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:
2X / 4X
/ 8X Sidereal
Up to 32X
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
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.
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:
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
So, to enhance my EQ drive set here is what I wanted:
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.
replace the “exposed” RJ-45 jack with a protected jack that
could also handle being packed away regularly.
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
cable with a 1-foot cable and eliminate tangle problems.
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
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
Once completed here are the benefits of this retrofit:
- 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.
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.
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:
This is a very worthwhile upgrade that “cleans up” the
standard Synta package very nicely. Interested users may wish to do some or
the steps outlined above. Benefits can be obtained with each step for improved
ease and portability.
Feel free to contact me for additional information.