Beginning with the motorisation let’s say that every telescope maker knows that when u move a telescope there are two situations:
Slewing to find an object and then tracking an object on the sky, so when you make a homemade telescope on the motorisation process you will need high speed for slewing and low speed for tracking or fine movements. I like the old way of using stepper motors and other stuff introduced years ago by Mel Bartels, he is a master for me.
My first motorisation was very bulky, then my second built years ago use a ChipKit Max 32 to move 3 motors at the same time, one for azimuth, one for altitude and another for the focuser, all reading an old analog gamepad signal to control them and to activate some accessories like the primary mirror fan, the red light, the mirror heater and of course my favourite, the green laser pointer!
So this is about the 4th motorisation of my telescope, with the cheap components you can find on eBay on these days you can easily motorise almost anything you want. So I purchase 3 x "CNC Router 1 Axis Controller Stepper Motor Drivers TB6560 3A driver board B1" from eBay for about $6 each one.
The other feature that I always like is to use a normal gamepad to move the telescope manually, and not having to build it. So in this case I decide to use a Play Station 2 wireless gamepad (the Logitech one). You can buy a cheap chinese wireless gamepad (for about $10 on eBay). This is the source: http://www.ebay.com/itm/CNC-Router-1-Axis-Controll...
For the power source you can choose between 2 x 12v batteries in series or a 24v CNC power supply depending on your needs.
I cannot get the PS2 gamepad to work with the Max32 board so I decide to use an Arduino Uno to read the PS2 gamepad and connect it to a new Arduino Due using I2C that will send signals to the TB6560 drivers. I need one 32bits board to move 3 motors in real time because normal Arduinos are just capable to move one motor at the same time without losing performance.
The gamepad functions map is shown on the picture.
Step 1: Hack the Stepper Drivers
The TB6560 stepper Motor Drivers have an input for the Enable function, so I decide to change that to obtain micro-step mode and full step mode so u can switch mode with just 1 press of a button and get the low speed mode using 1/16 micro-step mode for tracking and full step for slewing.
First you need to destroy the line on the printed circuit to avoid the enable signal… then connect the enable pin on the TB6560 chip directly to a Vcc pin, so the driver will be always enabled, but don’t worry in the final setup u can add start buttons from the power supply to activate each motor separately.
Now we can redirect the enable input signal to the S4 pin on the TB6560 driver to activate the 1/16 micro-step mode on demand…be sure to test that the old path is not working any more with a continuity test.
Finally, to simplify the connection to the Arduino Due I joint the ground pins on the input terminal connector so only four cables will be necessary.
Be sure to apply thermal paste on the heatsink!, many times people in china "forget" to put thermal paste...
Step 2: Connect the PS2 Gamepad
The cheapest way for me to connect the gamepad is to use an old PS2 control extension so you don’t need to destroy anything important.
Use the image for the color code and connections.
Step 3: Program the Arduinos
Using the Bill Porter library (with some little mod) it was easy to read the control and send the signals to the Due board.
So there is a code for the Arduino UNO that will read the gamepad and manage the accessories, and another code is for the Arduino Due to move the motors, you will need a modified version of Bill Porter’s library in order to get all working properly… the modified library and the 2 codes are available in the same file.
The archive also includes a spreadsheet and a .ino file to test the acceleration curve used on the motors, you can use linear acceleration too, but I like more the exponential curve.
Step 4: Put Everything Together and Test
When I was testing a motor one of the drivers pass the way with sparks and smoke! … so I think that maybe I’m doing something good ;). The third motor is not shown here for the same reason and it will take about 2 months to get the replacements from eBay.
See the schematic used to connect everything together and a video of the system working.
The system features acceleration and deceleration avoiding direction changes that will stall the motors, the leds represent the outputs for the accessories in this way:
X ⇒ Primary mirror fan
O ⇒ On board red light
□ ⇒ Primary mirror heater
△ ⇒ Green laser pointer
In my case the green laser pointer can be powered with 5v, the fan and the red light with 12v and the heater directly with 24v, so I make a mosfet driver with 4 channels powered by different power sources, BUT I do not recommend it because it is a lot of work, and my intention here is to reduce the work. Instead of that I recommend purchasing some variable voltage regulators from ebay and a 4 channel relay board or a mosfet board to turn on and off the accessories. Using a 4 channel mosfet board u can use PWM to control the heater on demand... but it is a future improvement by now.
Here are links for the parts that I buy recently:
4 channel mosfet board (100V-30A max):
5 x voltage regulators (1.25-26V adjustable):
Step 5: About Making the Telescope
Well this is not exactly something easy to do, but I will show some procedures to enable anyone to make a telescope like mine... I start on thinking about it around year 2002 and it is not finished yet so you can figure the process...
Ok, the telescope is made in the mayor part of aluminum, so you don't need to worry about rush or get the telescope destroyed by water like too many others that use melamine for example. I use rivets and if possible stainless steel screws for the same reason.
The sizes of the tubes can be obtained by measuring them directly on the Autocad files available on the Cad.rar file, but the mayor part of them are normal 1x1 or 1-3/4x1 aluminum square tubes wide available on glass stores.
