Summary of Contents for Mathis Instruments MI-500
- Page 1 Setup Guide MI-500, MI-750 & MI-1000 Fork Mounts Mathis Instruments www.mathis-instruments.com January, 2016 MI-750/1000 Fork Mount Page 1...
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Page 3: Table Of Contents
Table of Contents Introduction Mount Components Polar Base Base Plate Rocker and Rocker Base Polar Cone Equatorial Forks Telescope Plates Altazimuth Fork Mounts Azimuth Base Altazimuth Fork Electronic Controls Servo II AstroPhysics GTO4 Installation Uncrating the Mount Hardware Base Plate and Pier Rocker Base Fork Hub Fork Arms... - Page 4 Maintenance Lubrication Cleaning Worm Plate PEC Sensor Home Sensors Renishaw Encoders Cold Weather Operation Electronic Damage Technical Support...
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Page 5: Introduction
Only the MI-500 is light enough to be transportable, provided you have sufficient determination and strength. These instructions focus primarily on observatory installations. - Page 6 Page 6...
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Page 7: Mount Components
Mount Components Polar Base Each equatorial fork mount has a polar base as one of the key components. The polar base contains the right ascension axis, the worm gear drive, and the servomotor that provides slewing and tracking to follow celestial objects across the sky. -
Page 8: Base Plate
The base plate and rocker base for the MI-500 and MI-750 mounts are round, whereas the MI-1000 mount has a rectangular base plate and rocker base. -
Page 9: Polar Cone
Rocker and Rocker Base for MI-1000 The rocker-base of the MI-500 and MI-750 mounts has the azimuth adjustment screws on the north side of the base. The MI-1000 mount also has azimuth adjustment screws on the north side of the rectangular rocker base, with the altitude adjustment is on the south end. - Page 10 The polar axis of the mount pass- es through the polar cone. It is supported by a large shielded bear- ing at the top of the cone and a smaller guide bearing at the bottom of the cone. A black anodized nut is threaded onto the end of the polar axis and serves to provide a modest thrust load to the bearing assembly .
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Page 11: Equatorial Forks
Equatorial Forks An equatorial fork assembly consists of the two fork arms, a central hub, and telescope mounting plates. One fork arm, usually on the east side of the mount, houses the declination axis with worm gear drive and servomotor. The gear casing that is attached to the outside of the fork arm contains this declination drive assembly. -
Page 12: Telescope Plates
For mounts with Renishaw encoders, the second arm has a casing that contains the declination encoder ring and the read-head assembly. The two fork arms attach to the central hub, and the hub attaches to the top of the right ascension axis. When attaching the fork arms to the hub or the hub to the polar base, make sure that all surfaces are clean and free from dirt. -
Page 13: Altazimuth Fork Mounts
Altazimuth Fork Mounts An equatorial fork mount uses celestial coordinates and moves along lines of right ascension and declination in the sky. An altazimuth fork mount uses local horizon coordinates, and moves along lines of azimuth and altitide in the sky. One major advantage of altazimuth fork mounts is that they can support a larger payload than an equatorial fork mount. -
Page 14: Azimuth Base
Azimuth Base The altazimuth fork mount has an azimuth base assembly. The lower base plate attaches to the top of the observatory pier. Like the equato- rial polar assembly, the azimuth assembly features a gear casing, which contains the worm gear drive and servomotor. -
Page 15: Electronic Controls Servo
Electronic Controls Servo II Each telescope mount includes a computer control system. The MI-500, MI-750, and MI-1000 mounts are normally supplied with the Servo II computer control from Sidereal Technology. This is the standard computer control package we use with our mounts. - Page 16 The Servo II control features a PEC (periodic error correction) sensor on the RA worm shaft. This sensor records the phase of the worm rotation. Since the phase of the worm is always known, a periodic error profile can be applied to the worm rotation, even after powering down the controller.
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Page 17: Astrophysics Gto4
The GTO4 control requires a regulated 12-18 volt power supply with a mini- mum output of 4 amps. This control can be used with our MI-500 and MI-750 equatorial fork mounts. - Page 18 Page 18...
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Page 19: Installation
Installation Un-crating the Mount Most mounts are shipped by truck freight or by airfreight. Typically, a shipment consists of between two and four containers. We crate the mount components in heavy wooden boxes and secure the parts using wood screws, nuts, and bolts. This ensures that there is no shifting of the parts during transit. -
Page 20: Rocker Base
Rocker Base After the base plate is bolted on the pier, the rocker base is bolted to the base plate. Before placing the rocker base on the base plate, apply a small amount of grease on the mating surfaces. This will permit the rocker base to slide easily on the base plate, facilitating making changes in the azimuth angle of the polar assembly. -
Page 21: Fork Arms
Fork Arm and Fork Hub the declination drive gear positioned on the east side of the mount. For the MI-500 mount, this installation is a two-person job. For the larger mounts, a team of three or four persons will be necessary. -
Page 22: Installing The Telescope
This will require a crane or simliar heavy equipment. This gives you improved control as you move the heavy components in to position. This also provides a measure of safety as you assemble the mount, Installing the Telescope F o r f o r k m o u n t s , t e l e s c o p e p l a t e s a r e u s e d t o a t t a c h t h e o p t i c a l t u b e a s s e m b l y t o t h e f o r k a r m s... - Page 23 This will increase the fork arm separation, allowing you to more easily slide the telescope into the fork. When the telescope is in place, tighten the four bolts to secure the fork arm. Installing the telescope is definitely a team effort. You are likely dealing with a heavy and expensive optical system.
