Build Project: Dob Equatorial Platform

[SniffTheGlove]

sean here are the pulleys i will be using for my dob setup , my stepper is also 5mm shaft size , i will probably use the 4mm bore pulley and slightly polish the shaft with emmery and slightly ream the pulley to make it fit the shaft ,i hope this is of some help, Tony

motionco_Pulleys & Belts_Stock Aluminium 3mm HTD Timing Pulleys

Thanks, yes it will be helpful especially if I mess up again and also these people have motor/gearboxes as well.

Thanks Tony.

When you say using for your dob setup, do you mean EQ Platform or to actually drive the dob in Alt/Az

[ponytale]

Hi sean , it will probably be alt /az to start with then EQ/Platform.

[SniffTheGlove]

Hi sean , it will probably be alt /az to start with then EQ/Platform.

I will await and see how you do. I had hopped to do something similar later on as I was hoping to rebuild my Dob into a small and lighter "lowrider" design but after stuggling with this platform I am thinking about getting a EDxx on a EQ6 Synscan or syntrek mount to do most Astro Photography work.

At least I have just got a Canon EOS 350D off eBay for £101 that will help with some long exposure shots <1 min on the Dob as my old Dimage Z5 only does 4secs

[SniffTheGlove]

Update

I have taken some shot of what I have done.

First shot is of the platform with the north segment support wheels removed and a new wedge in place ready to be marked up.

Second shot is the new wedge that has be marked, cut and had the new bearing supports added. 2 bearings to support the radius of the north segment, 2 to support the rear of the north segment (just like Shane has done with his ball transfer units).

Third shot is the wedge back into it position(dry) and having the bearing supported drive rod epoxied into place.

Once fully cured tomorrow, I shall reattach the wedge to the bottom platform and then start work on the motor placement, yes that old stepper motor is having it's final try before being assigned to Focuser control (next project)

[SniffTheGlove]

With no load it requires 750grams of force to induce movement

With a 16Kg load directly on the edge of the northern end it requires 2Kg of force to induce movement

With a 34Kg load directly on the edge of the northern end it requires 4Kg of force to induce movement

The loads used was a 16Kg car battery and a 18Kg Concrete Block.

Update:

Now that I have replaced all things with metal bearings I did do a load test and now With the 34Kg load directly on the edge of the northern end it now requires 1.1Kg of force to induce movement which is much better.

Note to others.... Use metal bearings!!

OK, today I finally glued the main support as per the above photos to the bottom platform. Needs a quick coat of black.

The stepper was just not strong enough to move the load platform still, so I have now dumped that design and gone with what Shane used (Same PWM controller and and 4rpm motorgearbox)

These will take a while to arrive from China.

I have also ordered some shaft inline couplings from Technobot (6mm to 6mm) to connect the motor to my homemade M12 to 6mm shaft adaptor. I also got a 5mm to 5mm inline coupling as well for my next project (That the arduino and stepper motors will be used for - Motorised Focuser)

[Moonshane]

Nice one Sean

Those couplings are excellent mate. I'll be ordering a couple!

[SniffTheGlove]

My inline couplings have arrived.

Also, been thinking and struggling with the tangent arm drive. I am using an M12 coupling nut to tracking along the turning threaded rod but what I have noticed is that if you take the platform being horizontal the tangent arm is at it's shortest distance to the platform and as the platform rotates the tangent are mounting has to rise as well. This is fine as the coupling nut will rotate upwards moving the arm up but also the angle from the mounting point to the coupling arm increases extending the distance bewtween the two.

Now I don't know hao to over come this with out some overly complicated attachment method. Looked at a few designs and also Shane's photos but they two must get this problem.

How do I over come this ? Ideas

[Moonshane]

hi Sean

Do you have a pic?

it's important to get the arm (where it connects to the north sector at least) at the same angle as the north sector.

see mine. I have also added a skate bearing so it rotates. this way there's no upward movement.

that said, I have amended mine tonight (and it still needs a bit of tweaking) to be more like the one at the bottom of this thread

A new stepper motor driver circuit

I also have connected two threaded rod connectors with a piece of ali bar as this reduces any lateral movement.

[SniffTheGlove]

Thanks Shane, went to look at the url photo and used that idea.

My driving connecting M12 nut is encased in ply and epoxied in. I tried epoxying aluminium/steel to the connecting nut itself but the adhesion of metal to metal holds for a while but then breaks when under some strain, so encased in ply then I can epoxied better as it soaks into the wood better.

I have now put a t-nut into the ply sleeved driving nut and one into the vertical support of my north segment. I used a small strip (same as used for segment runner) and drilled 2 small holes and screwed into the t-nuts and then rotated the M12 driving rod, everything worked fine from platform horizontal to approx 5deg rotation of north segemnt when the ali strip started to twist due to the angles and the driving rod got harder to move due to the friction building up.

