Installing Conrad gears in an HEQ5


Required tools

  • Drill press or hand drill
  • 3, 4, 7 and 10mm drill bits and a small end mill (optional)
  • Counter-sink bit
  • Phillips (cross) screwdrivers
  • Allen key set (metric)
  • File
  • Stepped hole cutter
  • Lathe (optional)
  • Several small containers to hold screws and things

Disassembling the HEQ5 for Conrad gear update

  1. Remove the 6 screws from the motor cover.
  2. Remove the motor cover.
  3. Remove the 4 screws from the top cover. If you have previously installed the MCU update then you'll need to remove the connector.
  4. Disconnect the motor connectors from the MCU.
  5. Remove the 4 screws that attach the mounting plate to the mount.
  6. Lift out the motors.
  7. Using a fine scribe pressed against the Synta transmission cover, mark the underside of each mounting plate by drawing a circle showing where the motor was positioned.
  8. Loosen the two set-screws on the brass spur-gear. These are under the gear spaced 90 degrees apart.
  9. Remove the spur gears.
  10. Remove the 2 mounting screws on the plate that holds the motor in place.
  11. Lay aside the mounting plates.
  12. Carefully (they're very cheap screws) using a correct screwdriver remove the three long screws in the top of the transmission.
  13. Remove the transmissions.
  14. Remove the 3 screws from the Synta spacer plate.
  15. Remove the spacer plate.
  16. Remove the pinion gear from each motor.

  


Note
A nice touch from Synta was putting two set screws 90 degrees apart on the spur gears. Scopes like the Meade LXD75 use a single set-screw and many people have had to loosen the screw and turn the gear so that the set-screw is away from the flat on the shaft in order to get any slop out of the gear; as the setscrew just doesn't tighten.

A safe method of removing the pinion

Take a piece of steel channel or bar and open a slot along the center large enough for the motor's output shaft to slide along it. Place the motor in the slot and set the motor into a piece of scrap pipe or across two bricks (or other support). The motor should now be hanging from the pinion. Cut the end off of a small allen key (they're strong) and using a small hammer with very light taps push the shaft down out of the pinion. The pinion will remain on the allen key and the motor will drop. Put a cloth or other pad under the motor if you wish.

Disassembling the Conrad motors

  1. Using a sharply pointed Xacto knife remove the sealant from the 3 screws in the top of the conrad transmission.
  2. Using a correct screwdriver carefully remove the screws.
  3. Lift off the cover and the transmission from the motor.
  4. Remove the pinion gear from the Conrad motor.
  5. Remove the spacer plate from the top of the Conrad motor.
Your motors are now disassembled and you're ready to start some work to adapt the Conrad gears to the Synta motors.

Adapting the Conrad spacer plate

You'll need to have a drill or (preferably) a drill press handy for this. The three motor attachment screws on the Conrad mounting plate are in a slightly different position from those on the Synta plate. Also, the central hole in the Conrad plate is too small for the Synta motor.

From the diagram below you'll see where you have to drill and countersink. The new holes are in red on the diagram.

  1. Using your drill press open the central hole to 10mm. If you have a lathe, measure the protrusion on the top of the Synta motor and open the hole accordingly.
  2. Use a file to remove any metal around the new hole.
  3. Drill three new mounting holes in the Conrad plate.
  4. Place a suitable end mill in your drill press (if you have one) and counter-sink the new holes. If you don't have an end mill then do it carefully with a drill bit. The tops of the screws must be below the level of the top of the spacer plate.
  5. Screw the spacer plates onto the motors using the original Synta screws.
  6. Press the Conrad pinions onto the Synta motors. To do this either chuck a small piece of brass pipe or fitting into your drill press and adjust it until you see that the piece is turning on-center. Then place the motor onto the bed and slowly press the Conrad pinions into place. If you don't have a suitable piece of pipe or a fitting, then just use the chuck (if the fingers are fairly even).
Adapting the mounting plate

The screw holes in the mounting plate are located for the Synta transmission and do not fit the Conrad transmission cover. New holes will have to be drilled and countersunk.

