16in Lightbridge exterior plywood dob base build

[astronymonkey]

Since buying my 16 inch lightbridage ive haad some great views but have always been a little hindered with the size othe base. The base  foes fit through a normal door but it is bulky and also very heavy . In addition to this its made of chipboard which is prone to water damage in the field and despite being very careful I do have one or two stained marks on the very bottom of the base which doesnt effect performance but has annoyed me as Ive been so careful.

So, Ive planned to make a replacement base using 18mm external plywood at about £35 for a single 8x4 sheet.

Using google sketch up I come up with an octagonal desugn which will allow me to keep a circular base as I prefer this over the sinpler square based design but it will mean having to cut  22.5degree corner mitres on every upright panel.

Below is a draft of the base showing the position of the lightbridge bottom tube, the key dimension is the 55cm width as this maches the width of the existing base using the current alt bearings. This view is from the front of the base , cut at angles to allow the truss tube to point at the horizon

The shot below shows the back of the base, this shows the cut away which will allow the base to swing

And below shows the side view.

The design will allow for a 65.5cm circular base which is considerably narrower than 80cm of the current base, and Im hoping the final base will be at least a third lighter than the prodcution base.

So today the build began, and so far I have the top box section completed and dry fitted together and the scope swings smoothly without fouling anything which is a relief given the complexity of the design. Next up will be the base boards, and after another dry fitting everything will be glues screwed and braced to make everything very ridgid.

The icing on the cake will be the fitting of a rotary encoder onto the base azimuth bolt shaft to give a digitsl readout , and when paired with a wixey will give a full push-to function.

When I get chance ill post up pics of the build as I go , and hopefully all will be done ready for SGL 9.

Cheers

[swamp thing]

Great project, look forward to seeing it at SGL9 and maybe a little drive of it too

[crashtestdummy]

There's actually a compa y that make a new smaller base for the lightbridge but I don't have the link anymore.you thought about making the altitude bearings bigger while your at it as for me that was a big downside

[astronymonkey]

Hi crash,

ive seen an american company that make them but they are a ridiculous price for what they are. As for the altitude bearings ive never had a problem with them , so im keeping them the same.

cheers

[albedo0.39]

I have had a new base designed and built for me from a well known guy in the Norwich Astronomy Society. It will be with me at SGL. Like you, I wanted to lose weight and also improve the tolerance to damp. I also upgraded both bearing sets to Teflon away from lazy Susan and felt pads.

The movement is now epic, it looks superb... But it's frankly still a bit of a beast. I may remove some of it prior to SGL 9 but not sure.

PM me for pictures...

Rgds

Steve

[iam4208]

Shouldn't this be done during the off season, lol! But seriously, it looks the business.

Sent from my HTC EVO 3D X515m using Tapatalk

[astronymonkey]

Im possibly going to have to make a minor change to make room for the encoder in the base.

At the moment the base box is glued and screwed but can be removed from the base board and raised 5cm to give room under the bottom tube for the encoder. Id taken the height from the original but might not have factored in enough room for the encoder .... easy to sort though.

im going to use the existing lazy susan as it works well and will probably use felt, or the furry half of velcro, for the altitude bearing surface as the felt on the original give a good feel to the movement.

cheers

[astronymonkey]

Heres the build so far ...

[John]

Thats looking nice 

As well as more compact, it should be lighter than the standard LB MDF base. My 12" LB was a real lump to move around, almost put me off 12" dobs for good. No wonder that stock 16" LB owners need wheely bars !

[Rustysplit]

That looks good. Nice and sturdy.

[Beulah]

I've been meaning to do this for a while as I don't like the chipboard base of my Dobsonian.

Great project, I'm going to stay tuned.  

[astronymonkey]

So the build has moved on quite a bit now having finished the azimuth movement by using the lazy susan off the original base. This has turned out to be really smooth and Ive fitted the teflon pad from the original aswell as the lazy suzan was too free movin and the teflon gives a bit more feel to the movement.

For the altitude Ive used felt . This is the way the original was made and once again this seemed to work really well. So after a trip to Hobbycraft I got some self adhesive felt  priced at only 80p for an A4 sheet. These cover the hole of the semicircular altiude suface and work suprisingly well.

Now the tricky bit .... fitting a rotary encoder to the base.

Well I made the base plate with a 10mm hole drilled into it and a M10 nut recessed into the top side. This nut was held in place using epoxy resin meaning when the bolt is threaded through and tightened it is basically fixed to the bottom base plate and wont turn or rotate.

Next was the really tricky part, connecting the M10 thread of the centre bolt to the 6mm shaft on the encoder. Given the degree of accuracy i was after, a direct connection was preferable as a pulley arrangement would mean having to have perfectly matched pulley sizes and the risk from the belt slipping would reduce accuracy. I considered various options and managed to get a 6mm connector with an 8mm blank end , this is the type of connector used for propellers in model boats.

So I was half way there and took a trip to Hawk Fastners in Middlesbrough to see what they had in stock. This place is amazing, its an engineering works that specialised in fittings and if it doesnt have it in stock then they can make it  for you or modify a stock part.

Affter chatting with the worshop manager he decided the quickest and cheapest solution would be to get an M8 connector nut (about an inch long), tap pne end to an M10 female thread, the use a hydraulic press to push the brass fitting into the remaining 8mm end of the connector nut ...... 15mins later I had the desired part in my hand for the total price of £2 !....... yes ...... two quid !

So I went home and the conector joined the centre bolt to the encoder perfectlly.

