ETX-90 FOCUSER #1244
Last updated: 31 December 2011
Sent: Sunday, December 25, 2011 22:02:22 From: Wagner Lipnharski (firstname.lastname@example.org) thank you for your website and the pages about Meade ETX, it saved my neck several times. I finally bought the Meade #1244 Focuser for the ETX-90, after testing (for months) the steel cable without so much comfort. After months of torture of the steel cable I finally resolved to remove it for good. It doesn't worth the pain. Recently I was observing Jupiter almost at Zenith (best brightness and less atmosphere complications at this time of the year in Florida), and the ETX setup of Alt/Az is ridiculous for that angle, it simply can't keep up a correct tracking. So, I changed the ETX setup for polar alignment, and also enjoyed astrography of Jupiter. But astrography requires a perfect focus, it was cold (yeah, for Florida) outside at 2:00am and the focus was hard to do, mostly because the SPC-900 camera was showing the image at a notebook inside of the warm room, and I almost needed to be guessing if Jupiter bands were in focus or not, while turning the focus knob outside and watching the notebook over the table inside. Next morning rush to purchase the Meade #1244 focuser online, received next morning. Well, I installed it without even reading the instructions at Meade website. For sure it took me 2 minutes to guess and install, and find the control keys at the #497 AutoStar controller. It was interesting to NOT read the installation instructions, since I could find two things not stated at the documentation (later reading): 1) You can activate/deactivate the arrow keys (#497 controller) for focus, just pressing "0" (zero) at the keypad, other than pressing and hold 2 seconds the key "Mode". Pressing zero is interesting since it also turns on the #497 red led light (for reading maps) at the top of the controller, and it now also indicates the arrow keys are set for the focuser and not to the motors. It was a nice discovery, undocumented. This may be a software update of later version, I updated the software of the #497 in December 2011. 2) I also find out that installing the #1244 without the "boot" helps a bit in the ETX-90. The "boot" is the plastic tick cover that is "necessary" to be installed before the gear, it really closes the focuser gear chamber against dust and other minute debris that may fall inside the chamber. But the "boot" also makes the #1244 to be 4mm taller to the back of the scope, and it WILL RUB against the right arm of the fork. Reading around, Meade says it this rubbing is not "a problem" (but it is, yes, it is a problem). Just set the scope in Polar and try to move the scope smoothly around Polaris... you simply can not, the scope jumps due the friction of the focuser with the arm. The #1244 encasing is a great shame for Meade, it could be designed with minute differences and avoid such mess. Want to increase the problem? Setup Polar (North) and send the scope to look Sirius or Capela when located low Alt at the East. The scope will rotate the base (AZ) CCW while will be trying to move the scope out of the original polar alignment (out of the fork), in that position, the scope weight will bend both arms of the fork 2mm due gravity, and the #1244 encasing with stuck in the arm so hard that the Alt knob will need to be really tight for the Alt motor be able to move the scope. Meade say it is "not a problem"? Okay, installing the #1244 without the boot helps, but cause another problem, dust and debris may enter the #1244 encasing. Okay, a tinny foam in place of the boot may helps, but I don't like it. So yesterday I sand the #1244 encasing. Used two sandpaper grits, a 100 and a 400, and resisting the urge to use the Dremel, I was able to take 1mm (at least) from the whole side of the encasing (the side with the "Meade" text), mostly on the cover and where cover and body of the #1244 encasing touch. I even folded the #400 sandpaper and hold it against the fork arm, and move the scope in and out of 90 degrees, so the #1244 encasing would rub against the sandpaper, so it was easier to see where to remove material. At the end, I apply a little bit of grease at the arm and it "paint" the #1244 encasing, showing me where to remove more material. Well, at the end it DID NOT solve the problem completely, but helped a lot. Shame, shame, shame to Meade for this big design mistake. Anyway, now I can change focus from inside home, fantastic. I have a extension of the #497 cable, and the USB long cable from the SPC-900 camera, I don't even need to be outside anymore. Two tips for the new users of the #1244: a) For the focus sakes, GREASE the #1244 gears. b) The slow speed for the focuser may NOT