Celestron CI-700 conversion


Alexander Varakin
 

There were not many conversions of this mount so far, so I am sharing what I have done. 
I made brackets out of 3/8" AL which were attached to the RA and DEC plates using pre-existing threaded holes.
The motor plates were made out of 1/8" AL and have holes for the motors as well as aviator plugs.
The plates and brackets were cut using my CNC router, but they can also be easily cut using simpler tools.
The timing gears are 16 and 40 teeth GT2.
I used  MKS Gen L v1 as a controller, TMC2209 drivers and 17hm19-1684s motors.
So far I like this mount - it is fairly lightweight, has an unguided RMS of about 6" at 480" worm period, which is easy to guide out. 
I am getting about 0.8" - 1.0" RMS while guiding. Not great, but ok for an 1100mm scope it is intended for.

Alex


 

Very nice.  Was this mount made by Losmandy?  A G11 equivalent?

I use the MKS 2.0 with TMC2209 drivers.  How fast can you get the GOTO/Slew to go?


Alexander Varakin
 

Thank you Otto!
It is more similar to Celestron CGE than G11. Based on my research, it was designed and built by Celestron, although it seems that there was some influence from Losmandy.
I believe my speed is ~3^/s. The board is very slow for the newer versions of Onstep and can drive mount no faster than 1^/s. The only way for me to get the desired speed was by reducing HAL_MAXRATE_LOWER_LIMIT to 20. Howard does not recommend this, but it works for me with multiple mounts.

Alex


 

On Sun, Oct 17, 2021 at 11:37 PM, Alexander Varakin wrote:

I believe my speed is ~3^/s. The board is very slow for the newer versions of Onstep and can drive mount no faster than 1^/s. The only way for me to get the desired speed was by reducing HAL_MAXRATE_LOWER_LIMIT to 20. Howard does not recommend this, but it works for me with multiple mounts.

Alex
Do you know what the HAL_maxrate_lower_limit parameter does and why Howard opposes adjusting it?


Khalid Baheyeldin
 

On Mon, Oct 18, 2021 at 07:04 AM, Otto wrote:
Do you know what the HAL_maxrate_lower_limit parameter does and why Howard opposes adjusting it?
It is a limit on how fast the microcontroller can pulse the motor, depending on actual testing of each microcontroller.

It should not be changed, since the values in HAL are the ones that are guaranteed to work.
If you lower it (i.e. assume that the microcontroller is faster than it acutally is when running OnStep), then you will see unpredictable results.

So, don't change it. Listen to Howard ...


George Cushing
 

I'd worked on several Nexstar 8 and 11GPS mounts and only lately got my hands on a CGE. Bit surprised to see that the worms and worm wheels were shared by the two mount models. Very likely some of the CI-700 design was shared with GPS and CGE models.

It's fairly clear that Losmandy Had no direct involvement in the CI-700. At least they have officially denied it.

Prior to the Celestron/Losmandy G11, Robt. Byers produced Celestron's worm gear sets. After making 22,000 sets he wasn't interested in continuing the arraignment.


Alexander Varakin
 

Changing HAL_MAXRATE_LOWER_LIMIT is like CPU overclocking - not recommended by vendor, risky, takes time to get it right, but gives a chance of improving performance for free :-)
In case of CPU overclocking, people get all excited if they see 30% improvement, in this case, it is more like 300% improvement.