Mounting the RoboFocus RF-3 Unit on the LX-200/400 MicroFocuser

The RoboFocus unit can be mounted on the Meade MicroFocuser, commonly found on the LX-200/400 series. The RF folks point to this URL as a guide

http://www.rc-astro/equipment/focuser/index.htm These instructions (referred to below as “the URL” are not quite right for several reasons. The following instructions should get you through to a successful installation.

Before you start The RF-3 unit sold by RF does not need any modifications to the motor, as mentioned in the above link. When you order, be sure to tell them that you’re doing a modification of a Meade MicroFocuser. They will include a coupler to attach the motor to the focuser’s drive shaft. You will not use this coupler in the final installation but let them send it anyway since you can use it to help determine where to drill a hole in the focuser housing. The motor shaft on the RF unit has a hole that is just the size of the focuser’s drive shaft. This is why you don’t need the coupler for the final installation.

What You’ll Need 1. Small Phillips head screw-driver

2. Hex wrenches: 0.05”, 1/16”, and 3/32” (maybe 7/64”).

3. A drill. I do not recommend using a hand drill. Use a drill press (floor or stand) if at all possible.

4. Drill bits. I highly recommend a Forstner-type bit (1/2” or 5/8”) for drilling the final hole.

5. Double-sided foam tape, e.g., that used for putting up plastic over windows or mounting pictures. It’s about 1/10” thick. This is what’s recommended. I found it didn’t do so well. While the pictures below show using the tape, I finally decided on small squares of industrial strength Velcro pads.

Modifying the Focuser DISCLAIMER. THESE INSTRUCTIONS ARE PROVIDED “AS-IS”. YOU TAKE FULL RESPONSIBILITY FOR WHAT HAPPENS TO YOUR ROBOFOCUS, MICROFOCUSER, AND/OR YOURSELF AS OF A RESULT OF ATTEMPTING TO MAKE THE MODIFICATIONS. Please read through the entire set of instructions before you begin. Don’t you just love it when you go through a set of instructions step-by-step and do something, only to find that the paragraph on the next page says something like, “before you do all that, be sure to….”?

1. Remove the front cover of the focuser by removing two Phillips head screws and two allen screws (3/32” or 7/64”).

2. Remove the back cover by undoing the two allen head screws. The instructions in the URL say not to remove this cover. However, it will be difficult to remove the bottom gear if you do not. You may be able to pry it out but there is a good risk of damaging one of the screw mounts if you do not remove the back cover.

3. Remove the top gear by loosening the allen screw on its collar (0.05”).

4. Remove the bottom gear by loosening the allen screw on its collar (1/16”).

5. Remove the small bracket from the large aluminum block. This is held on with two small Phillips head screws.

6. Remove the motor from the microfocuser (it’s the top piece with the wires attached that had the small gear).

7. Attach the RF coupler to the motor shaft. This is temporary and is to help you determine where to drill the hole. Be sure to slide the coupler all the way on so that it’s touching the aluminum block. The coupler has a bushing at one end. You want to put the other end against the aluminum block.

8. Attach the back cover of the focuser by screwing the two allen head screws into the aluminum block. You may have to rotate the focuser drive shaft with coupler so that the lock screws on the coupler don’t hit the mounting stub in the focuser.

9. The back cover will just fit since the coupler is almost too long and definitely too fat. In fact, you may not be able to get the back cover on without using a little force to get at least one of the allen screws into the aluminum block.

10. Do your best to estimate where the center of the coupler hole is in reference to the focuser back in the left-right direction in the picture above. Do not use the center of the coupler hole to determine the top-bottom direction, i.e., the distance from the edge of the back cover.

Without both sides attached, the back side can flex and so you cannot really tell just how deep into the back cover that you want to center the (minimum) 1/2” hole, which is required because of the flange on the motor housing. The hole ended up being split about 60/40 (favoring the back cover) during my four attempts.

11. After several attempts, all with the center of the hole too close to the edge of the back cover, I assumed 5/32” for the distance from the edge of the back to cover to the center of the hole.

12. Mark the center of the hole on the back cover clearly so that you can see it when drilling.

13. Remove the coupler.

14. Reattach both covers completely, i.e., all screws. If you don’t, then when you drill the hole, the covers may try to separate (as they did the first time I tried and so a lesson learned).

15. Use a 1/2" (or 5/8”) Forstner drill bit to drill the hole in the focuser housing. Because of my “luck”, I finally used a 5/8” bit to allow for a slight miscalculation of where the center of the hole should be. The first three attempts could have used this idea. By the time I go to the fourth try and figured out how to really determine the center of the hole, I could have used the 1/2” bit. The slightly larger hole is not going to hurt.

16. Remove the front cover of the focuser. Blow out any plastic shards or dust.

17. Try to slip the RF shaft onto the focuser shaft to check the alignment of the flange on the RF housing to the hole in the focuser. It can be a tight fit so go carefully and only so far to determine that the flange will fit into the hole (the 5/8” hole pretty much assures this if you were reasonably careful with measuring and drilling).

If the fit is a little too tight, try hand-twisting an 11/64” bit into the hole to ream it a little. You don’t want the fit too loose.

