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Remote control Fine Focuser


pete98

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Have to give all the credit to this project to a guy named Joe B.  Saw his video about a year ago, and knew I just had to build one of these. 

https://www.youtube.com/watch?v=gA-wQFrSTGY

While he does a great job of showing what he did, it wasn't a very good job of showing how, so will do my best to show how I built mine.

What I was looking for was a fine focus unit. Something that would allow me to manually rough focus, and finish fine focus with a remote. Wanted a pulley system that had the largest ratio, and yet would slip when I was manually focusing.  Unit had to be small enough so it did not interfere with moving the scope in declination, specifically when trying to point scope at NCP.  Also had to be small enough not to interfere with any equipment (cameras etc.)

The robots are usually available on ebay. First one I got (and one I used) was a little different from Joe's.

58f946b5ba4e7_MiniCuteIRInfaredRemoteControlToyRobot.jpg.947438714d23e732e5ef9b4f95b00761.jpg

 

This one uses a small rechargeable battery vs the 3 button cells. When I first started all of this, assumed I would be de-soldering the IR sensor off the robot, but turned out to much easier than that.

All that really needed to be done to the robot was remove it from it's case, cut the leads going to the robot's motor leaving as much wire as possible, and cutting the leads from the rechargeable battery leaving enough wire on the robot board to solder two wires to. I would imagine if using the same robot Joe used, it would mean having to solder 2 wires to the connection point on the circuit board where the button cell holders connect. I always have 110 power when using the telescope, so rather than try to do a power pack, just found a box mountable DC power jack that would mount to the finished unit.

There was a small resistor attached to the Robot's circuit board that ran in series with one of the motor leads that I decided to leave on. Not sure how much faster my end product would have run should I have decided to remove the resistor.

I got lucky with the first (of 3) servos that I bought. Redcat Racing Tornado S30 Hexfly HX-3CP Standard 60oz Steering Servo

58f9470b0b9bc_RedcatTornadoS30HexflyHX-3CP.jpg.3f32db3ec1daa4978d0a8e0e0430b660.jpg

I am running 4.5v to the robot. Never put a meter to see what the robot was outputting to the motor, but has to be less than 4.5v. The other servos I got, but did not use (MG996R 55g Gear Servo Motor ) will run fine it I hooked them up directly to the ac power adaptor I am using, but would not turn if I connected them to the Robot board. But, they did come with a little gear pack that proved to be invaluable when hooking up the pully to the servo drive gear.

58f947dd544a3_MG996RGearservo.jpg.aa3b9a12b62b4c82afcc13dbac35b1e6.jpg

Adapting the servos turned out pretty easy too. Took out the 4 screws holding the unit together, and dropped the top case cover off. Cut the 3 wires going to the servo board. De-soldered the motor from the circuit board, and discarded the circuit board. No need for the servos potentiometer either. Re-soldered 2 of the 3 wires from the servo connector cable to the motor. No polarity issues here, unless I wanted to make sure when I hit a button on my remote, the motor would rotate a certain way.

58f94ae4d454e_servomotorleads.jpg.51ae5b52be579983b169dce398bd8022.jpg two leads pictured will get attached to the wires from the robots circuit board that originally went to the robot motor

 

Put the top cover back on, and removed the bottom (the gear section) cover off. There is a pin here that has to be removed that stops the servo from turning 360. Seems some pins have to be cut, some pins are just a press fit, and have to be pushed out. Plenty of pics one the web of the servo gears in case someone can't figure out how it all goes back together again. So now I have a servo that turns 360, have the original servo wiring coming out of the servo case, and the other ends of the 2 wires I soldered to the servo motor will get connected to the two leads on the robot circuit board that use to go to the Robot motor.

This is all on a vintage C8. The collar on the back plate of the scope where the focusing knob comes out was a great place to mount the unit. Being limited to what materials I can work with, and not wanting to use wood, I stumbled on a small (5inx7in) plastic cutting board about 3/8th thick for less than 2 dollars. It was easy to cut, and painted up much better than I expected. I didn't have a hole cut bit that gave me the tight fit I wanted, and ended up having to make a slotted collar. The large gear on the focus knob is from the same material.

collar.jpg.aae57016ad4f362662439b88d2a303af.jpg this slips onto collar on back plate that focus knob comes out of. 

 

 

The plastic gear/pully set i got off ebay had the smaller pullies I wanted, but they had axle shaft holes, and I needed something with a spline to attach to the servo gear.  This is where the gear pack that came with the second servo I bought came in handy.  I used the small round gear from the servo gear pack to attach to the servo drive shaft, then super glued the pulley I used to that.

58f948784456b_DIY60KindsofPlasticGeara.jpg.bc0eba35f2d8a947159e5121ea2d9c94.jpg

Finished unit

58f94bb99b963_finished1.thumb.jpg.5e69ec7bccb539eb8542ad06c167bd08.jpg Four screws are holding the servo, two green led's are the Robot's "eyes". and IR sensor is sticking out above the eyes. 

58f954524c1d2_finished4.thumb.jpg.e276430d301b5d0fcee918cd62af6d8e.jpg

 

To show how slow it all turns, put a red dot on the pulley, and this is how much it moves if the remote is held for 3 seconds.

 58f94d54837c7_finished2.thumb.jpg.1d065f80f9b2be66dc6f161201b2cd74.jpg

 

There is enough slip in the unit so manual focusing is easy.  Rubber band does have a tendency to "load up" on one side when manually focusing, so when I let go, focus knob moves back a tad.  But not having an image bounce around when I put my fingers on the focus knob to hit that last few mm of focus is a dream come true.  And while my dslr does not have live view, my Philips webcam does, and being able to just look at the laptop and push buttons on the remote vs reaching over to focus while watching the laptop is great.

 

 

DIY 60 Kinds of Plastic Gear.jpg

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