16in Lightbridge exterior plywood dob base build

[Mike73]

Thanks for the pics Astromonkey, I'm also going for the elliptical heater pad from Kendrick. Can you remember what silicone you used to fix the heater pad to to secondary and mirror stalk?

[astronymonkey]

Hi Mike,

It depends on the design of secondary holder you have.

I have a plastic unit (see top pic above where the mirror is removed showing the heater in the bottom of the plastic housing) where  the mirror is held in by a single front clip-  so the heater pad was basically held into the holder using electricians tape and then the mirror was put in directly over the top and holds it down.

There is another Lightbridge secondary mirror design though where the mirror is attached directly to the salk  and in this case I think you would need the split elipse design from kendrick which allows the heater pad to be slipped around the post and attached with silicone.... in this case I would just use some clear silicone sanitary sealant over the topn but you need to make sure the pad it firmly against the mirror rather than being insulated by  layer of silicone.

What version of holder do you have ?

cheers

[Mike73]

Mine is attached via a stalk with no room around the outside for the split heaters but judging by the text on the Kendrick site I guessed the elliptical heater is the right one? I'II send Jim these pics and see what he says.

The current dew heater is good but on heavy nights of dew its just not man enough.

[astronymonkey]

You might get away with the eliptical one as you say,  but it would be worth insulating the back of it with some foam to ensure there is only a small amount of heat loss ..... and allowing most of the heat to go into the metal holder. One of the problems is that these types of holder tend to act like a heat sink so shed any heating that gets pumped into them unless there is some form of insulation.

When I fitted the kendrick it moved the secondary about 3mm further down the tube so I have to significantly change the secondary posittion to move it back up the tube to where it should be...I looks as if you have at least 10mm of room though so that shouldnt be a problem.

Cheers,

[Mike73]

I just got a reply from Jim (in about 10 minutes!!) he said the elliptical is the best way forward.

One of the bonuses I see with the elliptical is that its the one using the least amount of power (about 10%-20% I think) and sits right next to the mirror in a similar way to my current heater does. If I was using my 16" for planets or the moon even this small amount of heat would bother me but for DSO's it should be ok.

Anyway....I've completely sidetracked from your original base thread but thanks for the advice.

[stash_old]

Hi james,

Yes the gemred encoders are hard to find but I was lucky enough to find someone on here who had one to sell which was really helpful.

one of the alternatives I had considered was to use the encoders from a digital protractor / angle finder which you can get for arount £30 but I never went down that route as the gemred became available.

cheers

Try this for your gemred remote encoder  http://www.ebay.co.uk/itm/Remote-Display-Angle-Sensor-Encoder-with-Shaft-for-Rotary-Table-Dividing-Head-/390837006581?pt=UK_Measuring_Tools_Levels&hash=item5affb370f5 

[stash_old]

forgot to add http://www.allendale-stores.co.uk/rotary-angle-encoder-and-remote-display-with-a-6mm-diameter-shaft.html?ref=1 same thing direct and cheaper(delivery?)

[JED-E3]

Try this for your gemred remote encoder  http://www.ebay.co.uk/itm/Remote-Display-Angle-Sensor-Encoder-with-Shaft-for-Rotary-Table-Dividing-Head-/390837006581?pt=UK_Measuring_Tools_Levels&hash=item5affb370f5

That is an excellent find, thank you sir, order placed. I went with the ebay one since the price was basically the same with postage added.

It looks like I have a nice little project for the weekend.

Cheers,

James.

[stash_old]

That is an excellent find, thank you sir, order placed. I went with the ebay one since the price was basically the same with postage added.

It looks like I have a nice little project for the weekend.

Cheers,

James.

James ,No problem let me know how it goes - presently use std no usb version (from same site) so would be interested to know if it "does the job" - If it does then two would be good one for each axis :-)

[astronymonkey]

forgot to add http://www.allendale-stores.co.uk/rotary-angle-encoder-and-remote-display-with-a-6mm-diameter-shaft.html?ref=1 same thing direct and cheaper(delivery?)

great find stash. These have been out of stock everywhere for ages so its good to see them appearing again.

I wouldnt bother with using one for both axis though as the wixey gauge is accrate enough and is self contained so doesnt need installing in any way. There would be benefits though if you didnt want to have both readouts at the eyepiece end as the gemred can have its readouts located remotely ie on a stalk to make them easier to read.

thanks for the link

Cheers

[stash_old]

great find stash. These have been out of stock everywhere for ages so its good to see them appearing again.

I wouldnt bother with using one for both axis though as the wixey gauge is accrate enough and is self contained so doesnt need installing in any way. There would be benefits though if you didnt want to have both readouts at the eyepiece end as the gemred can have its readouts located remotely ie on a stalk to make them easier to read.

thanks for the link

Cheers

Sorry but does that mean the USB version will read and display the encoder AND ,if positioned and set correctley, still display the angle of the Wixey itself - sorry if that a "thick" question. Just thought the USB/Encoder version just showed the encoder details only.

[astronymonkey]

You would need two systems working side by side....

1. Wixey angle gauge which is magnetic and sits on the top tube. This has ist own built in tilt gauge which is accurate to 0.1degree so once levelled it will read the elevation angle of the scope.So no messy wires, just a simple stand alone unit - like a mini digital spirit level.

2. Gemred, which has a rotary encoder and a separate display module which is connected using an RJ45 lead (so you can get a shorter or longer lead to suit). This needs to have its encoder shaft linked to read the rotation angle of the base relative to the ground board then the lead goes up to where you have the readout.

Both the wixey and the gemered display module use the same housing so when they sit side by side they look ok and one reads the declination angle and the other reads the azimuth angle. The only difference is the gemred has a lead that goes down to the encoder on the groundboard.

There are options for taking this further but they are way beyond my electrical skills...

1. the wixey could be stripped down to give a remote tilt sensor, connected to its display via its own RJ45 lead.

or

2. fit a dual display of some type to the wixey to allow the encoder to connect to that and show the encoder angle as well as the tilt.

Cheers