Altitude Slow Motion Control

[rmcpb]

Found this link on CN and thought it was worth showing here as well. Simple and brilliant :)

http://www.atmob.org/Articles/JoeR/DobSlowMoControl.html

[ving]

very good find rob...

this is on my things to do list now :)

(along with 10 thousand other things

[rmcpb]

Yeh Dave, it would be very easy with the GS dobs as they already have the bolt in the centre of the bearing for the spring tensioner.

[ving]

just have to figure out where to get the knob from... wouldnt get one from bunnings would you? dont think theyd have me :confuse3:

[rmcpb]

Probably not real necessary. You can get really close manually already or you wouldn't be able to see anything so just get it close manually tighten the centre bolt and gently adjust with the turnbuckle, shouldn't take more than a turn or two at the most. The knob does look good though :)

I think the main use would be when changing eyepeices or observing near the horizon or zenith.

[ving]

so... do youthink its worth doing? my current eps dont overbalance the scope (except for the 30mm SV) as long as i have one spring on.

[RAJAH235]

Why not use a simple 'brake band? :D L.

[vindictive666]

ive got the problem of my BFG over balancing (quite a lot actually)
when ive got the solar filter on it plus the 2 inch barlow with the 2 inch 32mm GSO, it has a definite tendency to drop to the ground.


i managed to find some speaker magnets havent had a chance to use them yet
though.

so i reckon it seems to be an other good alternative.

might have to invest in a turn buckle and a drawer knobbie :) i wonder how he attached it (drilling a dirty big hole thru it ?)

:evil: :evil2: :thumbsup:

[slice of heaven]

Similar principal to what I fitted. Though I used a triangular shaped plate backed with rubber which sits on top of the brace I fitted to strengthen the base. The original bolt I fitted with a compression spring a washer and a 25mm circular super slider.The rubber side of the plate sits against the alt bearing. The slider sits against the plate and stops the bolt from turning as you change alt.A simple arrangement which only means fitting the tensioning bolt (if needed) during setup.
Not much tension is needed to change the feel.
I only use it when theres heavy dew or when the kids are using it. Sticking a 600ml coke in the focuser and movement is still very very acceptable.

[RAJAH235]

When you unscrew the hook/s, the centre piece is just a flat/rectangular section. Simply drill 2 suitably sized holes thru the knob & chisel out the bit in between, or drill one BIG hole & silastic it. :D L.

[rmcpb]

Along the same lines I found this site on leveling a scope:

http://web.infoave.net/~billgriz/xti-base.html

[rmcpb]

Antoher one on dob mods:

http://www.geocities.com/smalldob/equipment_modifications.htm

[ving]

bored rob?

[vindictive666]

gday all

i had a go at the mod
however when i turn the turnbuckle the short arm just turns on the centre altitude bearing bolt and it doesnt matter how thight you turn the bolt in
so it looks like you are gonna need that clutch knob :( or if anyone has an other idea ? on how to solve that little prob ? :)

:bashcomp: :fight: :thumbsup:

[slice of heaven]

Vin if your scope is nosediving I'd recommend using weights to balance the scope rather than using a friction clutch setup to cover up the problem. For the eps and barlows I use my scope balances perfectly. My alt motion I stiffened a slight touch with felt strips and have never found a need to use the springs. But I've fitted a Telrad and removed the finderscope which lightened the front nicely. The clutch setup I made is for extreme conditions...kids..heavy dew.
Starkler has weights fitted for using his hand grenade and has mentioned he's removed his springs so he must have worked through this and for him they aren't necessary any more. He might be able to shed more light on the balancing issues with the use of heavy gear up front.

[acropolite]

Hey guys, the disk type clutch is a good idea, but the locker and adjuster sucks. Why not modify a pushbike type locking cam to do the same thing, i.e. the cam goes in the centre of the disk and tightens. I'm sure you could buy one for a couple of dollars. Here's a pic of one.

[slice of heaven]

That would be handy to lock the scope while changing heavy eps Phil.( I'm not lucky enough to be in that class).

[rmcpb]

I don't think the original idea was to cover the effect of an unbalanced scope, the speaker magnet trick is the best here. The shackle adjuster is great to allow changes in eyepieces followed by re-balancing with the magnets, or to allow fine tracking adjustments.

