Considering a barndoor project.

[Doc]

Now that I'm getting a Eos 1000d for xmas and nearly saved up enough for a larger zoom lens i'm thinking about building a Barndoor tracker to sit ontop of my TAL tripod.

I'm going to build an adjustable wedge and the top of the wedge will be the base of the barndoor.

I've got some lovely 3/4" thick baltic pine from a packing case from work.

I'm going to be using a 1 rpm motor but am unsure of what motor to use considering what torque I need to move the barndoor.

I have seen a 230v mains power 1 rpm motor which I could add a on/off switch to but is it strong enough?

http://tinyurl.com/6e6j6s

Or there is a 12v gear motor .

http://www.servocity.com/html/1_rpm_gear_motor.html

Any ideas.

What do you think.

[Jeff RV]

What about a Synchron motor for a Zone valve. Available from most plumbers merchants at around a £10 + or B&Q it even.

http://www.hansen-motor.com/pm-synchron.html

http://www.uk-plumbing.com/honeywell-40002737003-240v-synchron-motor-p-1401.html

Jeff.

[Kaptain Klevtsov]

Have you considered using one of these?

http://tinyurl.com/5cshd4

The motor turns the dial at 1 rev. per day, a mate built a tracking mount out of one in the days before DSLRs. He told me it worked OK for small loads.

Kaptain Klevtsov

[Doc]

Thanks jeff they sound good

KK I'm intrigued.....

Sidereal time = 23h 56m or 1436 min

At 2o teeth per inch = 71.8" circumference or 22.855" Diameter

If we half it = 11.43" which is the measurement from hinge to centre of 1/4" 20 tpi rod.

So a 1 rpm motor will track stars if measurements above are correct.

So Kk if we use a 24 hour rpm motor what will the measurement be instead of 11.43"?

[Kaptain Klevtsov]

So Kk if we use a 24 hour rpm motor what will the measurement be instead of 11.43"?

You just fasten the camera to the disc, so that it rotates once a day. You need to point the axis of the clock at the north celestial pole, but that's the same for all of these.

Oh and be careful using mains power outdoors, use an RCD or something.

Kaptain Klevtsov

[themos]

I would have thought that a digital circuit with a quartz oscillator, frequency dividers driving a stepper motor through a gearbox would be the way to go.

[astro_dt]

I'm building one from the planetary gears from a cordless drill.

I hope to get huge torque from a simple dc motor with a pulse width modulation circuit to control the speed. Just building the prototype, hope to finish it over Christmas. I have put the test jig on my website and I will let you know how I get on.

Cheers

Danny

[Doc]

I would have thought that a digital circuit with a quartz oscillator, frequency dividers driving a stepper motor through a gearbox would be the way to go.

Themos sounds great but way beyond me.

Danny looked at your site impressive. Let me know how you get on.

[themos]

Found this resourcs and, yes, one of the ideas is quartz stabilised stepper.

http://www.awrtech.co.uk/tdsumry.htm

[Kaptain Klevtsov]

The motor setup looks the business Danny, hope it works well for you. The rest of the site looks very interesting too.

Thanks for sharing that.

Kaptain Klevtsov

[glowjet]

Hi Doc

This is one project I have considered making to enable me to take the camera into the field. I have thought of many ways to make it simple in design so the first basic would be a 12V 1rpm motor having a drive shaft of between 4 to 6 mm dia, which should be powerful enough for the job. I would then follow the basic design which is given, using some 9" of 22.855"dia 20T 1/4 Whit threaded rod and a nut which is in turn attached to a disc then according to the designer it should be turned on the shaft at one revolution per minute to match siderial time. My idear was to fit the motor to the assembly using a simple rubber drive disc of matching diameter to the

disc/nut assembly, so the 1rpm rate was achieved. different drive and disc diameters can be calculated to match what materials you have available. Have fun.

John.

[Doc]

Hi Doc

This is one project I have considered making to enable me to take the camera into the field. I have thought of many ways to make it simple in design so the first basic would be a 12V 1rpm motor having a drive shaft of between 4 to 6 mm dia, which should be powerful enough for the job. I would then follow the basic design which is given, using some 9" of 22.855"dia 20T 1/4 Whit threaded rod and a nut which is in turn attached to a disc then according to the designer it should be turned on the shaft at one revolution per minute to match siderial time. My idear was to fit the motor to the assembly using a simple rubber drive disc of matching diameter to the

disc/nut assembly, so the 1rpm rate was achieved. different drive and disc diameters can be calculated to match what materials you have available. Have fun.

John.

This is exactly what I envisaged as well.

I was just wondering if annyone knew what output torque the 1 RPM motor would need.

Have found some cheap 1 RPM Disco ball motors.

[glowjet]

Hi Doc

I have used a number of low voltage and 240 volt reduction motors for various projects, these had drive shafts of 4mm to 6mm/1/4". those of less than 10 rpm were extremely powerful well in excess of that required to drive a threaded disc along a 1/4 screwed rod, most all of these were obtained from Boot Sales and Auto Jumbles for very little outlay. The website for ServoCity already mentioned in a previous thread has, if I remember, a 12volt motor of over a 1000 ounces torque which would be more than adequate. Special attention need to be given to the design of the drive unit, a solid rubber drive wheel of say 12mm thick driven onto a similar size disc of say 5mm steel, threaded for 1/4 whit, would have to have a pressure adjustment mechanism, because any slight alteration in the pressure of the two wheels will have an effect on the final drive speed, this, of course, could work to your advantage, acting as a speed adjuster. You will also need to make some form of bearing surface iether side of where the threaded rod passes through the board which can be kept well greased to reduce friction.

An electric drill in a stand is an advantage when making something like this, a lathe is even better.

Hope I have been of some help.

John.