ASA DDM85 mount – an affordable direct-drive telescope mount

Interested in details? Just ask – but let me give a short summary: actually, it is near perfect (full stop)

Some impressions from my set-up of this functionally and aesthetically master-piece:

Dec axis side-view

Dec axis, front view, complete USB 2.0 bus and focuser connector

Dec axis, back view, “wireless through-cabling” and additional power and signal connectors

Dec axis, bottom view, thread for counterweight shaft

RA axis, side view

RA axis, top view

RA axis, front view

RA axis, bottom view

RA axis, back view, connectors for everything you need

Altitude adjustment, rock solid, very precise

Altitude adjustment, bottom view

Azimuth adjustment, very precise, simple and solid

Still separated

Pier adapter plate, bottom view, plain to fit your pier adapter

Pier adapter plate, top view, with centering

Pier adapter plate on my pier adapter, fits perfectly

Nice detail: counterweights have clamping rings, no scratches on counterweight shafts

The counterweight shaft, yes – solid again

Dovetail plate, rigid but lightweight

Power cable

Voltages available without additional cabling (fits camera, focuser and torque drives)

More cables inside …

… let’s take a closer look (the box is a USB-to-serial converter, no magic there, but looking nicely)

Fits your 12V add-ons on the Dec axis (no more cables hanging around)

On the pier

Axles’ marriage, simple, precise, easily mountable

Both arrived on the pier

Completed

Cables go through the pier adapter, nothing “hanging”

Ok, some cables though, but just below

Sufficient power: during tracking typical consumption is 0,6 amps;
fast moves 15 deg/sec no peaks above 5,5 amps measured with 32 Kg load, well balanced

The mount even suits small instruments ;-)

As I promised: no hanging cables (in fully operational set-up – this one just for the first rough polar alignment)

BTW, have you noticed the rumble pad – the whole beauty can be controlled via joystick.

A more suitable focal length for testing.

Or do some stacking, the mount won’t mind (just don’t forget to adjust the servo’s parameters to match the new load)

Longer focal lengths are no problem either

The mount is operated by Philipp Keller’s “Autoslew” software (actually acting as an ASCOM driver, so just use your favorite astronomy software on top of it). Autoslew is quite simplistic from an user’s experience view, but all the more uses highly sophisticated algorithms inside. In fact, it’s able to “compute away” any kind of repeatable errors of your set-up. My first 30 minute unguided run using a DSI RC10C, f/7.3, 1854mm (Thanks Rich!) indeed showed a maximum error of 0.41 arc seconds (yes seconds, not minutes …) – professional prospects at an amateur’s hand. But beware: you need a very rigid image train of high quality components. If you don't have them – no problem. The DDM mounts are perfect mates for guiding, e.g. just every other minute.

And – yes, I know the NTM-500, tried it, and consider to use one for my very heavy instrument due to its elaborated brake system (something that’s missing from the DDM85 and even the DDM160). But do not get me wrong with this: The DDM’s operation is very safe even without special brakes. When the mount / your instrument bumps into the pier, your head ;-), or whatever it instantaneously powers down the motors not leaving even scratches on your equipment. What you MUST do is to balance the mount’s load very carefully. Again, balancing is very easy due to the “feeling” you get with the “freely swinging” axles and the assistance by Autoslew’s current monitor. Thus you can’t do this wrong or even sub-optimal, even without any experience.

And – yes, I like to use the “el Capitan” also. Just get the extra encoder and feel free to stay with high precision gears. But beware, you might miss a once-in-a-lifetime experience ;-)