As for the problem Vindictive has, the material used in the bearings on GS dobs is very smooth. When I make mine I will have a layer of wood between the bearing and the metal to increase the friction levels. Hopefully, this will make the problem go away.

[fringe_dweller]

The guy who made our scopes and taught us stuff in the beginning long ago uses aquarium cleaning paired magnets - so we do to - they arent exactly cheap - but more conveniently weighted/shaped and smaller for finer increments than the free old speaker magnets i reckon - i also wrap them with one layer of duct tape to stop them scratching tube.
Kearn

[Starkler]

I use lead divers weights of the flat rectangular type held on by a tie down strap.
1kg for $5 , 500g $2.50 and they are only about 1cm thick

[vindictive666]

gday all

i had an other crack at the problem yesterday without much success iam afraid

the plate that sits against the altitude bearing still moves against the surface of the bearing (the plate is made of wood) so unless iam prepared to remove the 2 bolts holding the bearing (no keen to do ) and shoving those thru the plate as well because that would mean (in my case 12 inch dobbie) removing the mirror assembly ect ect. (colimation again)

or screwing 3 or 4 self tappers thru the plate into the bearing surface however iam not sure if the bearing house is solid or hollow if you know what i mean so untill i can think of a another way this project is come to a halt :) and yes it was a project i wanted to try because i had all the gear needed. :)

however ive got some speaker magnets anyway so its not a real problem :)

what i liked about it was the fine adjustments you could make with the turn buckle which would have come in handy in my case :)

ps

i made 2 plates in which the short handle sat plus the handle(made of alluminum) itself moved as well but i fixed that by glueing 2 bits of (small) alluminum on iether side of the handle on opposite sides of the plates.

the plates are almost but not the same size as the hub.

i would post pics but thats hard to do with no camera :)

:thumbsup:

[ving]

hmm... sounding rather complicated now vin...

[vindictive666]

yes ving

i wonder how that clutch knob works then maybe a 10 inch dob a lighter
it seems to work a litle on going down but slips moving it back up i figure to much weight that why you gotta anchor the plate
is a really shame. :)

[ving]

what if you were to use a rubber washer as a "clutch" vin? itd prolly stop slippage :)

[vindictive666]

actually i might try that ving all i have todo is find some :)

[ving]

god I am brilliant!!! :D
all bow down to me!:prey2:

PRAY TO THE MIGHTY COW GOD!!!

:p

[vindictive666]

i think ill pass on that i dont cowtow :)


:rofl: :scared3: :thumbsup:

[ving]

just call me "Cow Tse Tung!" :P

[vindictive666]

:rockband: :bowdown: :bowdown: :bowdown: :ship1:


hiya ving iam back to let you know that rubber idea works so it a sucess! :)

i made it the same diameter as the plates i had a old mouse pad loafing around and made a plate out of that it works



:party: :sunny: :bowdown: :bowdown: :bowdown:

[ving]

sweet, on ya vin :)
congrats!

[slice of heaven]

Extremely.

Now who would've thought of using rubber?

[ballaratdragons]

My speaker magnets work a treat. Because I rubber backed them I slide them up and down the OTA for perfect balance. I also use both springs attached so when I change EP's the scope doesn't move.

Easy and cheap.

[mick pinner]

firstly let me say that l have only looked at dob mounts in passing and not closely but reading these comments on balancing etc, l must ask why can't you mount a worm drive electric motor on one side, this would give you control over the balance issue and also prevent the scope from moving up or down if it was bumped. one other thing l have wondered and l realise the idea of a dob to keep the price down but why are the ota's not held in a cradle so they can be slid one way or the other to off-set the addition of ep's etc.

[slice of heaven]

A cradle can be fitted Mick.
My 12" Parks has a plywood box clamp arrangement. To adjust the balance,it is as easy as releasing 2 clasps and sliding the OT to the required position.

The gs dobs are built around the optics.
The price dictates how the scopes are supplied.
A few cents for 2 plastic side bearings V A few $$$$ for an adjustable setup and sturdy usable base.