Spoke with a Gent at http://partsvault.com/ about the A3977 Ic's. He sells only in large volumes. Though he mentioned we could get one from www.newarkinone.com. He too is instrested in Astronomy and i asked him to come have a look. He also has stepper motors with very low step angle for about $20. These were made for a specific client with specific needs. But the price is for 100+ units.
i am fairly confident, that the surplus guys in aussie will keep the steppers up to us for a fair while.
for a hand controller for the steppers, then i think el can be roped in for advise. the parts are easily sourced and we can make our own controllers if needs be.
by the way, very happy with usb controller so far... have inerfaced with pc and now starting to work out different currents, different speeds, etc etc
Dave, have you given much consideration to how you are going to mount the Motors on the DOB? And the drive mechanisim? Gearing? etc. Can you share your thoughts on these so far?
I was thinking a belt drive for Alt like the one used in the Dob Driver II systems by Tech2000. Basically attaching a large steel flywheel to the Alt bolt and then rotating that with a belt attached to a motor bellow the alt. We also need to consider the forces exerted on this by the wesge. Not sure how much stress the springs that hold mine can handle.
As to the Az, i have neadle bearings and i have replaced my pivot bolt with a fixed bolt from Wildcard Innovations to mount my encoder. Someone mentioned earlier about using Selleys KneadIT. I have seen a photo of this done somewhere i will try and find it.
and then choose design b
7225(00) flanged housings can be supplied for end shaft arrangements (design A, fig) or for through shaft arrangements (design B, fig).
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i reckon if you can fit a 20mm tube or solid aluminium to the top base and then pass it thru one of these 7225(00) flanged housings that is connected to the base, then the weight of the telescope can be supported at an angle of up to 50 degrees.
i have spent alot of time discussing with engineering shops today and the best idea was a trailer wheel hub connects and rolls freely on the bearings. now you can buy the hubs already to go and would work straight away, but i reckon it is at least 15 kg!!!
i will check the price of the above housing, an 20mm axle say 150mm long, a bush with grub screw that can be put around the axle that protudes thru the top so it can take the drive unit either pulley and encoders etc
i will draw and submit tonight, and cc wombat.
if it works then we have only one central locating bearing system that works either sitting flat or on the angle!!
Wheel out Mick's DOb Buggy which now has a 150mm x 20mm aluminium piece of rod centred on it.
Review attached diagram
place roller bearing over aluminium rod
place bottom dob base over aluminium rod
screw in flanged housed bearing and screw into place
place another roller bearing over aluminium rod
place top dob base over aluminiun rod
place 2 piece clamp over aluminiium rod and screw tight.
place pulley for motor driving and then dsc or whatever on top of this
ok
if going to use in alt/az mode then leave as is and alst/az away
if going into wedge mode, then leave unit flat for the moment
line up with known star near the southern cross, enter co-ordinates
step to next near by known star star , enter co-ordinates.
now ask system to step to southern celestrial pole and then lock bottom base to dob base. This should be very good polar alignment!
raise platform to required angle and lock
base motor can now be a ra tracking
Please have a good think and see if i have missed anything.
one thing i have just thought of is that the support from the buggy that holds the wedge up will have to rotate with the bottom base so that it too is aligned with the pole. Mick???
By the way, i have bought a drawing pad and this is my first go with it, it was a lot of fun!
Yes Dave. Don't worry, I've been keeping a close eye on this thread lol.
I for one am having trouble picturing it...call me stupid..or it could be the fact of me never having clapped eyes on a dob mount, except in a few pics. I'm sure you know what your doing though. Need piccies mate...or detailed drawings....
Ok some good ideas there.. a couple of points to consider.
1. The wedge in mikes buggy is hollow. so what is to hold the ground base of the dob to the buggy??
2. whats holding the two bases apart... the weight of the dob would tend to tip the rocker base on to the ground base. At present there is a thing plate of nedle bearings or magic sliders or teflon pads etc etc.
3. why does the wedge support need to rotate?? Dont understand this one.
4. What about Dec (alt) motor or would this be optional, if optional need a clutch to stop dec movement.
Features to add.
It would be nice to have encoder hole bored into the aluminium axle with a grub screw.
Perhaps a grove in the rod for a belt. Or groves for a worm gear.
Also Dave, if this is to be a kit people would buy then perhaps it would be better to have a new rocker box that can work with any a variety of OTA's. This way not damge need be done to your original rocker box. And it leaves the design of the rocker box open for us to explore. I guess with this method people with a homemade dob could also use the rocker box buggy.
i have looked at some trailer couplings today and there are some roller bearings that are 20mm high, also, you could put 4 bearings at the outer diameter
with the polar alignment, if you set the dob buggy up roughly south and then whilst in alt/z mode, step to exact southern celestial pole, the support would have to swing as well , so that when you lift up the base to 50 degrees, then the support is at the exact northern edge
i am thinking that dec motorizing is included, so that like you say the scope does not put excess pressure on the springs etc
also there would need to be room on the axle for pulley, decs etc as you say
the wedge will have a cover fitted once l get hold of a dob for a trial fit, the base of the wedge does not have to rotate as the buggy itself will face the required direction.
I am looking to to drive by laptop, a few guys ave mentioned hand controller, which i am not sure how to build.
I have started on the interface to run on the laptop and then the internet version
It will allow for different step stepper motors, different reductions, different mounts etc
However i can program for the windows hand held platform ie pda's. would that be something you guys would want if i can link the pda to the usb controllers?
