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Some thoughts on EQ platform for a Dob

kernowstargazer

By kernowstargazer
in DIY Astronomer

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SniffTheGlove

SniffTheGlove

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Yes, Building one is easy if you have access to a router.

The most difficult part of the build is getting the segments cut perfectly.

I just went with a single segment and a pivot design (different to Shane's build) and used the same motor/gearbox as shane did after my fancy arduino based stepper motor did not have enough torque to shift 40lbs of scope.

Webcam imaging is OK and stable for at least 15mins on mine before I need to tweak the motor speed.

For a cheap and cheerful build it's great, cost me approx £80 in materials and about 40 of build/tinkering before I got my platform happy.

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kernowstargazer

kernowstargazer

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I just cant seem to get my head round actual shape of the platform and the angle of the top board. I was thinking about some Radio gear, 12v drill motor and a electronic speed controller as i could control the RPM of the motor to match the movement of the object in FOV. Early stages yet as its all still in my head.

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SniffTheGlove

SniffTheGlove

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I just cant seem to get my head round actual shape of the platform and the angle of the top board. I was thinking about some Radio gear, 12v drill motor and a electronic speed controller as i could control the RPM of the motor to match the movement of the object in FOV. Early stages yet as its all still in my head.

Avoid the 12v drill motor, they are clunky and difficult to contol precisely.

This is the place I brought mine from.

A good motor/gearbox is 37mm 12V DC 4RPM Replacement Torque Gear Box Motor | eBay

The speed controller is eBay - The UK's Online Marketplace

This is the easiest way and the motor has plently of torque.

You can view my platform thread for photos (See sig) and look at page 4

What scope are you putting on the platform?

There are plenty of platform designs with plans and dims out there, even in my thread I have a spreadsheet http://stargazerslounge.com/attachments/diy-astronomer/50323d1296755777-build-project-dob-equatorial-platform-eq_platformnssp.xls to do all the calcs for you. If you need help just ask

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kernowstargazer

kernowstargazer

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The drill motor idea came from seeing people build RC crawlers and using 12v drill motors as they were very torquey. I need to use stuff i can scavenge as funds will be low so would like to do a scrap heap challenge type build where all the stuff and materials i get i got for free or very cheap and local. I will be getting a SW150 or 200p dob next week. Cheers for the heads up on your sig and i will be asking questions in the future when my ideas go belly up;)

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bluemarkus

bluemarkus

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hello there. yes a platform will be a very powerful tool for your dob, and cheap to built below 50 pounds if you have a well-stacked workshop. for my 10 GSO dobson (30kg), i used as a drive an EQ-2 motor that i drive with a 12V-adapter instead of the 9V-Block. u dont need a CAD system to cut your segments, u can calculate them, hand draw them to aluminium or hardwood and cut them out with a handsaw. it took me some days to build mine, some more days to cure the little problems i encountered but in the end, tadaaa... u have a tracking dob ! the whole setup will still be a bit shaky so nothing for high-precision astrophotography, but once the tracking speed and angle is correct it might give you also the option to do simple widefield imaging without blurrs.for some planetary work with a webcam it should work, most capture programs nowadays have auto-center function integrated. so you dont have to "push" the dobson for going after your planet and can gather more raw images or bigger AVIs.

i would go for an VNS platform that uses only 2 wheels, its a wee bit more calculation in the beginning but that is time well invested, if u cant do it give your measurements to the forum and let people calculate for you. VNS is definitely more stable and less work and less clumsy.

first i thought i´d need a way bigger motor, but a small motor is enough since u slow it down very much through the gearbox. a motor for rotating disco-spheres as sold on ebay should work as well, but u might need another gearbox to slow it down even more. for speed regulation a PWM (pulse-wave-modulation, as used in dimmers for indoor lighting) is ideal (or a stepper motor + controller if u have the money), if u dont have that try a simple potentiometer in the beginning.

good luck and have fun.

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SniffTheGlove

SniffTheGlove

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Thanks very much i like your dimmer switch idea thats given me pleanty to think about. Ill have to start working things out on paper. Just to clarify whats a VNS platform sorry if its a daft question.

VNS = Vertical North Segment. ie a pivot point

Also if you are going to use a dimmer switch, these are nearly the same price as a proper speed controller. How you do it is up to you but just make sure your chossen dimmer switch will be able to control the motor gearbox to the precission you need and also handle the current you are going to put through it, as the motors out of battery operated drills use a high current to get the torque. The speed controller I quoted before can handle up to 15A.

If you don't have a well stocked workshop then you need to look at some decent suppliers, if you want a good strong platform I suggest 18mm plywood, for the wheels I suggest good hard rubber wheels (you can get these from screwfix) and the softones will deform and this will ruin your angles a bit. To drive your platform I suggest you look at how you will custom mount your drill motor first and work out if it will do the job first on paper, also how are you going to control the platform (ie control gear) ie if you mount all the electronics on the platform this means you have to keep bending down to adjust. I have all my gear in a hand held box so it make life eaiser for me as I trouble with my spine and can not really bend down or squat down to adjust things.

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SniffTheGlove

SniffTheGlove

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Oh my god to much information brain over load coming on:icon_scratch:. I think i will have to work on trial and error and loads of questions:D

OK.

Start of with what scope do you intend to put on the platform. Looking for the weight and also the centre of Gravity of the scope. Once you have these you can start to work on the platform size and load carry capability.

For example my Homebuilt Dob weighs in at 40kg.

Alos look at http://www.reinervogel.net/index_e.html?/Plattform/Plattform_e.html for my answers

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ToxoLight

ToxoLight

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Hi Guys

I've been following this thread and although I havent purchased a scope yet my intention is to go for a SW Skyliner 200p solid tube, in the meantime and before my retirement while I still have access to machines at work I intend to build a VNS platform but to facilitate the calculations required I need to know the centre of gravity for this scope as measured from the bottom of the groundboard, do any of you know this dimention or a link to such info? I have all the other dimentions but not the important c of g.

Cheers

TL

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SniffTheGlove

SniffTheGlove

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OK, real simple.

1) Weigh the base (with out OTA)

2) Weigh OTA

These give you the combined weight for the platform

CofG for the OTA is easy, just measue the outside of the OTA and divide by 2 to get the radius.

Now for the base, put a broom handle on a table near the edge, then place the base on it's side on top of the broom handle to find the balance point. Measure the distance from the bottom of the base to the balance point. Remember to hold the base when finding the balance point so it don't fall and break.

Now add that measurement to the radius of the OTA and you have the rough CofG to work with.

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