A battery of tests using the new one piece worm block from Losmandy
Below are a series of tests conducted on my Losmandy G11 mount in June-July 2010 using the new Losmandy one piece worm block. Part of the new block design uses a Ruland disc coupler in place of the original Oldham coupler. Questions arisen in the Yahoo Losmandy users group about the new coupler used in place of the Oldham coupler drew some concerns and speculations. So I decided to do a comparison test and while at it, a McLennan high precision gearbox was used to test against the original Losmandy Gemini gearbox. I also added a another section to test ceramic bearings which have been reported to reduce the infamous 76 sec error. PemPro V2 was used to measure, plot and display performance results in addition to PEC programming.
This series of tests include:
- View of new block assembly and assembly steps.
- Initial performance tests.
- Compare the stock Losmandy Gemini gearbox to the McLennan high precision gearbox using the Oldham and Ruland couplers.
- Compare the stock steel worm bearings with ceramic bearings.
- Discussion on the 76 second error.
- Guider exposure length tests.
Important note on PE measurements.... Due to mechanical changes each time the worm assembly is changed, minor PE differences should be expected. It's impossible to perform work on the block/worm assembly and get the exact PE readings afterwards but possible to get close with minor fine tuning. Other factors such as balance and sky positioning will also effect PE readings. Imaging in the same part of the sky was also done to minimize any possible variable due to equipment load balance.
Before uploading, the PEC profile was modified with a -0.5 sec delay to offset file download and processing times. This setting was found by changing the delay and repeated testing to achieve the best star RMS profile as measured in CCDSoft as well as visual. Your mount will vary with this setting.
I want thank the author of PemPro, Ray Gralak, for helping me interpret the results that verified my findings. A second opinion is always good as a sanity check and what better source than the person who wrote the program.
(Clicking on the images will open a larger version to better see the details)
| New one piece worm block with stock Losmandy Gemini gearbox on left and the McLennan gearbox on the right. Note the Oldham coupler using a custom adapter I made for the gearbox test.
|| VXB ceramic bearings. Shown also are the stock steel bearings that came with the new worm block
Unless mentioned otherwise the following were used for all tests:
- OTA - Deep Sky Instruments 10" R/C 1854 mm F/L @ F/7.3
- Mount - Losmandy G11, Gemini using the new one piece worm block
- Location - Backyard - Abbott Observatory, NY
- SBIG ST-2000XM mono camera
- Image scale - 0.82 arc seconds/pixel (measured at 0.836 arc seconds/pixel)
- PemPro V2 - Evaluate PE data and generate PEC profiles
1- Assembly steps and alignment of new one piece worm block
2- Initial performance of new worm block
3- Gearbox tests using Oldham coupler
4- Gearbox tests using Ruland coupler
5- Ceramic bearings tests
6- 76 second error investigation
7- Guider exposure tests
8- In conclusion