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Home / Upgrading SkyWatcher EQ-4 Dual Axis Motor Drives
by Denis Grey 09/11/03 | Email Author

For owners of Great Polaris and similar CG-5 and EQ-4 mounts there is a key economic decision that must be made. Do you buy the cheap Chinese motor drives or do you buy the expensive (but better) Vixen equivalents? Here is a rundown on the differences between the basic Dual-Axis systems:

SkyWatcher / Synta

Dimension

Vixen

$175 - $240 Cdn

Cost

$665.00

2X / 4X / 8X Sidereal

Performance

Up to 32X Sidereal

RJ45 Telephone

Connectors

Heavy-duty Microphone

Non-standard 6V

Power Supply

Standard 12V

Included

Clutches

Extra-cost Item

Minimized

Backlash

Noticeable

Here is a quote from Joe O’Neil’s website on these drives:

“For the money these motor drives cannot be beat. These units sell for about 1/3rd the price of what I can sell a similar Vixen set of motor drives and clutches for but they have three weakness compared to the Vixen motor drive set. First, maximum slew rate is 8X, while for example Vixen motor drive set slew at 16X and 32X. Secondly, I find the Vixen drives are more responsive at the hand controller paddle. Finally, Vixen uses heavy-duty microphone jacks as connectors, whereas Synta uses light duty RJ-45 (telephone jack) connectors, which just cry out to be snapped off if you bump into them.

Still, at 33% of the cost of a Vixen set, you cannot beat them, as long as you are aware of their drawbacks. Also the motor drive set for the EQ4/5 mount WILL work on the Vixen GP and GP-DX mounts, as I have used them myself on these mounts.”

The slew rate problem is not as bad as it seems since the Synta drives include clutches that allow you to make moderate adjustments in RA & DEC without using the motor. This is a really helpful feature. However, Joe is quite right about the telephone jack connectors which look and feel very fragile. On the RA drive this connector is hidden (and made difficult to access) by the RA motor cover, on the DEC drive it is “right out there” and it is just a matter of time before it is damaged. Fortunately, the rest of the motor unit is fairly robust in construction.

My problem with the connectors (one is too exposed the other too inaccessible) is made worse by my need to make the mount easily transportable. This means tossing it into the car quickly and easily while protecting it from other luggage and the elements. I have customized a toolcase that allows me to pack the entire EQ head and other components for transport as shown above:

Living in Canada’s light pollution capital portability to get to dark sky sites is critical. When packing down the GP mount for transportation several additional problems surface. One is that when the Synta DEC drive is attached it prevents the EQ head from rotating completely and packing down into a compact format. It can be removed but an Allen key is needed which is difficult to maniputate in the dark. The other problem is that the wiring from the hand controller. There are a total of three cables (RA, DEC and power) that are individually wired to the hand controller. This makes a mess of wires when packing it down. They are also long flat cables that can and will allow the fragile hand controller box to hit the ground if dropped accidentally.

So, to enhance my EQ drive set here is what I wanted:

  1. To provide a quick release mechanism for the DEC drive to allow it to be mounted and unmounted easily so the mount head can be packed away.
  2. To replace the “exposed” RJ-45 jack with a protected jack that could also handle being packed away regularly.
  3. To replace the dual RJ-45 cables from the hand controller with a single coiled cable that could be easily disconnected from the mount leaving me with an easier to pack unit. By using a coiled cable with some “bounce” I hoped to be able to prevent the hand controller from hitting the ground. While doing this I also planned to replace the separate DEC cable running from the hand controller to the motor with a relay cable running from the RA drive housing to the DEC motor. This would allow me to replace a 4-foot cable with a 1-foot cable and eliminate tangle problems.
  4. To replace the separate power cable with an integrated cable combined with the hand controller cable that would allow the power supply to be hooked up to the mount rather than to the hand controller.

DEC Drive Quick Release Mechanism

The DEC Drive Quick Release turned out to be very simple. The Synta drive uses a metric threaded bolt that is just a bit smaller than the North American ¼-20 standard. To adapt the mount all that is required is to tap the existing hole with a ¼-20 thread and voila you have a quick release, no tools solution. See photo below:

DEC Drive Connector

The next step was to replace the standard DEC drive connector that was exposed and begging to be broken off. I was able to find a British to North American plug adaptor at a surplus store (also available at Radio Shack and other suppliers). These adaptors have the four wires from the RJ-45 jack exposed inside a small but roomy plastic casing. To adapt it I trimmed off the adaptor plugs from the bottom and soldered the wires together and insulated each one with electrical tape. The casing fits nicely onto the side of the DEC drive as shown in the picture and the wires all fit in easily.

The top portion (with the RJ-45 connector) is attached from the bottom by a screw that comes up from below. I also used hot glue to secure the bottom portion to the motor housing.

Note that it is very important to trace the wires carefully. Make detailed notes before starting or you may have to try 24 different combinations to get it right again!

The finalized unit is shown below:

New Controller Connection

The three cables (RA, DEC and power) require a total of 10 wires to run from the hand controller to the mount.

In searching through electronic surplus stores I came across just the thing – an old cellular phone connector with a CAT 5 connection (8 wires) and a shielded antenna cable (2 wires) on one end and 10 bare wires on the other. The beauty of this is that the power cable can be plugged in separately from the RA and DEC connection while still providing a single cable from the controller to the mount.

The other component that was needed as a Junction Box to allow the combined RA and DEC cable to branch out separately to the RA and DEC motors. This was constructed from two surface jack outlets (one for a standard RJ-45 jack and another for a CAT-5 jack) that were combined and attached to the outside of the RA housing. The schematic below shows the changes needed to the wiring and connections.


Once completed here are the benefits of this retrofit:

  1. The jack for the RA motor is now combined with the DEC motor and surface mounted for ease of access when packing down the unit. Before it was hidden inside the RA housing and difficult to access unless the housing was removed.
  2. The DC power source is now connected to the RA housing and relayed to the Hand Controller. This means that the power source cable is not moving with the hand controller and is less likely to become entangled or stepped on.
  3. The unit can now be operated with the RA motor only (single axis mode) without having the DEC cable hanging uselessly in the way.

Here is a picture of the finished product:

Summary

This is a very worthwhile upgrade that “cleans up” the standard Synta package very nicely. Interested users may wish to do some or all of the steps outlined above. Benefits can be obtained with each step for improved ease and portability.

Feel free to contact me for additional information.

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