Dome Actuation

[MikeMike Sharps]

Hi, I am lucky enough to have a fabulous ‘Home Observatory UK’ hexagonal observatory I am looking to simply automate the dome for extended Astro-photography sessions. I currently move the dome by hand every 20-25 mins. I have acquired a 330mm linear actuator- which is powerful enough. I can work the mechanical aspects but looking for help on the electrical side of timing & switching.  I need to operate a 30v DC motor (750w) every 10mins for a few seconds. Don’t seem to be able to find a suitable timer switch off the shelf, looked at Ardunio / Raspberry PI, but quickly got out of my depth. 
looking for simple ideas, anyone done similar thing or can provide some help. I’m a retired mech engineer so only have basic electronic skills. 
All help appreciated.  
Mike 
 

[skybadger]

Hi Mike. As an engineer I will now say those important  words , what are your requirements ? If you can rotate in a circle , a number of motors (between 1 and many) are probably easier to implement. They could be friction, belt and pinion or some other method of engagement but there are numerous open source and off the shelf solutions for that which would means your skills requirement can be kept to the appropriate level. 

Any details on the dome and physical layout ?

[BCN_Sean]

For the motor controller, I would be thinking of an Arduino (with LCD screen and a couple of buttons to adjust the sequence) and switching on and off a relay to drive the motor.  I know you've already said that you are out of your depth with that route, but it may be worth enquiring in a local community group, or the local college student union to see if there's anyone who'd be able to build you one locally.

[M40]

Hello Mike, get something like this..... https://uk.rs-online.com/web/p/timer-relays/8285158/

It's basically a timer that has a number of options in how it works i.e. pulse on/off for a time etc. Anyway, hope it helps.

[skybadger]

Or maybe someone here can provide you an ascom compliant dome driver ?

There are numerous large motor drivers out there, some for less than a tenner, that will work directly from a bidirectional switch. My dome shutter manual override works like that. 

 

[MikeMike Sharps]

My thanks to all that have replied  - some good suggestions that I will follow up. In response to sky badger, the picture below depicts the mechanism. Lower rail Is where the dome is mounted onto & allows 360 rotation. Above is another frame mounted on casters which allows the centre split roof to open. The rotating rail is set a fair bit outside of the internal observatory walls, making it difficult to mount a direct drive. A motor driven wheel could be mounted in a similar way to the castors but would rotate with the roof - care needed for control & power wires. I have looked at some of the popular GRP domes & drive mechanisms connected & controlled through ASCOM, but cannot see a way to emulate with this observatory design., hence a linear actuator. 
my requirements spec is fairly basic; need to rotate the roof in short ( few second) intervals & have a time delay of several minutes. If these times need to be easily varied (to allow for different scope elevations. I am looking for about 2 -3 hrs / 30 -45 degrees of rotation for a typical photography session. 
Many thanks again for all contributions. 
 

[skybadger]

Thanks Mike. It's not unsimilar to many other domes. A friction wheel driving on the  underneath of the dome rotation may do your job. Alternatively if your rotating internal or external profiles are round-ish, a motor could drive on that surface. 

My dome drives on the internal edge but still uses power and control electronics for the shutter motors which are powed from solar & battery and uses Wi-Fi to communicate with a central controller PC . Hence allowing continuous rotation and independent power. 

Either way, take a look at cytron power controllers from the likes of the robot parts websites, they are cheap and provide large currents for simple motor controls. 

[Nigella Bryant]

Interesting post, thanks. I too am looking to motorise my rotation of my older type pulsar dome this spring. I've got an old motor from a mobility scooter, a reverse forward and back turn on off box/switch and AC to DC power all working together at the moment. I'm building a rail and going to use a t-belt pulley and teeth belt T10 to drive the dome. I like the sound of adding a timer relay to the design to  continually give small movements when at the telescope.

[skybadger]

The problem with timers is the interval continually needs to change due to the changing alt, AZ movement rates. If you build yourself enough of a motor driver to drive the dome with switches, then you have enough to add the lesve dome control to for full dome auto control, or the velleman USB interface for the same. Both of these are open source on github or similar. Mines there too if you can do Arduino and some fairly simple soldering. 

 

[Robindonne]

I once build a hobby project that could be used in this setup.   It didnt have the drive system though.  But that would be possible by adding one motorized wheel in your wheel rail/system.   
 

The hobby project had 2 (ultrasonic)distance sensors.  One or two sensors attached to the dome and aimed at a solid point that moves around(your mount), could let the dome follow the movement of the mount.  
 

a slipping wheel in your rail wouldn’t cause any problems because it will ride the roof until the sensors measure the given needed distance
 

although you need some programming for this setup😬

Edited February 4, 2021 by Robindonne

[M40]

I have to be honest and say that this topic has been bugging me. I have no idea about guiding, tracking or tracking software. It's hopefully in the future for me sometime, just not now. But what I have been thinking about is dual tracking. A quick look and something like PHD can control a main and aux mount so could you for example, get a goto upgrade kit containing all the bits and bobs you need but rather than drive stepper motors drive relays to energise a motor control circuit?