I replace the ali strip with a wooden tongue depressor (think wooden coffee stirrer but much wider) as this is semi flexible when being twisted. Drilled the holes and mounted this into position and tried the same rod rotation from horizontal. As it reached 5deg the depressor started to twist but the friction level did not change and I reached 7.5deg which is the end of the tracking run, I then rotated the rod in the other direction and everything went well, so repeated a few times and there appears to be not backlash or other errors. All seems well.

I have included some pics to show.

I think I will use 2 depressors mounted together, they still twist together OK but having 2 will double the strength to avoid slits appearing in the ends.

First pic is the platform fully loaded with 48Kg of weight directly over the north segment, my scope is 40Kg but will be further back, I am just adding extra load to see how the system works ith that sort of load.

Second pic is of the encased M12 connecting nut with a tongue depressor fixed into position

Third pic is the tongue depressor fixed with the platform in a horizontal position ready for tracking test

Fourth pic is the same as the third but with the platform at the 7.5deg rotation mark showing the tongue depressor slightly flexed (twisted)

[SniffTheGlove]

~Forgot the pics

[SniffTheGlove]

Finished off the black paint job today, now just await the motors and controller.

[SniffTheGlove]

The motor and controller arrived here today from China, I shall have a go at finishing the platform tomorrow now as I have just finished my motorised focuser project today and it's clear skies and getting dark now.

[SniffTheGlove]

At last finished the platform with the new motor and controller as used by Shane.

I have sat my scope on and it tracks once you have the correct speed pot setting.

The issue I am having now is wobble of the scope sitting on the platform when touching the OTA, will check things over later on when it's light and I can how to steady it maybe etc, otherwise I am happy I have finally finsihed it and now WORKS

[SniffTheGlove]

Woow hoo! Finished at last, that a long time that was with lots of humps and bumps along the way but now I have finally finished it, it's in the obsy with the scope on and see moves really smooth.

Here is a pic of the bottom platform with all the electronics.

The motor is a 12v 4rpm high torque motor which is controlled by a 12v 15A controller.

The main power comes from a 12v 7Ahr battery.

There are a few different circuits in use which I shall describe.

The battery feeds out to a BIG connecting block, off this connection block runs...

A 12v 40A automotive relay (which provides power to all the main circuits.

An On-Off button (located of side panel as shown is first pic), this controls the relay coil.

A direct 12v connection located on the side panel, this is for plugging in the solar panel recharger.

Once the relay is powered up (when On-Off switch is on) I then run 2 more power outlets on the side panel, one is for the rear OTA fan, the other is for my home built motorised focuser. Now there is one outlet left plus a 2 way switch. The outlet runs to a hand controller allowing me to power up the tracking motor, the 2 ways switch is a DPDT switch wired up to provide reverse polarity to the motor, the cable run from the switch to the motor and then to the end of run limit switches that have diodes (IN4001) to allow for both limit switches to to work depending of polarity.

The 2nd pic of of the scope on the platform as it is tracking, I could not get the entire scope in the pic as I had no more room to move back when taking the photo.

Main testing is hopefully tonight is the skies stay clear.

[Moonshane]

this looks brilliant Sean. Glad we got there in the end. being in an obs you'll only need to tweak it for alignment once I suppose you lucky thing!

your wiring is very neat indeed and some innovative electrics. mine is much simpler (like me )

[SniffTheGlove]

this looks brilliant Sean. Glad we got there in the end. being in an obs you'll only need to tweak it for alignment once I suppose you lucky thing!

your wiring is very neat indeed and some innovative electrics. mine is much simpler (like me )

Simpler! I copied you in the end for equipment, then the side panel from your photo's gave me the idea. Credit goes mostly to you Shane. Thanks.

I have done a few smaller odd jobs now everything was done. I have marked out on the floor in thick permanent black marker the Celestial North - South which currently for me is 2.3deg off true north according to some USA website bearing generator. The platform now sit directly over this line and in orientation (we will see how good once I go through the platform alignment test).

I then marked out a straight line on the focuser and draw tube(EP Screw) in medium permanent marker so I will always know when everything is aligned, then I collimated the scope.

I am now working on a sliding weight that will be fitted to the rear of the OTA as the extra weight of the stepper motor etc has put it off balance, also with the addition of using 700grams of Canon EOS 350 on the focuser then I need to be able to counter-act the weight easily with out fiddling with adding weights to the rear of the OTA, I shall just loosen the lock screw and slide the weight backwards down the OTA until it balances (just like the old fashion weight scales)

[Moonshane]

aw shucks. cheers Sean.

hope it works well.