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Page 24: Slip Clutch
Slip Clutch W i t h t h e t e l e s c o p e i n s t a l l e d i n t h e f o r k , y o u s h o u l d a d j u s t the slip clutch on each axis. - Page 25 You can use the slip clutches on the mount to balance the telescope, check the limits of motion on each axis, “sync” the telescope on a known star, or use the telescope in a manual mode for student use. When the telescope is used under computer control, the clutches should be tight.
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Page 27: Adjustments
After making your adjustments, remember to tighten the five rocker base bolts. Note that for the MI-500 mount, one turn of the azimuth screws changes the azimuth angle by about 53 arc minutes, 38 arc minutes on a MI-750 mount, and 41 arc minutes on a MI-1000 mount. -
Page 28: Altitude
Altitude When the mount is shipped, the altitude of the polar assembly is set to the approximate latitude of your observatory. If you have angular measuring tools, you can refine the altitude of the mount to closely match your latitude. Do this before mounting the telescope in the fork. -
Page 29: Balancing The Mount
Each time after making your adjustments, remember to tighten the rocker bolts. On a MI-500 mount, one turn of the altitude screw changes the altitude of the mount by about 24 arc minutes. On the MI-750 mount, the change is 20 arc minutes for each turn of the screw And on a MI-1000 mount each turn of the screw changes the altitude by 19 arc minutes. -
Page 30: Orthogonality Of The Telescope
It is best to leave the east fork arm slightly heavier than the west arm. In this way, when tracking, the worm gear drive is always working uphill against a modest load. To balance the declination axis, you must shift the position of the telescope in the fork assembly. - Page 31 Loosen the clutches of the mount. Position the fork arms so that they are approximately horizontal to the ground. Move the telescope slowly in declination toward the north. Assuming that you have aligned the finder with the main telescope, locate Polaris in the finder scope A cross-hair eyepiece is very helpful here.
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Page 32: Polar Alignment Using Polaris
Polar Alignment Using Polaris For observers in the northern hemisphere, the star Polaris provides a reasonable approximation to the position of the north celestial pole. The current position of Polaris is about two thirds of a degree from the pole. This angle is slowly deceasing and will be less than one half degree in coming centuries. -
Page 33: Polar Alignment By Star Drift
Polar Alignment by Star Drift Accurate polar alignment takes time and patience. It is a process of iteration. The accuracy of the alignment required for imaging is much higher than for visual use. In a permanent observatory, you can improve polar alignment by the star drift method. - Page 34 Page 34...
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Page 35: Maintenance
Maintenance Lubrication The mount parts that need periodic lubrication are the worm gear and the worm. The easiest way to apply new grease is to use an old toothbrush and distribute the grease along the edge of the gear. Make sure that the grease is applied to the inside of the teeth, since that is the contact surface between the worm gear and worm. -
Page 36: Cleaning
Cleaning Cleaning the exterior of the mount is easy and routine. Use an ordinary cleaner such as 409 or Windex. You should not use paint thinner or other strong solvents, since these can penetrate the painted surface. Exterior cleaning is a matter of cosmetics and personal taste. - Page 37 Next to the pressure spring are two “hold down screws”. These cap screws prevent the worm plate from lifting as the plate moves about the pivot pin. These two screws are adjusted to be finger tight. If the screws are too tight, the worm plate becomes fixed, and you defeat the spring action of the worm against the worm gear.
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Page 38: Pec Sensor
PEC Sensor The Servo II control supports a hardware PEC sensor. PEC is short for “periodic error correction”. As the RA worm rotates, a small disk on the end of worm shaft passes through an infrared sensor. A thin slot is cut into the edge of the disk, and when the slot passes through the small opening in the sensor, a signal is generated. -
Page 39: Home Sensors
Home Sensors The Servo II control supports mount homing. Each axis of the mount has a circular disk or annulus that is mounted above the face of the worm gear. A small U-shaped infrared sensor is mounted on a bracket inside the gear casing. The homing disks are attached to the axis of the telescope, so that any motion of the mount, either by the... - Page 40 When the mount and control are first turned on, a command is given to find the zero home position. You have a choice as to which zero position to use: signal to no signal or no signal to signal. The servomotors set the mount in to motion searching for the zero position as measured by the home sensor.
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Page 41: Renishaw Encoders
Renishaw Encoders As an option, your mount may include Renishaw encoders. Using the Servo II control, these encoders are installed on the right ascension and declination axes (or azimuth and altitude axes). A Renishaw encoder consist of an encoder ring and a read-head. - Page 42 A mount moves when servomotors drive the worm and worm gear. Since there is a 2000 count encoder on the servomotor and the worm gears reductions are known, the electronic control knows the changing position of the telescope. With a good mount installation, the accuracy of the telescope position is limited mostly by the motor encoders and the drive gears in the mount.
- Page 43 There is an indicator light on the back surface of the read-head. When the separation is in range, the light will be green. When the read-head is out of range, the indicator light will be red. When the encoders are in use, check that the indicator light is green. If the light is red, you need to adjust the separation between the encoder ring and the read-head.
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Page 44: Cold Weather Operation
Cold Weather Operation The components of the mount and electronics are all made to operate at temperatures near freezing. However, if your observatory is located where temperatures get well below freezing, you may need to take some precautions. The mechanical components are all rated to about 0°F (-18°C). We recommend that you find a way to heat the electronic control. -
Page 45: Technical Support
Technical Support If you have any questions or problems with the setup or the operation of the mount, please feel free to contact us; Address Mathis Instruments: 865 Ackerman Drive Danville, CA 94526 Email support@mathis-instruments.com Phone 1-925-838-1487 1-925-838-0535 Page 45...
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