18 Replies Latest reply on Apr 4, 2019 2:15 PM by colporteur

    how to maka a telescope turn with high precision?

    simon.ganne

      Hey everyone, I'm preparing myself because I need to build a project next year and write a thesis about it. My project is an automated telescope. Now I was wondering how I could turn the telescope around with some kind of motors at a precision of at least 1 degree. Has anyone experience with this kind of stuff or someone who has an idea?

        • Re: how to maka a telescope turn with high precision?
          ravi butani

          Stepper motor will be best... Nema17 is standard low cost stepper motor mostly you find in 3d printers...

          Further for automatic telescope you need 3 stepper motors for azimuth angle, elevation angle and one for change focus..

          For control stepper motors you can use arduino uno or Arduino mega with stepper motor driver shield based on A4988 or other drivers from allegro.

          Also you will need magnetometer hmc5883l for get reference of azimuth respect to North...

          You can use some online tool to get azimuth elevation angle of known starts with reference to geographic location of telescope...

          2 of 2 people found this helpful
          • Re: how to maka a telescope turn with high precision?
            ravi butani

            In continuation with previous reply... You can write java, python or c software to calculate and pass azimuth elevation angle from host computer to arduino via usb...

            Or make Android app that do similar thing via Bluetooth and arduino with hc05 bluetooth module

            1 of 1 people found this helpful
            • Re: how to maka a telescope turn with high precision?
              ravi butani

              Ohh as you have posted your question in raspberry pi group... Another solution is use raspberry pi itself as standalone host computer and stepper motor controller.. with onboard WiFi and Bluetooth on raspberry pi ... It will be true automatic internet connected IoT based telescope which you can control from anywhere in the world and get feed of video of image in realtime

              1 of 1 people found this helpful
              • Re: how to maka a telescope turn with high precision?
                jw0752

                Hi Simon,

                You can greatly multiply the precision if you put a worm gear on the stepper and use it to drive a large gear.

                John

                3 of 3 people found this helpful
                • Re: how to maka a telescope turn with high precision?
                  jw0752

                  Hi Simon,

                  For the Azmuth a clock motor would be better than a stepper as you will see a quantized step with the stepper and the clock motor would be able to track smoothly.

                  John

                  4 of 4 people found this helpful
                  • Re: how to maka a telescope turn with high precision?
                    Roger Wolff

                    I would think that having a stepper control the focus would be unnecessary. It depends a bit on what you're looking at, but when stars are far away, planets (other than earth) are not close enough to require a change-of-focus.

                     

                    Even when you gear things down, the steps from a stepper will be noticeable if you're going to try track the stars. I would recommend the strategy: Point the telescope at the area you're interested in and take a series of pictures. Combine the series of pictures using software. This should give you better results than trying to keep sub-pixel accuracy in pointing the scope. The software to do that was described on Hackaday. Not sure if it is already on github.

                    4 of 4 people found this helpful
                    • Re: how to maka a telescope turn with high precision?
                      DAB

                      There are many examples of automated telescopes with open source designs and software available with a websearch.

                       

                      Depending upon what you are doing, you will need much better than 1 degree accuracy.

                       

                      The stepper motor approach is probably the cleanest, though you might want to add a star tracker camera to get smooth tracking on star targets.

                      You will also need to account for sun, moon, planet and comet tracking.

                      For Asteroids you usually need time exposures, so you use the star trackers.

                       

                      The timing issues are fairly straight forward depending upon your telescope mount.

                      Are you using an Azimuth/elevation or equatorial mount?

                       

                      DAB

                      4 of 4 people found this helpful
                      • Re: how to maka a telescope turn with high precision?
                        Jan Cumps

                        Maybe ask my pal thecurrensource?

                         

                        2 of 2 people found this helpful
                        • Re: how to maka a telescope turn with high precision?
                          simon.ganne

                          thanks for the replies but I need a way to motorize it. anyone an idea?

                            • Re: how to maka a telescope turn with high precision?
                              fmilburn

                              If you google “diy motorized telescope mount” or something similar you will find lots of examples.  Also check astronomy forums.  In my opinion, the motor is the easy part.  The mount and mechanical parts, especially for a large telescope can be challenging.