Almost anything you want to know about the telescope can be see on the cad files.
Step 6: JB Welding Aluminum...
I discover many years ago by googling that you can weld aluminum with epoxy glue having great results on precision and aesthetics... even better that normal aluminum welding.
The process is based on using internal reinforcements made of scratch aluminum to fix the parts and then just glued them to the internal wall of the aluminum tubes using the epoxy.
JB weld is better because it can give you 40 min to make adjustments before setting up.
To print the templates for the reinforcements I include on the cad files a "impresion.dwg" file so you just need to print the desired template using 1:1 scale on the printer and stick the printed sheet to the aluminum using tape. Then u cut the aluminum using metal scissors, after that make holes on the reinforcement to help the epoxy maintain the parts in place, I make furrows on the internal aluminum surface of the tubes to improve the glue performance.
To force the aluminum to stay in place I use little foam pieces that will act as a spring inside the union.
For T unions I purchase that black plastic end caps and cut the winds, then use some clamps to secure them in place, make 4 holes and put 4 screws.
After gluing the parts u can clean the excess, I prefer to do that when all is hardened.
Step 7: Stepper Mounting
The bearings used here are from old steppers obtained from old printers, also the bearings holders where cutted from steppers stators...
I use normal bicycle aluminum wheels for the worm gears (about 23" for the azimuth and about 17" for altitude, u can measure them on the CAD file to be sure). To make the worm gear I filled the wheels with JB weld epoxy using a 2mx1/2"-20 nylon screw that can be blended for moulding.
The couplings must be the "lovejoy" style used here, I do not recommend the flexible helical ones at all... here is a link for them: http://www.ebay.com/itm/6-35mm-x-6-35-mm-CNC-Flexi...
I recommend using flywheels, the ones here are made of stainless steel, but stepper rotors can be used too.
In this mounting system I use just 1/4-20 bolts, fixed on one side with nylon insert nuts and nylon washers and a spring on the other side. That configuration using phenolic knobs give me the ability to lower and raise the motor assembly and regulate the pressure against the screws.
I use the same end plastic caps filled with epoxy at the end on the 1" tube threaded with a 1/4-20 tap.
Step 8: Primary Mirror Mount
I purchase the 12.5 inch F5 primary mirror years ago from Swayze Optical at a very good price, it seems that will last forever!... very good quality units can be obtained from that men... here is the web page: http://www.swayzeoptical.com/
It is mounted on a 6 floating points system and just glued with regular transparent silicone to a normal adjustable furniture feets.
All the cables you see coming out the edge of the mirror are for powering a heater using nichrome heat wire and a temperature prove to control the heat via PWM from the arduino (not yet completed).
Step 9: Secondary Mirror Mount
The 2.14" inch minor axis secondary mirror is also glued with silicone to an aluminum mount plate that is floating with stainless steel wire using a group of 8 guitar machine head spider tensioners as shown on the pictures.
There are also some heater and sensors for future temperature control.
The electronics in the secondary are powered via the stainless steel wire.
There are room on the back side of the mirror to put a small arduino that will control the temperature to avoid dew.
The guitar machine heads are mounted on small pieces made of very hard wood and black painted.
Step 10: The Base Assembly
The Base assembly is made using 4 bearings to bring complete free movement on the azimuth direction as u can see in the video...
The more complicated part is mounting the bicycle wheel centered with the altitude axis, I remember that I use a printed cad circle to place it on the correct position.
The truss tubes are 5/8 round aluminum tubes covered by black heat-shrink tubing. They are fixed in place using normal bicycle seat clamps... I need to reinforce the 1" aluminum tube inside to support the pressure.
Step 11: About the Axis
Using heavy duty pivot hinges to support the OTA (optical tube assembly) was the greatest achievement, because they make the design very simple.
On the azimuth axis I just use a normal 1/4-20 screw inside a 2 bearings centered on the base.
Step 12: Focuser
Based on the Clement focuser design I made this monster, just because my original idea was to make all the possible parts by myself, but in this case I recommend just to buy a good one, making that focuser is very complicated if you don't have a high precision metal workshop and the final quality just don't worth it... don't misunderstand me I like to use it but I will not make it again.
Step 13: Counterweights
The counterweights can be adjusted by sliding them on an aluminum pieces that I obtain from an old elevator door profile.
Step 14: Handlebars
Of course even using lightweight aluminum as principal material for the construction the telescope will be a heavy monster at the end, so I decide to introduce some handlebars for transportation and 3" wheels.
Step 15: Laser Mod
I take out the battery of the laser pointer body and connect the power cables to a DC power jack obtained from eBay to give the laser a more professional look like u see in the images. of course it is important to let the power button in the "On" position always so the unit can be controlled by the arduino.
Step 16: Cover and Baffle
The cover is just made of tensioned umbrella fabric in the bottom side with a elastic cord and fixed with velcro on the upper side to a very lightweight baffle made of very thin black painted plastic sheets.
Using the cover I can see the "Leo triplet" even with the city light pollution filling the sky, so I think it is a must have for any amateur telescope maker.
Any comment or question is welcome at firstname.lastname@example.org.