Posted 06 April 2009 - 05:22 PM
Purchased the Mini Tower in November for our program. My first evaluation was somewhat lukewarm, and favor the Nexstar series. Yesterday I was prompted to re-visit the Mini Tower, so I took it completely apart. What I found surprised me, thought folks on this thread might be interested:
The tapered roller bearing design for BOTH axes is so simple and elegant it is amazing no other manufacturer has come up with this before now (this is 1940s technology). This is a bomb-proof way to carry weight and have smooth motion in both axes for many years to come.
The worm and worm gear design for both axes is pretty good. Both worm gears are manually clutched which is great--however adjusting these "clamping screws" is not trivial, especially the altitude clamp. It desparately needs more leverage and a locking device for those who want to use the mount manually (without the motors or GOTO features), which is something this mount could really excel at.
The nylon gear and motor blocks (which also carry the bronze worms) seem very under-designed and prone to wear. The fact that there is a company advertizing "tune-ups" for this mount speak to the fact that it does and will require "tune-ups" in the future, primarily because of this motor and gearbox design, I believe.
The gearboxes are mated to the worm gears with an ingenious spring design which takes up any play between the worm and worm gear. The nylon block is allowed to pivot and "float", with the spring forcing the worm against the worm gear. Metal stops at each side of the block (which are adjustable, and will probably need to be adjusted after some wear occurs) prevent backlash from left to right motion of the whole block. The nylon bearings for the worm shaft itself, however, seem under-designed and will probably wear with time.
The software has some very nice features, but also is in a growning pain stage. If this company survives, and responds to comments from its users, this is bound to improve with time. Communication with the Mini Tower via the iOptron ASCOM driver I have found frustrating. The Astro-Physics driver seems to work better in some cases. I hope a more complete set of commands will eventually become available. Also, I find the claim of 1 arc minute pointing accuracy, even when painstakingly aligned, some what overly optimistic. 5 arc minutes is more reasonable, but still VERY good for a portable mass produced mount.
The noise and jerkiness of the drive is a real issue. If you are annoyed by squealing and purring noises that seem to be random while observing, this is not the mount for you. If you observe at very high magnifications often, a German Equatorial is probably a better choice anyway.
In summary, the smoothness and durability of the tapered roller bearing design, with adjustable bearing preload available to the user, and the ability to take it apart, clean it, and re-grease it when necessary, all this in a very small and realtively lightweight space, is this mount's most endearing feature. It resembles a high quality surveyor's theodolite in this regard. However, the drives, software, and computer interface have some room for improvement. Also, if the clutches could be locked in a "semi-slip" position and stay there, this mount would rival the smoothest Dobsonian design for an untracked "just push it around and look" mount, and would provide an ideal platform for two small RFTs or a pair of big binoculars.