Finally I have had some time to get my thoughts together on the matter of constructing an equatorial platform.
I was going to set up a web site and link to it but decided it was probably better to go the way I have and formed it into a pdf file. Hopefully it is not too bit at 300KB.
It's a great start, thanks for the info. I'm still not sure if I have the mechanical and woody skills to create one of these myself.. Not to mention, I don't have all the woodworking tools that would be required.
I think the wood working is the easy bit. You also need to fabricate metal bits for the drive and gearing, not to mention the electronics for controlling the stepper motor.
Originally posted by Starkler I think the wood working is the easy bit. You also need to fabricate metal bits for the drive and gearing, not to mention the electronics for controlling the stepper motor.
Yep,
The gearing for the motor is a bit of a worry but there are plenty of small motors with gears available from places like Dick Smith with the final speed known. That was the hard part using the motor I did, it was all experimental as the speed was unknown. As for the controls, if you have it in the right ball park with a standard DC motor just varying the current will vary the speed enough for you to get the tracking right. Unfortunately, as the batteries run down so does the speed so you have to do a bit of fiddling there.
That is where a stepper motor comes in. There is a lot of info on their control in the sites I have attached so if you are electronically inclined or want accurate tracking they are the way to go. That is why I am looking at the RA controllers to see if any are useful for what I am trying to do.
Rob, even if you build or buy an electronically REGULATED speed control, the actual rpm of the motor is never constant. I know from experience with my camera tracker & it has hardly any load on it & the output pulley rotates once per minute. You have to keep adjusting. Really the only way is to clock/step your platform for accuracy. I built a reg. speed control for a member who made a complete refractor, gearbox, mount and tripod,(A1 fitter & turner), but he still has to make very slight adjs. to the pot to keep the t'scope centred.
I've dabbled in electronics for about 40 yrs. and am still larnin'.
See pic of camera tracker drive.
Just the facts m'am.
Originally posted by Starkler Steppers are constant assuming they dont get stalled.
Sounds like a stepper is what I need though its surprising how good a normal DC motor is for visual use so long as the batteries are in good condition.
Rob, What I said is, that a simple electronically regulated speed control is not accurate. Stepper motors are accurate. They require a different circuit specifically designed to drive them. They are 2 different types of drives.
eg. 12/35 volts input > a 7805 regulator circuit (0 to 5 volts, adjustable, at 1 amp. out),> to motor/gearbox = NOT ACCURATE ENOUGH!
As stated, the 7805 is only an example. These CAN BE USED FIXED OR ADJUSTED for different output voltages or another reg. used to suit the motor input voltage.
It's hard to explain in great detail here.
Have attached sample.
Let me know if you req. more details.
Hi Rob , have you had a look at Mel Bartels web pages .
If you don't know who he is , he is sort of the Grand Master of telscope making and computer controll scopes namely DOBs in the amature world.
His site and links are full of info for the dob converter to get ideas.
if it's not there it's not worth it.
There is also a forum for the builder as well.
You will notice that he has controllers in various stages of construction for purchase as well that are for stepper and the new servo systems. The later I have just recieved and included a quick pic of.
I am in the middle of building a large EQ friction roller fork mount.
The systems will work on vertually any mount especially DOBs and conversion is not that dificult.
There is an explanation on the difference between stepper and dc servo systems and what each requires to function and track properly .
Originally posted by rmcpb Are you saying that stepper motors are not constant? If they aren't do you know what is, I thought they were the top dogs in this area.
AC servomotors.
Mind you, the ones I've been around recently (big Siemens ones) are a little bit pricey and are controlled and powered by a cabinet worth of stuff.
But they have crazy precision and dynamic performance.
Mojo has a friend (cousin's husband or something) who is an engineer and who will likely be able to make one of these for me, given some detailed, accurate and complete plans.
I say "detailed, accurate and complete" because he is an engineer, not an amateur astronomer. So he will make it as per the plans. If the plans are wrong, or incomplete, or make assumptions, he's not likely to know and so it may turn out wrong.
Can anyone recommend a site with a set of plans that are detailed, accurate and complete? It doesn't have to be the most complex one, because obviously i'm trying to keep the costs fairly minimal (it'll have to be posted from melbourne, too) and so don't need one with all the bells and whistles. And also one that's not so complex will have less room for error when he's making it.
I'm at 33 degrees South, I guess some adjustment needs to be in the plans for this?
It depends on the type of platform, the centre of gravity of your scope, type of driving method, latitude, the use of the platform (for one particular scope or a range of scopes or cameras).
In short, there would be no definitive plan, you will have to draw up a set for your needs and hope you get it right (that is why these are normally made by tinkerers as the plans are usually quite fluid). Just use the spreadsheet in the web site I quoted in the article for the actual platform. As for the driving system that is a whole different ballgame and depends on how finely balanced your setup is, the size of the motor used (influences the noise level and how adaptable the system is), standard DC versus stepper motor, tangent drive versus direct drive (my recommendation), how you plan to reset the platform, etc.
PM me if you want to carry this further as I have lots of ideas but that is what they are, just ideas which I am trying at present while my platform is in a million bits.
