USB Focuser

[Rocket Pooch]

Hi Folks,

I have finished the first part of my focus software, I can now drive two stepper motors from my PC (main scope and guide scope) and see on the screen the progress of focus in say AstrArt and also see the steps taken to get there.  This has been quite simple using the stepper bee board.

I'm going to ask John P to help me with a slight stepper motor issue, they are getting warm, not hot, I don't know if this is normal or if I need to do something with them.

I'm going to look at adding an emergency switch to the focuser so I cannot focus too far in, this will be using one of the boards digital input, but this is the next step after getting it in a box and on the scope.

If anyone also wants to do this let me know and you can have a copy of the code and the parts needed to complete the project.

Chris



AstronomyFocus by chrissuddell, on Flickr

[Ian]

how warm is warm? I'm guessing you're driving them with a higher voltage than they're rated for. Or are you powering them when they're not moving? Cut the power when they're stationary...

[Rocket Pooch]

13.8v not 12v, and not help I', burning, just warm 80f?

[Ian]

hmm, tricky one. 80F isn't something that likely to really trouble the motors, but I'm surprised they're heating at all. Are they struggling to provide the torque and pulling max current? Do they cool down when they're not moving?

[Rocket Pooch]

Hi,

No issue with torque, and yep its cool now, odd eh!

Chris

[JohnP]

Chris - Depends on type of motor & controller you have . Some controllers provide fraction of a step control so even though your motor has say a step size of 1.8deg you can make steps of 1/2 or 1/4 or even 1/8 step but in order to do this & to keep the motor at a particular position current needs to flow all the time (as more than one coil will be energized) - In this instance things will warm up. Stepper motors (even small ones) draw quite a bit of current when energized. If you are only making single steps at a time (& say relying on gearing to give you the resolution) then motor/ electronics will only draw current & get warm when moving. You obviously don't want to be drawing current when focus position is reached else you will draining batteries etc.

John.

[Rocket Pooch]

Hi,

Ineed to work out if the board is doing half steps but there is no way to control that in the interface, maybe its just on all the time, which is not a problem if I turn off the power when focused.  Also I do have smaller motors I could use, the one thats on it is not small.

If its ok I'll bring it over to you so you can have a look see.

Chris

[The Thing]

Hi Chris,

To stop the motion before it goes too far all you need is to be able set a max and min  steps value for each motor. The Lakeside unit has a function to do this by stepping to each point at which you want to stop and recording the steps value. That way the unit just stops when it reaches the set points.

Duncan

[Rocket Pooch]

Hi,

Yep, thats easy and I can write it to an XML File, would just need to train the focuser for min max, thats why I'm keeping track of the steps, see the llittle box with the numbers in it.

Also, I could record the steps with combo's like different filters and cameras, I'd assume the focuser would be all the way in and then step out to the focus point, the only trick is turning the focus lock.

Chris

[mickw]

the only trick is turning the focus lock

If its a rack and pinion focuser, it wont need a lock, the motor would do it.

[Rocket Pooch]

Thats was a joke mick 

[Ian]

Sort of related, have you coded it to arrive at the preset focus position from the same direction each time to eliminate and backlash?

[Rocket Pooch]

Nope, just counts steps forward and backwards, neither it is temprature controlled.

[mickw]

Thats was a joke mick 

I knew that 

[The Thing]

Sort of related, have you coded it to arrive at the preset focus position from the same direction each time to eliminate and backlash?

The Lakeside controller lets you put in figure for backlash compensation. And it also will record Park, Un-park (useful for winding in the rack before packing up) and three other positions. It would be cool to have named presets for combinations of gear, smart idea.