Equatorial Platform
My platform is a fairly standard vertical north sector (VNS) equatorial platform, so I won't say too much about it. I built it for 45 degrees (I'm at close to 43.5) for simplicity. The two most notable features are:
- It is a stand-alone platform, but bolts to the bottom of my scope. [The scope feet fit into three snug-fit holes in the platform rocker plate and a couple of eyebolts secure it to threaded inserts in the underside of the scope ground board.]
- The top and bottom halves are connected so that the platform can be carried as one piece. This doesn't interfere with tracking, so I don't have to loosen any locking pins, etc. before use. This system involves a long piece of aluminium angle on the topside of the platform ground board on the North face (first picture below) with an arc cut into it. A shorter length of angle on the underside of the top rocker plate is tapped for a small bolt which passes through this arc and holds the two halves together at the North end of the platform. The bolt can easily be undone by hand to quickly separate the boards. At the South end, a length of metal with oversized holes is held loosely in place by a screw on the top and bottom plates (third picture below). This is actually an IKEA spanner I found lying around, with a washer to reduce the hole size on the ground board.
These facts together mean that my scope can be carried around with its integrated platform, so I don't have to make any extra trips or try to place the two halves of the platform together outside.
The hand controller is the box on the left. I used the standard Q109 kit. The
whole kit including the battery is mounted in the box. This makes
it easy to include double-speed and pause switches, and a speed
adjustor. The LEDs give a visible indication of the speed and if
the circuit is operating (useful for telling if the batteries are
dying).
This box
has a 9V battery compartment. An RJ-something-or-other (6 lead
phone-type) jack on the hand contoller connects to a similar box
on the platform base (last
picture above) which is connected directly to the LSG35 Hurst
stepper motor. I spent a long time looking for a suitable surplus
stepper motor, but the market seems to have dried up so I had to
buy this one new. Hurst won't ship to Canada unless you want to
order 25 motors(!) so I bought this one from electrosales
and they went out of their way to help me. Note the red and black
wires leading up to the hand controller. These supply power to the
hand controller. I can switch the 9V battery for the battery snap
on the end of these wires. If you try this, remember you need to
swap the polarity of the connector. I didn't and blew up the
previous version of my circuit!
The most expensive item I had to buy for my platform (aside from the CDN$90ish stepper motor) was the length of aluminium angle used for various brackets. I had to buy 3ft of it from Home Depot. This actually turned out to be really useful and I ended up using the whole lot up in several places on my scope, including the focuser board and altitude bearings. Other than that and the electronic components, the cost was relatively modest and I already had a lot of the wood left over from building my scope. The bearings I found at a local surplus store – they might be quite expensive new. Same for the rubber drive cylinder.
Some construction notes
I had started working out how to calculate the necessary dimensions when I found an excellent treatment by Gene Baraff who had thought about this in much more detail than I was planning to do. His method can be found in the files section of the eqplatforms Yahoo group, which is the best resource if you are thinking about building a platform.
The elaborate jig for grinding the sectors is shown in the photo to
the left. I'm lucky enough to have a friend who is a local cabinet
maker and he kindly lent me his workshop and assistance to build this.
The jig
involves bits of a sawhorse clamped to a table under his drill press.
After rough shaping the sectors (made of red oak) using an angle
grinder, the platform was bolted to this jig and then passed across a
drum sander in the drill press. The jig was then turned upside down
to do the other sector.