work, and may NOT even rotates the focus shaft (even if you hear the focuser motor rotating), if you tight much the #1244 installation long screw. As another design mistake, the plastic little pipe that protrudes inside the back of the ETX-90 doesn't go correctly down to the bottom of the hole, also the diameter of the pipe is smaller than the hole, so when applying torque to the screw it may bend (ugly again) the whole #1244 body, taking off the alignment between the #1244 internal bronze gear and the bronze gear at the focus shaft, it may create difficulties to the focuser motor to move the focus in such slow speed, when the motor has not so much torque. Just release a bit the screw and the focus will move in all the speeds, but then, you will be compromising how solid is the connection between the back of the ETX and the internal support. Don't worry, you can survive and still able to see Moon craters. I also read at the internet people saying that when using the handheld controller for the #1244 (the one that comes with the unit and uses the 9V battery), sometimes the focus motor moves when pressing the SPEED center button. I read someone posting an email saying he found out that you need to press the SPEED button right in the center of it, otherwise the focuser motor will rotates. Well, today I opened the focuser handheld and found that it is simply keys, battery and connector, no electronics inside. And more, as the RJ22 connector has only 4 wires, and two are used for power, there is only two for communication with the focuser, but the communication is not digital, is bare switches, so there are only LEFT and RIGHT communication pins. The trick Meade did to inform the focuser to change speed, is just pressing both buttons at once. So, the center button "SPEED" actually presses two contacts at once, each is in parallel with the LEFT and RIGHT buttons. So, pressing LEFT and RIGHT at the same time also will change speed, and, yes, the poster friend is right, if you press the SPEED button not exactly at the center, you will not be pressing both buttons at once, and will be doing exactly the same as if pressing the LEFT or RIGHT button, so, no speed changes and motor runs... ugly, eh? Meade could simple solve this by changing the design at the circuit board to receive three or four contacts under the same single SPEED contact and avoid this misfortune. I already did this in my electronic designs. If I can do, Meade could do too. There is a simply electronic modification that can be done in that controller, but requires a bit of knowledge of using electronic soldering and messing the circuit boards. The idea is cut the little traces from both duplicated Left + Right buttons (under the SPEED key), solder both together and solder two 1N4148 small diodes from both keys now soldered together to each LEFT and RIGHT key contacts, or directly to R2 and R3 resistors. Neat and simple. Now, even if the Speed key presses only one and no both keys underneat, the diodes will send the current to both R2 and R3, as if the Speed key was pressed correctly at the center. I will do it next weekend and post a picture here. Please find attached the electric design of the handheld. Interesting to note that when using its handheld controller, the focuser motor will be only feed power from the 9V battery and through the 1k Ohms resistor R3 or R2, depending of the key pressed. So, this motor is really low power, it never receives more than 9mA of current. Cheers from a Christmas day in Orlando, Florida. Wagner Lipnharski Orlando Florida ETX-90, CPC-800 with 2" kit, Celestron Bino, Dreaming of black skies.
From: richard seymour (email@example.com) In Wagner's excellent diagnosis of the 1244 focuser, he wrote: > Interesting to note that when using its handheld controller, the focuser > motor will be only feed power from the 9V battery and through the 1k > Ohms resistor R3 or R2, depending of the key pressed. So, this motor is > really low power, it never receives more than 9mA of current. That's not correct. The switch signals are being fed to a microcontroller inside the focuser. Thus they are being seen as "logic levels", not motor-driving voltages/currents. (they are pulled "low" by R1 and R4, and pulled "high" by the switch action) The in-focuser microcontroller has an H-bridge circuit (similar to the Alt and Az circuits) which feeds much higher currents to the motor (and makes it reversible). There is another nuance of the 1244 focus system... the 9v battery is *always* powering the in-focuser microcontroller ... and that is why a typical alkaline battery dies in about 4 days if left in the hand control. have fun --dick
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