The next step was to fix the the eocoder to the top base plate, whilst the shaft is held stationary relative to the bottom base plate via the M10 bolt. I therefore fashioned a wooden frame to hold the encoder.....

Once fitted it did a test run of the system by marking the bottom and top base plates, zero the encoder, then spin the base a full revolution. The results were bang on (or within 0.2 degrees) , which with a 204cm circumference of the base is equivalent to 1mm - which is less than the thickness of a the pencil line I used hence the potential 0.2 degree error being down to me !

The only adjustment Ive had to make was to raise the rocker box by 75mm in order to clear the encoder.

So my next steps will be to fit an altitude brake, and then if I have time I'll varnish the base but I may wait until after SGL when I have chance to fully test the new base.

Cheers

[astronymonkey]

At last, all finished. Only varnish to go on but that will be done once field tested at SGL this weekend.

A few pics of the scope on the base , the blue bungee is to hold the battery / jump starter on the front lip of the base to powerthe dew heaters on the eyepiece and behind the secondary..... sorry about the decor and curtains, they were there when we moved in but havent got round to decorating yet, hence the boxes lying around too 

cheers

[Rustysplit]

Good job their 'monkey. I reckon the size of the original base is the main fault with the lb's and SW flexis. Nice and compact now, enjoy!!

[swamp thing]

Yep! Much better.

Nice job

Should put a before pic up for comparison. That looks way more compact

[Daniel-K]

very nice and tidy  if i ever plan on keeping a scope more than a few months id love to do something like this

[astronymonkey]

I managed to finally road test the new base at SGL9 last weekend.

After levelling the base using a bubble level app I'd downloaded onto my tablet i put the tube assembly onto the base and used the daytime moon to calibrate the system.

First I used another app called Mobile Planetarium to find the alt az co-ordinates of the moon and after centreing the moon in the scope I zero'd the wixey and lowed the tube by the 54degrees of elevation which the moon was meant to be at. Once this was done I zero'd the swixey again . To set the azimuh reading I centred the moon again and zero'd the az reading then swung the scope around by 178 degrees which was the Az position at the time according to Mobile plantarium ... the scope should then have been pointing due north so it was Zero'd again.

Having done this basic one star (ok it was one moon) aligment I then went for a challenge of finding Jupiter during the day in full sun.

Using Mobile Observatory I found the alt az coordinates of Jupiter and swung the scope around until there were the readings on the Wixey and Rotary Encoder readouts and was amazed to see Jupiter in all its glory in the eyepiece !

Unfortunately there wasnt chance to try the system again at night due to the cloud but given the success with Jupiter I was really pleased with the system.

The base is also much smaller than the original and ended up 6lb lighter even with the encoder system.

All I need to sort out now is the altitude brake which allowed a bit too much movement for my liking and I also need to varnish the base.

In summary Id say this sort of mod is a great improvement over the standard base, allowing easier transportation and the advantages of a push to system.

Cheers

[quaoar]

Here's some changes I made to my Lightbridge 16, the ArgoNavis and Servocat are real gamechangers.

Cheers

Barry

[astronymonkey]

Hi barry,

nice set up. I'm really see the benefits of a push to system too.

Its nice to be able to starhop as usual but then use the system when things are proving tricky.

by the way, I like the wheels you have !

Cheers

[JED-E3]

It looks like you've done a great job on the base, I find with with my square base it's hard to get close enough to the tube when seated and viewing at high angles, yours looks nice and compact.

I wouldn't mind trying a Gemred rotary encoder on my dobsonian but they seem to be unobtainable now, the only ones I can find for sale are £92 on amazon marketplace, which I think is double the rrp.

James.

[astronymonkey]

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

[quaoar]

Just some pics of my wheel setup. Its a very easy mod to make to any LB and makes a big difference to portability. The wheels stay on all the time, don't get in the way at all and have no effect on the balance. The wheel barrow handles slip on and off through collared eyebolts and the weight of the telescope provides all the necessary friction to move the scope. I'll shut up now and stop hijacking this thread.

[Mike73]

I should be getting my Nexus push to system within a couple weeks, I'II add a thread will loads of pics and my thoughts on it when I install it. May be of some interest to you Astromonkey?

Going a little OT but is that a Kendrick secondary heater you have on your LB?

[astronymonkey]

Hi Quaoar,

Ive been considering adding a wheel barrow handle similar to yours but at the moment the scope needs to be lifted over a step but when we complete some building work I should have a flat exit onto my patio.

I think steve (swampthing ) has a similar system to yours but its totally removable and I think it uses the weight of the scope to keep the wheels in place.

Cheers

[astronymonkey]

I should be getting my Nexus push to system within a couple weeks, I'II add a thread will loads of pics and my thoughts on it when I install it. May be of some interest to you Astromonkey?

Going a little OT but is that a Kendrick secondary heater you have on your LB?

Hi Mike,

yes it would be good to hear how the Nexus install goes. Id be particularly interested in ts accuracy and its alignment system as Im limited to single star so a level base is quite important so Im cosidering adjustable feet of some kind to make this easier.

As for my dew contral, yes I use a kendrick system and on one of my earlier pics you can see the 2inch eyepiece strap wrapped around the truss tube to keep i safe. One of the key things though is the secodary heater I have fitted which is hidden behind the secondary housing. This keeps it  hidden and also makes sure its held as close as possible to the back of the secondary meaning it uses only a small amount of power. Since its been fitted Ive had no problems with dew.

heres a few photos of the fitting of the secondary heater

cheers