  1. Place the Conrad transmission upside down on the top of the mounting plate. This is so that there is a method of accurately locating the holes.
  2. Place the Conrad transmission cover on the bottom of the mounting plate.
  3. Turn the transmission cover so that it is correctly oriented with the scribed circle you drew during disassembly.
  4. Using a fine marker or scribe, locate the two new mounting holes.
  5. Lay aside the transmission and cover.
  6. Drill and countersink the new holes. The screw heads must be flush with the mounting plate.
  


Spacing for the declination motor

    The declination motor with the Conrad gears actually comes into contact with the bottom of the cutout in the casting. The motor with the original transmissions fit inside the cutout, when modified it is too long by about .100". I made some spacers from bits of old perf-board (.065") and some small washers to lift the motor by .110" to clear the cutout so that the spur-gears could mesh properly.

    Once lifted, the shaft was too long for my fancy red hole covers, so I sealed things up as best I could with paper and masking tape and filed the shaft down. It's easy as the shaft is fairly soft. Just try to keep the filings out of the motor and electronics.



Re-assembling the motors

  1. Screw the Conrad spacer plate onto the Synta motor using the Synta screws.
  2. Place the Conrad transmission in place on the spacer plate.
  3. Place the transmission cover in place.
  4. Place the mounting plate in place centering the motor in the scribed circle.
  5. Look at the orientation of the motor control wires. You'll want these positioned so that the wires are not near the mount casting. The best location is to have the wires coming out of the motor towards the top of the mount. This will keep them out of the way of the polar scope and the mount.
  6. Place and tighten the 3 transmission cover screws.
  7. Place the motor in position on the mounting plate.
  8. Place the two Synta screws and tighten the motor to the mounting plate.
  9. Place the spur gear in place upside down from the original orientation.
  10. Tighten the spur gear set-screws.
Re-installing the motors

With the Conrad gears the total length of the transmission/motor is increased (see the diagram above). On my mount the RA motor went back in place nicely. The declination motor had to be raised slightly so that the bottom of the motor did not make contact with the mount casting. To do this I used four small spacers between the mounting plate and the mount casting. Put a dab of super glue on the mounting plate (just a small dot) to hold them in place then seat the motor. Once the motor is located in the mount you'll have to break these spacers free to put the mounting screws in and properly set the gear meshing (which is why not to use a lot of glue).

  1. Place the motors in the mount feeding the control wires to the back behind the dec axis.
  2. Loosen the spur gear set-screws and adjust the gear up and down so that it is aligned with the driven gear on the worm.
  3. Lightly tighten 2 of the mounting screws. You just want the plate slightly held as you are going to be adjusting the position of the gears.
  4. Adjust the mounting plate so that there is a slight amount of play (.001 or .002) between the driving and the driven gear.
  5. Tighten the mounting plates in place.
  6. Attach the motor control wires.
Adapting the motor cover

The shaft and newly positioned spur gear no longer fit under the motor cover. You'll need to drill or file two holes for the shafts and gear tops to protrude. These can be covered at a later time.

  1. Measure the distance between the center of the shafts of the two spur gears.
  2. Measure the distance between the bottom of the plate and the centre of the driven gear.
  3. Drill a small hole in the motor cover and check your hole locations.
  4. Using a stepped hole cutter in you drill press open the two holes up until they just provide enough space for the spur gear top and shaft to protrude.


Now you are ready to replace the top cover (and connector) and the motor cover. Test your work.

Note
One thing I noticed after the MCU and Conrad gears update.... my scope ran backwards. I had to set the N/Off/S switch to S (southern hemisphere) for it to track correctly. I don't know whether the Conrad gears turn the shaft the opposite way from the Synta gears, but hooking up the mount to the computer and changing the Rotation setting from Original to Reverse seemed to do the trick. I'll research more.


So, was all the trouble and expense worth it? You bet. Here are some charts showing a representative HEQ5 mount's periodic-error curves before and after the upgrades. I think you'll see my point.

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