Electronic filter wheel mod for astrophotography, Need some help with the design :)

[robjh123]

Hello,

New here hello everyone! I would like to add a motor to my filter wheel so that it can be controlled via my laptop. I'm trying to make my Telescope/Astro photography set up completely remote control so I can operate it from inside, in the warm! Pretty much all there aside from being able to the change filters. In Astronomy I feel it's best to try and fully understand things and make your own solutions rather that just always buy stuff, electronic filter wheels are £300+ this one was £25.

Here's my filter wheel on my scope.

After some research I'm under the impression a stepper motor will be be best as I'd like to be able to set 1 of 3 positions not just on or off.

This kind of thing... http://www.ebay.co.uk/itm/5V-Steppe...al_Components_Supplies_ET&hash=item2c93c5be79

I'm not sure what I'd need to look into usb to serial then onto one of these boards... not sure any help or advice on how to control via usb or which motor/pulley/cog design to use and ideas on how to attach would be much appreciated thanks!

 

[robjh123]

Just found this on ebay, looks possibly suitable http://www.ebay.co.uk/itm/5-Axis-CN...ial_Automation_Control_ET&hash=item5d4b909d09

For anyone that's interested here's a picture from the other day of the Orion Nebula 5x 1 min exposures stacked.

 

[davenn]

HI Robjh123
welcome to the forums

Seems you are on the right path with the best way to control it. You are just going to need software for the laptop or a microprocessor for being able to get the stepper to take a specific number of steps to move the filterwheel between filter centre positions. ..... that's well outside my field .... others may be able to help

nice pic well done ! I also enjoy astrophotography. Took my first images some 45 yrs ago when ~ 10 yrs old. Had serious years during the 1980's and into the early '90's
and only recently got back into it in a serious way with my Canon 5D3 and some big lenses

just in case you are unaware of it .... about the best astro forum is Cloudy Nights
http://www.cloudynights.com/index

feel free to keep in touch with me I would like to see how you progress with the system as well as your photography

cheers
Dave

 

[Laplace]

If you are going the software controller route, then it may be worthwhile to investigate ASCOM compatibility.
http://ascom-standards.org/Downloads/FilterWheelDrivers.htm

But using a stepper motor presupposes a solid link between between the motor shaft and the filter wheel shaft so that an exact number of steps will bring the next filter into alignment. Direct shaft coupling, toothed gears, or a cog belt will provide that exactness. But any kind of friction drive will be subject to slippage and loss of mechanical registration which would then require a position feedback mechanism. Would just looking at the image provided by the camera be sufficient? If not, then maybe optical sensing holes drilled into the rim of the filter wheel? Also, there appear to be three leaf springs to center the filter position, so it may be possible to sense a change in shaft torque at that point. The point being that if there is to be a friction drive that leads to a feedback design, then there would not be much reason to use a stepper motor when a simpler motor could also take advantage of the position feedback.

 

[robjh123]

HI Robjh123
welcome to the forums

Seems you are on the right path with the best way to control it. You are just going to need software for the laptop or a microprocessor for being able to get the stepper to take a specific number of steps to move the filterwheel between filter centre positions. ..... that's well outside my field .... others may be able to help

nice pic well done ! I also enjoy astrophotography. Took my first images some 45 yrs ago when ~ 10 yrs old. Had serious years during the 1980's and into the early '90's
and only recently got back into it in a serious way with my Canon 5D3 and some big lenses

just in case you are unaware of it .... about the best astro forum is Cloudy Nights
http://www.cloudynights.com/index

feel free to keep in touch with me I would like to see how you progress with the system as well as your photography

cheers
Dave

Thanks for your kind reply, I have gone for a small stepper motor with a board to control it, stepperbee. http://www.pc-control.co.uk/stepperbee_info.htm

And thanks glad you liked the picture, I can't image how difficult it was using film back in the 80's, great resolution I image though.

I've signed up to cloudy nights

 

[robjh123]

If you are going the software controller route, then it may be worthwhile to investigate ASCOM compatibility.
http://ascom-standards.org/Downloads/FilterWheelDrivers.htm

But using a stepper motor presupposes a solid link between between the motor shaft and the filter wheel shaft so that an exact number of steps will bring the next filter into alignment. Direct shaft coupling, toothed gears, or a cog belt will provide that exactness. But any kind of friction drive will be subject to slippage and loss of mechanical registration which would then require a position feedback mechanism. Would just looking at the image provided by the camera be sufficient? If not, then maybe optical sensing holes drilled into the rim of the filter wheel? Also, there appear to be three leaf springs to center the filter position, so it may be possible to sense a change in shaft torque at that point. The point being that if there is to be a friction drive that leads to a feedback design, then there would not be much reason to use a stepper motor when a simpler motor could also take advantage of the position feedback.

Sensing a slight change in the shaft torque with standard dc motor is an extremely clever suggestion ! Unfortunately I ordered a stepper motor before reading your reply. I've gone for direct shaft coupling for the reason you mention. I will post some pictures tomorrow of the progress so far.

I am going the software control route. The link to the filter wheel drivers looks very interesting I've heard of the Ascom standards thing and need to look into it further. I have bought this http://www.pc-control.co.uk/stepperbee_info.htm and planned to make a VERY simple visual basic program to control it.