*
Sunday afternoon was much more cloudy. So I sat at the laptop in the observatory in my warm, but old and scruffy, down jacket. Just don't stand downwind of me if you want to avoid being "feathered." Bring your own tar if you're into that sort of thing.
Following a very instructive and illuminating discussion on an astro forum, I ordered a relatively cheap[?] Skywatcher, [auto?]focuser, motor system. A simple, geared DC motor is controlled by a lead back to a control box with 9V drive battery, forward and reverse buttons and a small, speed control knob.
Sky-Watcher Auto Focuser | First Light Optics
I don't plan to use the direct coupler between the motor and focuser shaft as the manufacturer intended. Instead, I will use a timing pulley and belt to provide a friction drive on the focuser's own adjustment knob. This allows the belt to slip safely before damage can be done to the focuser mechanism. I presume the motor lacks the power to do much damage anyway. There are loads of YT videos of SW motor "autofocuser" users. A whole variety of drives is employed.
Seemingly identical systems, to the Skywatcher, run to almost double the price when another label is applied at the same Chinese factory. So shop around if you are tempted to try one. The motor could easily be used for other duties. Including adjusting the focus on a camera lens ring via a timing belt or even a strong rubber band or motor pulley and O-ring. Even rubber drive wheels are employed where low drive torque is required.
With friction drives there is no need to match the tooth count or pitch of the device being driven. Available torque is a complete unknown until the goodies arrive in the post. I am led to believe the focuser's linear movement is quite slow but easily adjustable. Which sounds like a distinct advantage for the asking price.
For rather more sophistication, without costing the earth, an add on "box of tricks" can be used to control this simple DC motor drive. This box provides repeated returns to a chosen draw tube position via software. Even the speed of the motor can be dialed right down to an imperceptible crawl for very fine focusing for imaging. Well worth further investigating, I think.
HitecAstro DC Focus | First Light Optics
Meanwhile, "computer controlled" stepper motor, focusing systems start at around 6x the price of the bare, £50 equivalent, Skywatcher kit. Then climb on up to cost more than the retail price of a very large, very high end, US focuser.
These much more complex systems [and vital software] count the motor turns as a means to judging steps of linear drawtube movement. Then they can accurately return the focuser draw tube to a precise point in its range. Or even several points if desired. End stop monitoring is provided as standard to protect the focuser mechanism from the much more powerful motors.
This always requires a rigid connection between focuser and motor to avoid loss of relative position. Belts would have to be pitch matched to toothed pulleys to remove all chance of slippage. Though many motors just clumsily, stick out sideways from the end of the original, focuser shaft with a direct coupler to a previously removed focuser knob. Then often compound the acute injury to the senses. How? By adding a horizontal cable connection onto the very end of the already "sticky out" motor. WTF?
Are these horribly failed systems all designed by non-astronomers in a Chinese factory? How dare they charge these ridiculous prices for such physical abominations? Folding the motor neatly over the focuser drive shaft with gears, or a timing belt and toothed pulleys, provides a compact and stealthy adaptation of all too obvious sophistication. Are all such tragically poor, Chinese technology designs the result of Communist Party nepotism? Or are they just building what they are asked to by hideously inadequate Western
I've just watched a YT video of the proud designer of a very expensive motor focuser system struggle to fit his own mechanical monstrosity onto a real FT focuser. Did he so lack experience, or basic common sense, that he never though to provide a cable socket below his obscenely projecting motor? Or was he just a closet "willy waver?"
Some stepper motor systems can provide true autofocusing via supporting software. This allows the remote imager to achieve sharp images on a telescope and camera system sited outside in the garden or observatory. Or in another country right across the globe. Astronomical telescope hosting in dark sites rely heavily on such accurate focusing systems.
There are many commercial competitors in this motor focusing field. All with their own fan base and detractors. They all try to emulate the remote systems enjoyed by professional astronomers. Who may not want to acclimatise to high altitude telescopes in the biting cold of mountain tops on the other side of the world. All to obtain images and data for their projects and to support theoretical work. Many great observatories have remote control. Even if that just means the real astronomers are sited in more comfortable accommodation further down the mountain.
*
No comments:
Post a Comment