                               

                              I have stepper motors with worm gears on my telescope with a german equitorial mount.  I also made a “barn door” mount once for my camera that was driven by a stepper.  This is a very easy mount to make and It is relatively easy to maintain one degree precision over an extended period with such a setup.  Google...

                               

                              BTW, It isn’t clear to me whether you are trying to find a spot in the sky (slew) with one degree precision or track.  Tracking only requires one motor for one degree precision over moderate timeframes with an equitorial mount and finding requires two.

                              2 of 2 people found this helpful
                            • Re: how to maka a telescope turn with high precision?
                              schismata53

                              I'm experimenting with telescope tracking at the moment. I've used a NEMA17 stepper motor with a 5:1 gearbox and used a DRV8825 driver controlled by Arduino. In theory you can make stepper motors more smooth using microstepping but in practice I've found it difficult to get the speed consistent. It surges for some reason. Perhaps I can improve it with a better driver or a higher gear ratio. You can get stepper motors with 100:1 gearboxes online.

                               

                              Regarding precision the moon is about 1/2 degree or 30 arcminutes. Venus at it's largest is about 1 arcminute. I would suggest for accurate tracking for astrophotography you need to aim for around 1 arcsecond. I.e. one step of the stepper motor is usually 1.8 degree which is 1.8 x 3600 = 6480 arcseconds. If you gear it down by a 1:100 gearbox you get 64.8 arcseconds. That should reduce further by the ratio of the output of your gearbox to the gear it is driving which depends on your design but let's say it 10:1 which gives you 6.48 arcseconds. That's not bad but would probably still be noticeable. It's roughly the separation of the double stars in Alpha Centauri. With 4x or 8x microstepping you would just make it if you could get your microstepping to be smooth.

                               

                              The precision of the equatorial axis is most important as it is the one that does the tracking. The declination is less so once you're on the object this axis doesn't move. If you don't have an equatorial mount you can track by moving both motors at the right speed (which is a little complicated) but even with perfect tracking the image slowly rotates which is a problem for astrophotography.

                               

                              I personally think that a motor to drive focus is more important than the declination axis. Whenever you try to change the focus manually you bump the telescope and have to wait for it to settle before you can see the results of your focusing unless it's a very stable telescope. If people with different eyesight are looking through it, each person needs to focus it for their own eye. Having said that I know motorised focusers exist but they're not common.

                              2 of 2 people found this helpful
                                • Re: how to maka a telescope turn with high precision?
                                  peteroakes

                                  I am not sure why you would need to mess with the focus, I thought with the stars so far away it is focused to infinity or there abouts.

                                   

                                  regarding the motors, it sounds a bit like you have a lack of torque. Don't try to micro step too much, over 8 only makes movement sound smoother but adds no accuracy. (A common stepper is only 5% accurate on its primary step and you cant change that, add a heavy load like a telescope and it can easily ignore many of the micro-steps as they have no were near enough torque to move the stepper until they get to near a full step (4:1 or even 2:1)

                                   

                                  What power supply are you using ?, and what motors

                                  2 of 2 people found this helpful
                                • Re: how to maka a telescope turn with high precision?
                                  colporteur

                                  Examine the technology used to move satellite dishes to track birds in orbit or even solar panel arrays to follow the sun to explore some ideas.

                                   

                                  I have difficultly transferring physical movement with mechanical movement. Mechanical movement left to right can result in physical movement of an object up and down. I find it hard to wrap my head around it a lot of the time.

                                   

                                  I found these two practical technologies have developed products to accomplish the simple movement. The other thing is, that the materials are relatively inexpensive if you are experimenting.

                                   

                                  A kit that is great for seeing is believing is the sparkfun pan tilt kit for raspberry pi. https://www.digikey.ca/en/videos/s/sparkfun/pi-zero-w-pan-tilt-camera-kit

                                   

                                  I have assembled it and found I was exposed to concepts I wasn't able to visualize. It is not to pricey and rather cool to show friends especially if you complete the project and run the camera through a web page.

                                   

                                  If you are interested, drop me an email and I can share some additional resources. I was compensated by a magazine publishers for providing a installation and review so I am unable to post those details in a public forum. I would bend the rules and share them privately if they are use.

                                   

                                  Sean

                                  1 of 1 people found this helpful