Hi, would you'll have any pics of the clutch and/or braking systems on different mounts, opinions on wet and dry clutches, materials that can be used, teflon and ebony star formica and different methods of engaging and disengaging motors to the drive train.
hi, any help with info on clutch designs would be really helpful.
My application is a simple, a timing pulley on a 20mm dia steel shaft.
How do I design a clutch to engage/disengage the pulley and thereby the motor drive?
is it usually done with two concentric shafts, with the worm gear on one, and the main ra or dec shaft on the other, with a slip clutch inbetween? if so, how is the clutch face moved toward the drive gear without disrupting the drive train?
i was thinking of using 24v electromagnetic clutches from printers, but i presume these couple the input to the output when the voltage is applied, else it will allow the driven shaft to rotate free. is there a clutch which does the reverse, so with no power, the input is coupled to the output, but when power is applied, the output is decoupled.
that way, i can conserve power by applying a voltage only when i need to move the scope assembly by hand, at othertimes it remains coupled to the drive train.
hi bojan,
i;ve seen this concept in a few pics, but how are these plates arranged on the shaft?
does one rotate freely on the shaft while the other is fixed to the shaft? if so, one plate would need to move axially to contact the other plate, then how is the drive train or worm kept engaged. is a cantilever used for the axial movement
One is attached on the shaft, another one is driven by the motor via reduction.
There should be enough friction between them for mount functionality, yet it should be possible to move the telescope relatively freely against friction (which can be adjustable)
In EQ6, it is a bit different.. picc 5-7. pic 8 shows the clutch.
the clutch plates are always engaged and the motor torque after reduction has to exceed slip torque of the clutches?
how is the plate usually fixed to the shaft? i found a few shaft collars that have bolts in them which i'm guessing can be bolted onto plates? any other methods?
the clutch plates are always engaged and the motor torque after reduction has to exceed slip torque of the clutches?
Yes, this is how I did it on my eq mount (doesn't exist any more).
I did the same thing on my dobson.
And this is the case on other designs as well.
Quote:
Originally Posted by alistairsam
how is the plate usually fixed to the shaft? i found a few shaft collars that have bolts in them which i'm guessing can be bolted onto plates? any other methods?
Well, that depends on the design.
In EQ6, you have shaft with its own bearings, then worm gear on the shaft with its bearing, and then the screw with brass button that slides with certain amount of friction in the groove of the worm gear, so the friction is adjustable.
Byers worm gears have friction clutch, very similar in design to car clutch - the friction is adjustable by 6 screws close to the perimeter, positioned at 60°. The bearings are machined sleeves (not ball bearings) if I remember correctly.
two quick photos of my RA axis and clutch showing what slips and what
is locked.
The cork wafer on each clutch face is from old drink coasters with
masonite tops and cork backing.
This idea was suggested by Dave G...it works beautifully.
The scope is free to move around then a quick slight tighten on only
2 of 4 pressure screws makes the scope engage with the worm gear.
Thanks steve,
from what i understand, the plate closer to the bearing is fixed to the ra shaft and does not move. so by tightening the bolts on the other side, you're pressing the cork onto the worm wheel?
do you have anything preventing the bolt going through the cork
I was thinking of using the ikea cork coasters but will have a few beers and use them instead!
did you machine the shaft collars and the plate?
i presume you only need to get the bolts tensioned right, and then you don't need to adjust them at all?
when you loosen the bolts, does the worm wheel move axially at all, as then it would misalign with the worm?
is the worm wheel on a bearing on the shaft?
from what i understand, the plate closer to the bearing is fixed to the ra shaft and does not move. YES, so is the other plate, snugly pushed up to the face of the worm and then LOCKED forever to the RA shaft too.
so by tightening the bolts on the other side, you're pressing the cork onto the worm wheel? Not quite, pressing on a floating plate of PVC which then presses on the cork.
do you have anything preventing the bolt going through the cork As above
did you machine the shaft collars and the plate? yes
i presume you only need to get the bolts tensioned right, and then you don't need to adjust them at all? Just pushing the collar up snugly then locking it is enough for me to be
able to move the scope (well balanced) around and it stays where I leave it...acts like a good friction brake.
when you loosen the bolts, does the worm wheel move axially at all, as then it would misalign with the worm? No play what so ever...snug as
is the worm wheel on a bearing on the shaft? No, just a very close tolerance fit.
thanks, its a lot clearer now. i noticed you used a similar design on your homemade focusser. very nice work.
last few questions on teflon and ebony formica.
i've seen a few scopes using teflon as clutch plates, is'nt teflon supposed to be the most slippery substance, how is it then used in clutches which needs a bit of friction?
would you have any idea on ebony star formica? read on the siderealtech site that it was used as a clutch.
is teflon available at bunnings or stores as sheets or blocks?
i've finally decided on using a split collar clutch around my steel shaft with a lever to compress and release it, thereby gripping or releasing the shaft. this collar will be fixed to my fork frame. in principle, it will do the same job as yours, providing slippage when needed, just a different type.
last few questions on teflon and ebony formica.
i've seen a few scopes using teflon as clutch plates, is'nt teflon supposed to be the most slippery substance, how is it then used in clutches which needs a bit of friction?
would you have any idea on ebony star formica? read on the siderealtech site that it was used as a clutch.
will post pics when done.
I have no idea how suitable these would be Alistair.
Someone, hopefully, will chime in who has experience with this.
I am curious however to find out how paper goes as Bojan has suggested.
Next strip down I might try this. Paper possibly could provide the same
slip/grip characteristics as the cork but enable the worm gear to
move even less sideways microscopically, as it surely does in my setup.
Lokking forward to see what you come up with Alistair
I went back to your design and Bojan's suggestions, and since I don't have access to any metal working tools or even metal, I made it from what I love to work with, wood.
So it might look amusing, but it does work as you mentioned. provides enough friction for the motor to turn the RA axis, but I can manually turn the RA axis without stressing the motor gear train.
I'll be using a thinner ply piece as the friction plate. but as it is, there is no deflection and provides ample hold, and once adjusted, I don't need to adjust the pressure.
This is a homemade fork mount that I built for an 8" F6 Bintel reflector that came with a Dob mount. so still work in progress, but I have done some preliminary tracking tests and it tracks well for around 10 minutes. still needs refinement, but getting there.
