Crayford Rectifier!

[ollypenrice]

That I loathe Crayfords for imaging is something I may have mentioned before. 

I've just acquired a Moonlite as part of a deal on a second hand Meade ACF and I don't trust it one bit. It looks very pretty but the surface on which the roller rolls looks like smooth anodized aluminium, though I haven't taken it to bits to find out. This distrust put me into Heath Robinson mode and I have invented Penrice's Progressive Altitude Sensitive Crayford Deloader.

- Parallel with the focus drawtube and to one side of it we install a circular alloy tube of about 3cm diameter. It is attached to the scope side of the focuser.

- Inside this tube, running on ballbearings, runs a counterwieght of about 3/4 the weight of the camera and filterwheel.

- From this counterweight and running towards the front of the OTA extends a length of nylon twine.

- Fixed near the back of the OTA is a pully, round which the twine passes before heading back to the camera, to which it is attached.

So now, with the tube on the zenith, the CW is pulled down under the full force of gravity to remove 3/4 of the lifting requirement of the Crayford. (The balance factor could be set at 100% but it's nice to keep a little tension in these systems.) As the angle of the OTA is lowered towards the horizon both the lifting load on the Crayford and the effect of the conterweight diminish in unison.

You know, I might actually make one. This instrument is going to be used robotically so won't have anyone babysitting it and losing subs to slippage would be most distressing.

I'm sure there will be lots of similar devices in circulation already. Or am I really just a complete nutter?

Olly

[Psychobilly]

I have seen other solutions but not that one... and your idea shouldn't require "manual intervention" and allow for remote focus adjustment...

Most of the others I have seen are mechanical locks/supports... IIRC  Baz did something with a plate and threaded rods...

Peter...

 

[michael.h.f.wilkinson]

2 minutes ago, ollypenrice said:

That I loathe Crayfords for imaging is something I may have mentioned before. 

.....

No? REALLY?? 

 

3 minutes ago, ollypenrice said:

.....

I'm sure there will be lots of similar devices in circulation already. Or am I really just a complete nutter?

Olly

That is not is not an either/or question, is it?

Still, an ingenious solution. Several things stimulate men to genius:

1) the love of a woman, although that more often makes men behave like complete fools

2) laziness: the amount of effort put into devising methods to avoid work often outstrips the actual work by a large margin

3) being scolded by a woman: might be the same as the one in (1), and have been caused by (2)

4) rage: pure, blind anger can lead to astounding insights

 

Cheers

Michael

 

 

[ollypenrice]

Certainly '4' in my case!!!!

Olly

[andrew s]

Not sure about the mount you are going to use Olly but, a meridian flip might be a challenge for your design. Many years ago I was in Cambridge at the Observatory there and they had a tiny version of what will be the Large Synoptic Telescope (or something similar) and it had weighted leavers doing a similar job on the main mirror. The advantage of leaver is it can stand a flip.

 

Regards Andrew

[ollypenrice]

1 minute ago, andrew s said:

Not sure about the mount you are going to use Olly but, a meridian flip might be a challenge for your design. Many years ago I was in Cambridge at the Observatory there and they had a tiny version of what will be the Large Synoptic Telescope (or something similar) and it had weighted leavers doing a similar job on the main mirror. The advantage of leaver is it can stand a flip.

 

Regards Andrew

I can't see why my system would have a preferred 'way up,' but I might be missing something. (Note Michael's refusal to eliminate the possibility of my being a nutter!)

Olly

[andrew s]

1 minute ago, ollypenrice said:

I can't see why my system would have a preferred 'way up,' but I might be missing something. (Note Michael's refusal to eliminate the possibility of my being a nutter!)

Olly

You can't be more than a nutter than I. I probably misunderstood the design but I was thinking any pulley would invert during a flip if attached to the scope and the tread would fall off.

Probably a fantasy on my part.  Reagrds Andrew 

[ollypenrice]

Just now, andrew s said:

You can't be more than a nutter than I. I probably misunderstood the design but I was thinking any pulley would invert during a flip if attached to the scope and the tread would fall off.

Probably a fantasy on my part.  Reagrds Andrew 

Hmmm, you may have a point. I can't visualize the trajectory of a mount doing a flip so I'll go and do one and watch it! The thread could pass through a curved tube instead of a pulley, though.

Olly

[Psychobilly]

Or the weight go sliding down the tube  towards the scope so a "buffer spring" at the end maybe...

Now if it was on a fork mount on a wedge then there would be no need for a meridian flip ...

Peter...

[steppenwolf]

Quote

Or am I really just a complete nutter?

Complete nutter.

Quote

Now if it was on a fork mount on a wedge then there would be no need for a meridian flip ...

I've recently been told off by a reader for suggesting that another reader should de-fork their SCT for imaging and buy an equatorial mount that could also be used with more suitable AP instruments rather than use a wedge. I stand by my original suggestion ........

[ollypenrice]

53 minutes ago, PBS said:

Or the weight go sliding down the tube  towards the scope so a "buffer spring" at the end maybe...

Now if it was on a fork mount on a wedge then there would be no need for a meridian flip ...

Peter...

Now if it was on a fork mount on a wedge then there would be no need for a meridian flip ... ... because you'd have given up all hope of getting an image long before the obect had reached the Meridian and be well into you're seventh pint of anaesthetic down at the Greene Man!!!

lly

[Psychobilly]

Oh come on gents that's a defeatist (but realistic) argument... I know it saved me a lot as my darkest and lowest horizon  was a gap through the trees either side of the meridian.. then again I like(d) a challenge

You could limit the weight travel toward the scope using something as simple  series or regular drilled holes and a pin this would still allow you to have decent focuser travel to cope with diferent setups..

A weight on a linear bearing track is another option...  or 40mm round steel bar is approximately 1kg/100mm and you can get 40mm ID linear bearings

It's a quiet day in the orifice...

Peter...