Dob Wedge and Cart

[mick pinner]

l had a couple of hours today to have a look at the dob wedges and have come up with a first idea, this wedge will be made as an add-on for the dob carts and will just bolt into place, it will be adjustable to any latitude from about 20-50 degrees and will then lock into place as well as be able to moved on the cart forward or backward to address any balance issues. These pictures are just to give an idea of scale with the cardboard disc being the size of a 12" base, l will brobably have it mounted to the cart tomorrow and will post some more pics.

[netwolf]

Simple an to the point.. A good start, i can see myself geting one of these.

[davidpretorius]

looking good mate!!!

i want some pics for the website!!!

[acropolite]

Now dave, you could motorise that and given a constant thread pitch maybe computer controlled as well......

[davidpretorius]

that is exactly what i want to do. I believe that you can have up to 5 or 6 models of mick's dob buggy, with wedge, eq platform, alt/az drive etc

i am very excited about this one!!

[acropolite]

You're easily excited dave, better lay off the red cordial.....:lol2:

[Starkler]

What you end up with here is a variation on a fork mount.
I have thought about this idea myself and there is a few practical issues to consider.


For a person in Melbourne the base will need to be tilted 90-38= 52 degrees for the azimuth motion to become RA.
considerable modifications to altitude bearings will be required to make them captive
strengthening of the base will be required
the scope will need to be correctly balanced so that the dob wont take off 'downhill' when pointing off to the side
the focuser will end up at odd angles at different parts of the sky

[elusiver]

top points starkler! especially the one about the focuser.. i didn't think of that one.. :D

and mick.. does mrs pinner know you're welding on the kitchen floor and putting dob wedges on the kitchen bench?? :P ;) :D

el :)

[netwolf]

however I would think that the wedge would only be used for non-visual ccd work, hence does the position of the focuser matter. The dob can still be used in alt/az mode with tracking motors and you can throw in a field derotator for longer viewing. I think Mel bartels stepper system would be the best bet to use. As it can switch between alt/az and ra/dec. It also has a field derotator component.

[mick pinner]

l read and understand your concerns Geoff but what is the alternative?, my ultimate aim is to have a more rigid and user friendly dob design which l am working on at the moment such as captured bearings and tube rings to allow the scope to be balanced by shifting the centre of gravity, as for the focuser position dob owners will not suffer any more than SCT or Newt owners in this regard, if people persist in buying dob scopes as a cheaper way into astronomy then deceide to tackle photography they will need some method to achieve this and my aim is to give them an affordable way of achieving this.

[gbeal]

Great idea, and one I have pondered (no relation Paul) myself.
The focuser position is a pain in any newt, and I have made a split cradle that surrounds the tube proper, and has the altitude bearings mounted on the outside. A suitable clasp pulls this cradle together, but when released, slightly, allows the tube to be rotated. I can then roll the tube to afford the desired eyepiece position.
Keep at it Mick.
Gary

[Orion]

I think that you are doing a good job Mick.
There are always good and pad points to different types of telescopes and mounts and the same goes for the dob wedge but I believe that people will get more satisfaction out of their telescope with the wedge.
The prototype will tell how useful it will be and how well it will work.

[mick pinner]

the cart itself is almost finished so l thought l would post a couple of pics with the wedge attached,it can be used as a flat dob cart with levelling adjusters and it can have the wedge added at a later stage, it can also be raised from a ground clearance of 50mm for flat ground to 120mm for more uneven surfaces the wedge is fully adjustable from 20 - 60 degrees. as with the tripod wedge the wheels are 8" pneumatic with bearing hubs and the front wheel is a greasable roller bearing. it breaks down into 8 seperate parts including the steering handle and weighs around 10kg with the largest section being only 680mm long, the wedge as a seperate section is 600mm wide and 780mm long.

[davidpretorius]

even though you and i have been communicating a lot on this one, i must say i am very impressed.

well done mate, lucky i am taking the wagon to star camp, i will have to drop by and take at least a dozen!!

[netwolf]

Looks good Mike, when can i get one..
How do you park it, i mean does it have a break or just stick something under the wheals.

[asimov]

I made such a cradle for mine as well. I also added rubber wheels to the cradle for easy tube rotation.

[h0ughy]

you have done a great job there Mick! Maybe hit a winner, enter it for next years New Inventers!

[mick pinner]

one day closer to completion,
pic 1. the scope can be used for visual observing when the wedge is in it's fixed flat position.
pic 2. simply raise the wedge to the desired latitude for polar alignment.
pics 3 & 4. the rear sliders can be left at the fartherest point backward or slid forward to increase the angle of the wedge and also if necessary move the centre of gravity of the scope further towards the centre.
the final fine adjustments are then made using the threaded rod and locking nut.

[davidpretorius]

and then we motorize it!!


well done mick!

[mick pinner]

there are a few final touches to finish but this is basically the finished item, a top plate for the wedge will be fitted but l haven't deceided what material to use yet.

[h0ughy]

Now remember Mick to make is completely Authentic put together flat pack kit it has to be in chinese, with bolts missing and new components added but not in the diagram!!!

You have done a fantastic job with that buggy!

An addition to add might be one of those inclinometers to attain the correct latitude angle?