I used a small dovetail bolted to one of the tube rings and a small weight http://stargazerslounge.com/diy-astronomer/109577-latest-dob-mods-fan-balancing-weight.html might give you some ideas.

[SniffTheGlove]

Today, I did a few mods to the platform.

1) Re-did some of the wiring as I was finding it difficult with my spinal problems to get down onto the floor to adjust the pot to adjust the motor speed, so I got some multi-core cable inside some plastic sleeving and moved the pot onto the handheld controller that contained the tracking on/off switch, so now there is the pot with it's knob and now I can adjust the speed whilst sitting/standing/using the laptop etc which is much much easier. I need to do a little more work to put one more cable core into the sleeving to the handheld controller so I can move the forward/reverse switch up there as well as this is currently on the bottom part of the platform.

Mods still to do on the list are...

Replace the tangent arm from using wooden tongue depressor and replace with a unbreakable but flexible ruller as this will make it take the angle changes easier as the woden tongue depressor is fine but creaks a bit.

Put a 6mm bolt in the middle of the top platform with at least 7 teflon blocks (or ball transfer bearings) around the OD, this is so I can replace the current swivel base which only has 3 blocks and can induce a slight rocking of the rocker box wheh tilted of horizontal. This will also reduce the total height of the scope by 3 inches.

An update, the platform works great and already had a good webcam session on the moon.

[spaceboy]

Great job there Sean!

[SniffTheGlove]

Put a 6mm bolt in the middle of the top platform with at least 7 teflon blocks (or ball transfer bearings) around the OD, this is so I can replace the current swivel base which only has 3 blocks and can induce a slight rocking of the rocker box wheh tilted of horizontal. This will also reduce the total height of the scope by 3 inches.

.

First off Thanks Spaceboy!!!

I have done the above mod a few days ago, I used 12mm thd rod in the end as it being a larger dia makes for a bit more stability over 6mm. I also put 8 teflon strips radiating out from the 12mm thd rod centre. This has lowered my O/A height by 3inches and also made the OTA a bit more stable.

[sandspider]

Hello guys,

Fantastic work, I initally thought I could knock one of these up in a couple of weekends, but I think I'll have to do a bit more planning.

Did you manage to get any nice images from the scopes once they were mounted?

[SniffTheGlove]

Hello guys,

Fantastic work, I initally thought I could knock one of these up in a couple of weekends, but I think I'll have to do a bit more planning.

Did you manage to get any nice images from the scopes once they were mounted?

Hi Sandspider,

The main problem I have had is that since complting the platform I have only had a few clear nights, but one these days I got good visual tracking and also good tracking for webcam imaging. Because I am still new at all this imaing it is taking me time to get use to all the equipment and trying out different senearios takes time.

My first and only decent imaging is of Mare Crisium and can be seen here http://stargazerslounge.com/imaging-lunar/138372-stg-first-lunar-image.html

I have also tried my EOS350D but this is taking a bit longer to get used to due to the fact I have had no clear nights for weeks now.

Do have a go at building a Platform Sandspider, my advice is yes it's simple but does a take a while and then afterwards you make your mods.

Consider the following...

Weigh your scope to get the weight and cofg

Decide on how you are going to fix the south end.

Take time to cut the north segment, measure measure measure then cut.

Use bearings instead of wheels to rotate and support the platform.

Make sure the motor you use has enough torque to do the job.

Put all the controls (on-off switches, pot etc) into a hand controller (saves bending down all the time to adjust)

For me I got great satisfaction taking my first tracking image knowing that my build and advice from Shane and others has made my hobby more stimulating.

[sandspider]

Sean,Wow, your tracked picture is fantastic!

I really do think I will have a go at this. I just have to finish of a hen house first!

My brother in-law has a wood working shop, so I might ask a few favours

Would it be OK to check back with you if I come across problems?

Mark

[SniffTheGlove]

Sean,Wow, your tracked picture is fantastic!

I really do think I will have a go at this. I just have to finish of a hen house first!

My brother in-law has a wood working shop, so I might ask a few favours

Would it be OK to check back with you if I come across problems?

Mark

No problems at all Mark.

How many hens do you have? I have had some a few years back and the last one died a few months back and I am thinking about getting some more rescue hens again.

[sandspider]

We have about a dozen hens, one cockerel and a duck. Numbers go up and down as the years go by, and the fox gets hungry

Rescue hens are a great idea because they are bred for laying. A friend of mind got about 20 and the all scrubbed up nicely after a few weeks TLC.

If you get them give them a dose of Verm-X, its a natural wormer but it's also a bit of a tonic and helps them along.