A good way to test if the fit is right is after slipping the RF shaft at least part way on, try moving the focuser manually by pressing on the sliding collar (seen on the inside of the opening in the bottom left of the picture below) while holding onto the motor. If you can push with a good force, more than the weight of what’s going to go on the back, and the focuser collar doesn’t move, then the fit is good enough.

If the fit is too loose or you want to be sure, you can use LockTite or some other adhesive of your liking. Don’t use the LockTite that requires you heat things up to 450F for 5 minutes. You’ll probably melt everything in sight. Instead, use something that can be dissolved (e.g., with acetone).

18. Remove the RF motor from the focuser shaft.

19. Attach both covers to the focuser using all four allen head and Phillips screws.

20. Apply the double-sided sticky tape to the RF housing. I used two layers. Note that the URL instructions say to do this after putting things together. That’s because the motor shaft was soldered to the focuser shaft with a coupler and so it was not possible to adjust things later. You’ll find it much easier to apply the tape before final installation.

I found the double-sided tape didn’t stick very well so I used small industrial strength Velcro pads.

1. Cut or pads or strips about 1” square of both sides of the Velcro.

2. Peel off the anti-stick cover of one of the pads and attach it to the RF housing in the same place as shown for the sticky tape in the picture above.

3. Peel off the anti-stick cover on the other half of the Velcro pair and attach it to the other half. Do not attach the second half to the focuser housing.

21. Slip the RF shaft onto the focuser shaft, aligning the motor as you do so that it’s in the right position before the sticky tape (or Velcro) hits the focuser housing. Press the motor tightly against the focuser housing so that the sticky tape (or Velcro) attaches firmly to the housing.

22. Attach the focuser to the telescope (see next page).

In the picture to the left, the RF unit is such that the DB-9 connector is pointing down, meaning that the cable from the RF controller would be coming up from the bottom. Instead, rotate the focuser so that the DB-9 connector is pointing up. The reason is that there are no mounting hole on the connector for the screws on the cable. Therefore, if the cable were attached from the bottom, gravity might work against you and the connector fall off. Of course, you can use other means to assure the cable stays connected if circumstances require the cable come up from the bottom.

RoboFocus Setup These are the steps I used to setup the RoboFocuser. They seemed to work for me. They are slightly different from those in the RF docs and are offered “as-is” and without any guarantee that they will work for you. In the end, getting things set so that all the way IN has an absolute position of 2 and all the way OUT is ~3400 (assuming you use Step Size = 1) is your responsibility.

1. Install the RoboFocus program (in the RoboFocus folder on the CD that comes with the RF unit). Do not start the program at this time.

2. Make sure the RF unit is turned on and the cables between the PC and controller and RF motor and controller are attached.

3. Determine which COM port the RF unit will use. Start by using the Control Panel | System | Hardware utility to determine which COM ports are available on your machine. If you have several and you’re not sure which one the RF unit will be using, don’t worry; the next few steps will determine it for you.

4. Start the RF program.

5. Click on the Config button

6. Click the Adjust COM port settings button

7. Select a COM port from the drop down list and then click the Open Port button.

8. If you selected the right port, you’ll see one of the buttons on the main RF program turn green. Skip to step 10.

9. If the connection attempt was not successful, you’ll see a message about RF not responding. Wait a few seconds until another message appears about the port being closed. Repeat selecting a COM port using a different port each time until you get a connection.

10. Using the controller, push the OUT button until the focuser is all the way out or very close to it. If you go too far, the focuser stops moving, push the IN button and let the focuser go in a very small amount.

11. On the Configuration screen, change the Micro Step Pause to 3 and the Step Size to 1. Do this by entering the number in the field and then pressing <Enter> or tabbing to another field. Duty cycle should be 0%.

The following is a variation on the Manual Motion Calibration described in the RF docs. It’s here because when I ran the procedure, the focuser had very jerky motion and/or stalled before getting all the way IN.

12. Read all the remaining steps before taking any action.

13. Turn off the controller. Do not disconnect from the program.

14. Wait at least ten seconds.

15. Press the IN button and then turn on the controller. It will start beeping (5 times). Release the IN button before the last beep. The focuser will try to move in. On 3 of the 4 units, the motor was noisy, motion was jerky, and the focuser would not go all the way in.

16. Instead of waiting to see if the focuser will go all the way in, wait a couple of seconds after the focuser tries to start moving and then press either the IN or OUT button to stop the calibration.

17. Using the controller (not the program), press the IN button and move the focuser all the way in or very close to it. If you over shoot, use the OUT button to back out a very small amount.

18. At this point, the focuser unit thinks it’s at absolute position 2, which is what you want.

19. On the Configuration screen of the RF program, set the Maximum Travel to 3400 (enter the value in the field and press <Enter>).

20. Close the Configuration screen.

21. On the RF main program is a field that reports the current position (absolute or relative) and allows you to move the focuser to an absolute position or relative steps. To the right of this field is a button with “A/R”. If the values in the position field are red, then the position is relative. If the value is black, the position is absolute. If relative, the value may be very negative at this point.

22. If necessary, click the A/R button so that the position field characters turn black. The position should be 2.

23. Enter 1700 (without + or –) in the position field and press <Enter>.

24. The focuser should move about half-way out. If so, you are set.

I hope these instructions help. If you have any corrections, please let me know. There are many ways to get this done and you may have a better way. These just happened to work for me.

Good luck! Brian D. Warner Palmer Divide Observatory