[davidpretorius]

i like that

assuming the pivot point on my dob is close to the centre of gravity, this point is 560mm above the base.

if i put it on a 50degree angle, this centre of gravity moves aprox :

sin (50 degrees) = distance moved divide 560mm

therefore distance for centre of gravity moving = 428mm

you had better check my maths

[cahullian]

Nice one Mick I bet the Dob owners are hanging for the finished product. I know I am.

[Orion]

Nice work Mick. Does one of the three wheels have a locking device on it to stop it from moving if it's accidentally bumped?

[mick pinner]

when the cart is set up for viewing it has 3 wind down adjusters to stabilize and level itself.

[asimov]

Nice job Mick, Looks really good. Well done.

[mick pinner]

thank you Asimov, greatly appreciated.

[Orion]

PM'ed you Mick.

[netwolf]

Great Work Mike.. looks very sturdy.. a bit like the Trycycle i had when i was a toadler.

Will there be a handle to pull it along at star party's.. I can imagine going in circles around all the small refractors goin ha ha mine is bigger. :cool:

[mick pinner]

yes there is a handle, forgot to put it in the pic, it screws into a thread on the front wheel.

[iceman]

It looks really great Mick, but at that angle, what stops the scope from falling off?

[netwolf]

Iceman, counterweights.. Like a big battery seated on the back axle.
Mike maybe you can have a small area to locate a battery or counterweight.

[davidpretorius]

we have discussed this afternoon on the phone, a 20mm rod say 150mm long that is bearing driven and ready for motorizing will be investigated tonight as part of the wedge option.

there will be a 300m plate with a bearing for rotating when in the flat and also when at the angle another bearing to allow to rotate freely

hopefully mick will have some pics soon of this.

also my height above the base for centre of gravity is 560mm, so even at 50 degrees, that does not go outside the area of the wheels.

[davidpretorius]

should be no need for counterweights!

[mick pinner]

Mike, there are a number of ways to secure the scope by either having brackets to hold the bottom plate of the dob or if motorized a central pivot rod. The balance of the scope is not an issue as the centre of gravity even above 50 degrees sits well inside the triangle created by the wheels, this coupled with the length and weight of the front wheel carrier will ensure the scope does not tip.

[netwolf]

Hi Mick,

Can you provide any idea's on cost for building one of these? Material Cost, labour cost etc.

[netwolf]

Mick,

Are there any updates on this project??

Regards

[ballaratdragons]

Mick, I hope you can bring your Dob buggy/wedge to the Snake Valley Star Camp. You are welcome to sell them at the Camp! :thumbsup:

[mick pinner]

davidpretorius will be bringing one of each for people to have a look at, l will probably only make it for one day and night unfortunately, l'm flat out making sure l have them finished in time, there is still a bit of testing to be done yet to make sure all areas have been covered, l'm also having to follow some other projects such as mounting plates and weight systems as well as finishing of some jobs from work that l was commited to before l deceided to take on the telescope accessories buisness, by the way l thought about your buisness name idea but came up with astroshield telescope accessories, web site has started www.astroshield.com.au

[netwolf]

Excellent news Mick, finaly some more Aussie made astronomy gear..

[ballaratdragons]

You are a busy busy boy! Good luck with it all Mick. I hope you get some orders at the Camp. Will be good to meet up.

[mick pinner]

it's a lot tougher than l thought, so many people to deal with and so many things to keep track off, but l think a change of direction after 32 years of painting cars will be reason enough for an old bloke to keep at it.

[mick pinner]

some pics of the cart for large tripods that l have finally finished.

[davidpretorius]

one word:


beautiful!!!!

[netwolf]

Mick,
excellent work..
Just wondering how difficult would it be to have the option to add to this that would make it like an equatorial platform. I know you have a wedge design add on to this. Has this been something you have considered. As this would keep the dob flat on the cart and still allow equatorial tracking like Mike's round table platform does.

Regards

[mick pinner]

if you look at the dob cart with the wedge the wedge will fold flat

[astroron]

Mick, I have a 16" truss dob what is in the future for dobs over 12" on your carts with wedges?astroron :)

[ving]

thats a work of art mick :)

[davidpretorius]

I am taking my 10" dob to Micks place on the friday of the star camp at the end of the month. All buggys (dob, dob with wedge, tripod) are making the trip to ballarat for serious measuring against every scope that is there.

Any detail you have re photos, measurements of the base, weight, rough distance of the centre of gravity from the base will be most welcome.

Nothing is ruled out at this stage. Mick wants everybody's wish list from the star camp, and if you can't be there, please forward those wishes with pictures / sketches.

[ving]

found someone elses take on a dob wedge... simple it is...
http://www.haven.k12.pa.us/orfft/wedge.html

[davidpretorius]

me not like the battery counter weight!

fallie over much!

micky pinner wedge buggy good!

[mick pinner]

the revised dob cart with provision for lap top computer stand, it will sit on a tray being made to go on top of the front post, Dave P's idea.

[davidpretorius]

honey, I want a divorce!!

i have found another love!!!

SOLD!

Is it friday yet????

[ballaratdragons]

Great item and well made. Will be good to see it in the flesh on Friday! (well, in the steel)

[ving]

and its in dragons colours ken :D

[ballaratdragons]

I will have to get one then David, even if I don't use it. :lol:

Red & White!!!!! Coooollll! A Dragon Buggy! For Dragon the Scope around :P

[ving]

no pun intended obviously :P