Jump to content

Banner.jpg.b83b14cd4142fe10848741bb2a14c66b.jpg

Motor for equatorial platform

Tim Armes

By Tim Armes
in DIY Astronomer

Recommended Posts

Tim Armes

Tim Armes

Posted
Posted

Hi,

I'm about to embark on a project to make myself an equatorial mount for my Dob. I'm trying to find out what options would be available for me with regards to the motor. Can any suggest any decent options bearing the following in mind:

  • I know nothing about electronics, so I'm not interested to buying a bear motor and trying to make my own controller.
  • In a perfect world, it would be a stepper motor with a adjustable speed. None of those that I've seen can be finely adjusted, they just ofter a fixed speed with x2 and x8 acceleration.
  • It should have an axle that I can use to drive a bearing. There's not much I can do with just a cog that sticks out.
  • It should really be designed for this sort of use due to the very slow rotations speeds. Gearboxes are an added expense that I don't need...

The one that I've seen suggested before is the Celestron Logic. It's not a stepper but other than that it seems like a reasonable option. There's also a Skywatcher one that looks similar:

http://www.teleskop-express.de/shop/product_info.php/info/p394_Skywatcher-Tracking-Motor-for-EQ-1.html

Apparently the Celestron version has a bushing attached to the axel that's convenient for my purposes. Can anyone tell me if this Skywatcher motor also has one?

The big disadvantage of these is the 9v battery. I'd rather use a set of AA so that I can recharge them.

Are there other options that I'm missing?

Regards,

Tim

Link to comment
Share on other sites
Mike73

Mike73

Posted
Posted

Hi Tim

To be honest I haven't used it enough to know about battery life because of the light evenings but the motor is very quiet, I can only just about here it running when I'm at the EP.

It also has a fully adjustable speed control.

Mike

Link to comment
Share on other sites
AstroTux

AstroTux

Posted
Posted

The motor in your pictures is the same motor that Celestron supply for their lower priced mounts ( such as my Astromaster 130 EQ ). This is not a very powerful beast and I find that it suffers a lot from varying battery voltage due to the temperature of the air in which you are observing; colder nights affect the internal resistance of the battery, so the motor runs more slowly. One way I have found of getting over this is to use a mains powered 9V DC adapter, but this is not an option when observing away from home.

Also, this motor is also not very easy to adjust to a specified rate - a lot of guesswork is needed and you will find that you are constantly tweaking it. For visual work this is OK but for anything else it will cause problems very quickly.

It is not very loud, but the constant whine of the gearbox can get on the nerves at times, although the battery life is reasonable.

Bear in mind that most motors will require a gearbox. Small motors ( like this one ) need to run fast to develop much torque, so to move a mount at the required speed the gearbox reduces the speed of the spindle and increases the available torque.

It is because of the limitations of this motor that I have developed my own tracking and focussing system using two stepper motors pulled from an old inkjet printer, but as you say that you are not into electronics then I guess this is not the route for you.

By the way, if you are looking to use a stepper motor, be aware that unless you use a gearbox or microstep the motor you could run into the problem of the step motion of the motor being visible through your scope.

Hope this helps.............. :laugh:

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

When I first started astronomy I had a Celestron 130 EQ with this motor on the mount. I soon replaced it with a motor of my own. The problems of adjusting the speed with the tiny knob and keeping it right plus the fact that there was no way of disengaging the motor to slew quickly made it useless IMO. Mine ran off a 12v PSU from the mains, had fast forward and reverse and a regulated low speed for sidereal tracking. I was going to add Lunar tracking speed too but upgraded to a proper mount before I got round to it.

Link to comment
Share on other sites
Moonshane

Moonshane

Posted
Posted

I bought a 4 rpm 12v DC high torque motor and a PWM controller off ebay for mine. works a treat and is very quiet. total cost about £20. I can link to my build thread if it will help. That TS one shown by John is a pretty design. might try one like that. for me though the 'sticky out' motor is a disaster waiting to happen.

Link to comment
Share on other sites
  • 9 months later...
Moonshane

Moonshane

Posted
Posted

Hi Tag

My build thread is herehttp://stargazerslounge.com/topic/88506-equatorial-platform-for-dobsonian-telescopes/ in case it helps. This was the PWM controller I bought http://cgi.ebay.co.uk/12V-15A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller_W0QQitemZ220646588997QQcategoryZ71394QQcmdZViewItemQQ_trksidZp5197.m7QQ_trkparmsZalgo%3DLVI%26itu%3DUCI%26otn%3D4%26po%3DLVI%26ps%3D63%26clkid%3D7229103753728367194

I also bought the motors from ebay. cannot find a link but they were described as

Specifications:

* Torque: 250 N*cm

* 12V DC

* 4RPM

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.