Computerizing a LightBridge 16”, With LX200 Classic Parts

They say it shouldn't be done. I wondered if it would work too, but found that it can be done, and easier than I thought. And  now, after using it all night for a half dozen nights at home, and packing it up and trucking it to and from dark sky sites 4-5 times, and using it for 10 days down in west Texas at the TSP,  I am ready to call it a keeper. Most importantly, it does what I built if for, GoTo and track. Is that ever nice. As a bonus it has all the capabilities of a Meade LX200. I find it quite a bit more stable than a classic LX200, I'm guessing because the EP is much further from the center of rotation, and it's overall heavier, meaning it is far less bothered by my eye bumping the EP or me otherwise touching it. Here are some data that might be of interest.

1. The motors can generate about 4-5ft/lbs of torque. At the lowest tracking rates, it'll stall around 4. The innovations below reduced that to under 2 at 20 deg F

2. The LB16 OTA weighs about 80lbs incl EP, counter weights, & finder: That load is distributed at 60/20lb at a roughly 18/56” ratio from center of mass. I tested weights up to 106 lbs, divided by weight and distance per above at slew rates up to #4. I was chicken to go higher because it was clear that at that rate the gear system was being strained. The LX200 Classic motors have no ramp start or stop. I found the lowest slew rate (#2, which is also the “Find” rate), to be comfortable. Once the scope is aligned, I remove the finder scope and adjust the counter weight to reduce the mass and momentum. It takes 30 sec to go from horizon to zenith, and 60 sec to rotate 360.

3. Cost $650.00, $500 of which went to the purchase of a complete set of spare parts, just in case, and because this works just too well to want to loose it.

 


I separated the LB lazy susan boards and stuck the LX200 base in btwn, and attached the arm to the LB hub and anchored it to the frame. As a nice surprise, the wheelbarrow handles and wheels fit without any special provision. They go on and off easily with just me doing it.



A 12' telephone hand set cord for the keypad, and a new longer Ethernet cable for the Alt control accommodates the larger system



A detail of the Alt arm connection to the OTA. Note the 3/8” pin in the center of the LB hub going into the center of the LX200 arm. A 10/24 screw is all it takes to connect and drive the hub. It's intentionally a bit light, to serve as shear pin if ever needed. One nice bonus is the clutches of the LX200. If I ever loose the automation, I'd probably leave the mechanics intact because the clutches are so smooth and finely adjustable.



Opposite the Alt cntrl arm I put this adjustable counterweight which allows me to optimize balance for pretty much any EP. Note the permanent counterweights on the back of the can. They minimize the adjustable weight requirement.



The attachment bolts to the base unit. The 2 outermost 1/4”- 20 bolts attach the OTA assembly to the base fram. The two inner ones hold a center pin reinforcing plate on the bottom. And there's a 1/2” centering hole into which the base's centering pin projects



The secret to making the Alt cntrl work is two ball bearings on each shoulder rest. It was the only thing that reduced the friction to where the motors could handle it consistently easily. It was pretty precision placement so that the original bearing material slightly but definitely remained in contact with the OTA hub. Acts as a nice brush that way too.



The heart of it all, and the most expensive parts. The main plate on the bottom of the upper board was needed because the board is unusably irregular, and would never stand up to the omni directional ball roller supports. The weight of the OTA is primarily carried by the angle pieces bolted to the base controller. The ball rollers are stabilizing outriggers, adjustable to a fine level to suit their purpose. Originally I had rubber wheels where the ball rollers now are. They didn't work. There is also necessary bottom board reinforcing.



The bottom of the bottom board. Note the needed reinforcing, bolted through to the LX200 main controller out to the foot levelers