Sky Commander changes that worked for me

First, I need to say that Sky Engineering has a great Digital Setting Circle (DSC) product called Sky Commander.  I liked enough that I have two - one for my Losmandy German Equatorial Mount (GEM) and another for my Dob mounts.  The Losmandy version was bought from Losmandy with their encoder mounting kit.  When I built the Dobs I decided to also get the Dob mounting kit ($40 at the time without encoders) from Sky Engineering.  After 5+ years using the Sky Commander on the GEM and over a year with the Dob setup I have found a few areas that could be improved, at least for me.  

A Wireless PC to Sky Commander Connection

I liked the connection between the DSC and a notebook PC, but the cable was a pain, especially with the DOB, since the Sky Commander rotated with the Alt axis.  This is, of course, not a design fault, just something that annoys me.

I looked into quite a few options for this.  WiFi, 900Mhz, and Bluetooth were the leaders.  Bluetooth won, mainly because of the low price and power needs.  There is little known Bluetooth profile called SPP, or Serial Port Profile.  This allows PC software, such as The Sky, to talk to the Bluetooth hardware using a serial port.  The problem was that my 6 year old (and used then) notebook didn't have Bluetooth and the Sky Commander wasn't likely to sprout one in the near future either.  At least it wouldn't without some help.

Since the PC did have a USB 1.1 port I went for a USB to Bluetooth dongle.  Specifically the D-Link DTB-120, which sells for about $40 at CompUSA and Radio Shacks in the area.  I've also used models by Linksys, AmbiCom and those built into newer notebook PCs - they all work. The Sky Commander, which only has a serial port was a little more difficult.  For that I decided on a BrainBoxes BL-819 serial to Bluetooth converter from TekGear for about $85 (I was told that the price has gone up quite a bit since then).   This great little device does all of the work and the serial device that it's connected to thinks that it's shoving bits through a wire.  The set-up looks like this:

I wanted to see if there was a less expensive serial to Bluetooth option.   I have been using a CableMax RS-232 to Bluetooth adapter and it has worked well and cost about $50.  The only bump was that the Cablemax and the Brainbox swap the serial  transmit and receive wires.  This can be fixed with a Null serial adapter or you can create a new cable.  Below is the serial cable that I made.

The BL-819 does need an external power supply.  It comes with a wall plug adapter, which is great for testing and setup, but not practical for the rotating Dob in the field (but okay for a GEM mount).  I put together a 4 AA cell NiMh pack that should power the BL-819 for an evening before recharging.  If not I'll swap batteries. The BL-819 takes a 'B' power tip (4.0mm O.D., 1.7mm I.D.) from Radio Shack, if you should to build your own power pack. 

For the Maxx Telescope I made a 12v to 5v regulated power converter using a 7805 IC and three capacitors.  It also passes through 12v for the Sky Commander.  I needed something light weight since it would be mounted on the secondary cage.

I also made a one foot serial cable to connect it to the Sky Commander.  Only pins 2, 3 and 5 are needed on the DB9.  The plan is to have all of the parts except the encoders ride on the tube rings of Griffin.

I've tested this set-up on with The Sky V5 and V6 at 9600 baud, 8, N, 1 with no flow control and level 2 security on the BL-189.  I expect that it would work well with any software that talks to the scope via the serial port.

Newer PCs often have Bluetooth built-in so the DBT-120 wouldn't be needed.  If you have a really old PC that doesn't have a USB port you could get the BrainBoxes BL-830 to connect to the PC's serial port, a USB PCMCIA card and a DBT-120, or is such a thing exists, a PCMCIA Bluetooth card.

The DBT-120 has an official peer-to-peer range of 30 Feet and the BL-819 claims a 30 Meter range.

The wireless connection has been tested now to about 40' while going through two concrete walls.  Since this is further than I usually have the scope from the computer and there should be considerable fewer electronic gizmos around I expect the range to be good enough.  If not, there are other USB/Bluetooth devices with a greater range.  There are a few Bluetooth adapters that have a flip-up antenna and tout a 150 Meter range.

I also tries out an AmbiCom USB/Bluetooth adapter.  Both it and the D-Link use the same WIDCOMM Bluetooth software, but since they renumber it I don't know if it's the same version.  The D-Link has dimmer green LEDS and the AmbiCom uses a bright blue LED.  The Blue LED would be a real problem at a dark-sky star party.


Slipping Pivot Bolt Fix

On the DOB: The pivot bolt slipped against the ground board, not just on my scope, but on three others as well (all built by different people).  The symptom is that you move the scope but the Alt encoder numbers don't change, or seem to slip.  

I ran into this the first night out.  The temporary field fix was to drill a small hole in the large fender washer on the underside of the ground board and epoxy the pivot bolt to the fender washer and smaller washer (see photo below).  This worked, for about two nights.  A more permanent fix was needed.  It was found in the form of a Torque Washer.   A Torque washer is, in this case a stainless steel washer with a square center hole and spikes that dig into the wood to prevent it from twisting.  The square hole fits the square part of a carriage bolt.  The 3/8" x 1-1/2"x carriage bolt screws into the machined Sky Engineering machined part that goes into the telescope's base board replacing the 3/8" bolt that came with the kit.  I intentionally said that the Sky Eng part screws into the bolt because the bolt can no longer turn.  It is IMPORTANT that you use some thread lock when you screw the Sky Engineering part onto the new bolt or the threads will turn and you will be back to where you were.  Stainless torque washers are a somewhat unusual item and the only place that I've found them is McFeeley's

The Sky Eng Dob kit is a good deal and, except for the bolt slipping, works great.  

The original part with the field fix on it.  It worked long enough (with additional epoxy) to get me through the star party.

The Torque washer with the hole for the old lock screw next to it.  Since this is the bottom of the scope no one will see it, but it still looks better.  You can see the hole from the  previous attempt with the washer and wood screw.

The final version used a stainless carriage bolt welded to a stainless torque washer to prevent any motion.    Otherwise if the bolt backs out, even a little, it will move side to side and throw the encoder off.  This has worked for many years.

Other solutions that were discussed were a jam nut on the top of the ground board and one-piece Delrin bolt/washer combo with a loch screw hole in the oversized head.  

Coiled cable between Sky Commander and Encoders on a GEM

The cables that came with the Losmandy were the long straight type used for Dobs so there was quite a bit of coiled up cables lying around.  This was not a design problem, especially since the cables were from a Dob kit and resold by Losmandy, just something that I didn't care for.

The GEM cables were shortened by taking a 25' black coiled phone 4-wire handset cable and cutting it into two parts.  One end of each cable has a RJ-11 end and the other end of each come together into a RJ-45 end.  The end that connects to the RA encoder can be pretty short (on the Losmandy G11 anyway).   The seam on the wore goes into the RJ-11 the same side on both, but it alternates on the RJ-45 end.  Look at your existing cable when you make this and it will make sense.


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