dobsonian (Obviously my conscience is OK with elaborate controls, sensors and temperature-controlled mirrors). I don't want to wait for the telescope to slew to coordinates; I want to do that myself. All I really wanted was a way to indicate where I am pointing. In scrapping the go-to drive, I also eliminate those power hog motors. I still have to learn how to calculate between alt-az and celestial coordinates. While this is not the highest priority feature of the SG-NG, I will make sure that the addition of digital setting circles is not a afterthough.
The controller that I chose for a previous incarnation of this idea was probably not fast enough to track the encoder's quadrature outputs, so I came up with a design to track direction of rotation. That would mean all that was left was to count pulses and keep track of where home position was.
This page was last updated: November 7, 2013
September 8, 2011
A year ago, I thought that the idea of a motor drive was dead. There were too many issues I wasn't sure that I could- or wanted to- deal with. The number one issue was how to detach the drives and be able to manually move the scope. In fact, manual operation was (and is) intended to be the primary operating mode.
But a simple clutch plate assembly solves the problem for azimuth; an eccentric cam follower can be turned to shift the drive wheel from the side ring for altitude control. I plan to use stepper motors, and just realized that since they rotate in discrete steps, I could simply count steps and know the scope's position. A sensor on each axis could be used to orient the scope. I may still need encoders for manual operation, but this is an interesting thought.
November 16, 2011
I know this is 'Here we go again', but it looks like the go-to function is dead. I did get some good ideas at IDSSP 2011 on how to implement it. Although power consumption and mechanical complexity are compelling reasons to drop it, in the end, the death-blow likely will be the fact that I simply prefer to push the scope to position- this is a Dobsonian, after all. Still, this may not be the end of go-to for me, and my wanting encoders to tell me where I am pointing has not changed.
October 24, 2013
I am still working on ideas for motorizing the telescope. One requirement is that it can be mechanically disconnected, if desired. Owing to the evolving design, my philosophy of modular construction is evermore important. I now designate a box to control the drive motors and decode positioning as 'Siler'. A handheld control will be needed, and that box will be designated 'Harriman'. While Siler will be connected directly to the RS-485 network, Harriman will likely be direct connected to Siler. If I don't motorize, I will still need some form of position encoder. I was wondering if I could read tick marks made on the inside of the rocker with some kind of optical pickup.
November 7, 2013
I think that I have found a suitable worm gear for driving the rocker. If I can come up with a suitable clutch to disengage when desired, then I will add the gears now.
Initially when I conceived the SG-NG, I originally intended for it to be the first telescope that I have motorized, and I tentatively planned to use stepper motors for the drives. In thinking it over, I had one real concern. Namely, what kind of difficulties will I encounter in making a telescope that is capable of both motorized and manual operation. Besides, I feel that motor drive seems to violate the spirit of observing with a Dobsonian (Obviously my conscience is OK with elaborate controls, sensors and temperature-controlled mirrors). I don't want to wait for the telescope to slew to coordinates; I want to do that myself. All I really wanted was a way to indicate where I am pointing. In scrapping the go-to drive, I also eliminate those power hog motors. I still have to learn how to calculate between alt-az and celestial coordinates. While this is not the highest priority feature of the SG-NG, I will make sure that the addition of digital setting circles is not a afterthough.
