barn door

[scopemankit (Chris)]

Here is a pic of a perspex barn door mount I finished last week. The circuit shows a lot of diodes. This is to allow me to run on max torque single step. A pic of the pointers 2X2min, iso800 @ 55mm is shown. The diffraction spikes are from wiping the dew off the lens.

There is a semicircular piece of wood nesting in the camera strab which helps minimise the effect of mirror slap on the old 350D The tin on the ground is a new hi-tech lens cover for dark frames.

[rcheshire (Rowland)]

Often overlooked they are under rated, but perform well properly made. Tracking looks good.

[alistairsam]

Looks good Chris.
do you have any close ups of the mount?
I've always wanted to build one. never really understood it though.
what do you think would be the longest exposure you could get with tracking on?
have you thought of using these easy to use stepper boards that do microstepping ?

http://littlebirdelectronics.com/pro...r-motor-driver

http://littlebirdelectronics.com/pro...age-regulators

these drive motors straight. all you need is a 555 oscillator.

[scopemankit (Chris)]

Thanks Rowland & Alistair,
here is are a couple of close-ups.
I have had 5 min on 55mm, fogging is the problem.
A microstepper would be nice but a commercial drivers cost is prohibitive. The total cost of this (excl tripod - and tin) is about US$20.
Sorry about the roll of solder on the front of the angle support.

[naskies (Dave)]

I like your handiwork, Chris!

I recently had a linear actuator (link to data sheet below if you're wondering what they are) and a few Phidgets interface boards (similar to Arduino) left over from an engineering project, and built myself an isosceles barn door tracker.

http://www.firgelli.com/Uploads/L12_datasheet.pdf

The actuator was mounted in between the two planks of wood (opposite the hinge) and I wrote a small script to change the length of the actuator according to the sidereal rate (0.2 mm accuracy).

Upside: ridiculously easy to assemble. Downside: the actuator alone costs $90 USD!

I've since 'upgraded' to an NEQ6 mount

[rcheshire (Rowland)]

Nice workmanship Roger.

I built a double arm drive and used an Arduino board. I think you can get them from HK for about 10-15 AUD.

I wrote the code and made the shield for the electronics. It started out ticking the motor away at 1 rpm. Later I added a 5:1 gearbox and increased the rpm, which was much smoother and provided a big increase in torque - Tamiya hobby planetary gearbox sitting around and pressed that into service.

[scopemankit (Chris)]

Thanks guys, the idea of a linear motor is unusual, to say the least, but good innovation.

FWIW here is a pic of my northern horizon, The bump in the lower right is one of our observatory domes.

To guide, Vega is the star in bottom centre of the pic.

[bojan]

Originally Posted by scopemankit

Thanks guys, the idea of a linear motor is unusual,....

Not quite - what you made is exactly what is in that "linear" motor..
I am sure it is actually conventional motor inside with threaded rod or geared rack & pinion or something similar (with encoder in a form of potentiometer).
http://en.wikipedia.org/wiki/Rack_and_pinion

Your solution is way cheaper, and quite adequate for the purpose (in terms of precision, load capacity and so on).