Re: New Dob Owner


On Sat, Oct 5, 2019 at 06:39 PM, <tj_slice@...> wrote:
I didn't want to drill the big hole in my base.  Without it, the smaller section of the pulley, that extends below the base, would have only been 10mm in diameter.  I didn't think it would be strong enough handle the load.  I figured the big hole would be hidden anyway.
I do it other way. A 10 mm diameter shaft fixed to lower disk which long enough to reach above upper disk can solve this. pulley can be fixed to shaft with a set screw. But when the mount need to be lifted, it can't overcome the lower disk weight and start sliding out of the shaft. Therefore the shaft should be threaded on both ends and fixed by nuts to withstand the weight of the lower disk.

I know this may be a more expensive solution, but it's important for me to avoid drilling in the mount. I want to make an "easy to install" design, so if anyone wants me to make one for him, he can install it without any other skill than tightening the screws.

I still don't know how your pulley fixed to lower disk. Is it only by that bolted joint?

The Az pulley is securely attached to the lower section of the mount and will not rotate.  The motor will be oriented vertically in a back corner of the mount.  If you lifted the entire thing off the ground, the lower part of the base would rotate around.  Since that will be fixed to the ground, and unable to rotate, the upper part of the mount, with the motor, will rotate instead.  I am sure the optical tube will end up being limited to around 80 degrees up when it impacts the motors, but that shouldn't be much of an issue.

Alt-Az tracking mounts have a limit at zenith which calls "zenith blind spot". I don't know how large is that circle for an arduino mega 2560 OnStep mount. Maybe Howard or more experienced users can answer. This can help us to decide if a 10 degrees overhead limit due to motor placement is worth it or not.
I want to install my motor near the edge of the disk, so it has more space vertically. but it needs a longer timing belt, which is not that important.
I want to use a sealed acid battery as a power supply because I think I won't find another source near my observing sites. These batteries are bulky and take more space, so handling a limited space between OTA, mount inner surfaces and upper disk edge is a real challenge for me.

Can anyone help how much Ah capacity for an OnStep controller (Mega 2560, two 1.3A motors and esp8266 for WiFi) is enough to tracking for at least 4 hours?

I am thinking about adding a couple of endstops to the Alt axiz.  The new pulley finished printig overnight, so I will get it installed and upload a new picture.

I'm waiting for your results. They are really helpful for me.

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