First test of Train-Track on LB 16"

[jarbi]

Hi Everyone,

After one month waiting my JMI order has finally arrived: the Alt-Azimut tracking system for the 16" Lightbridge. It has no computerized part to decide tracking speed on the two axes, but has a nicely designed hand controller. With this one you can slew on both axes with the speed of 8x sidereal rate, and two knobs for setting the tracking speed when pointing to a specific object.

It was very well documented to guide me through the installation, didn't take more than an hour. I will post some pictures here this evening.

A small warning to future users: it has a little design flaw needs to be fixed by yourself.. Namely, you need to install two new brackets with metal rollers on each side of the rock box ( leaning on the side panels), in order to lift up the scope and make the altitude movement much more smooth. The flaw is: these brackets didn't lift up the scope. The rollers were just touching the two aluminium cilinders, but didn't take over the weight . I needed to place metal washers under the "shoulder" of the brackets, to make them sitting about 2mm higher. That did the trick !

Pictures with more details of my last evening test session will follow soon,

cheers,

Janos

[Doc]

Looking forward to this Janos.

[calibos]

Me too

I fitted my TNT do do preliminary tests before removing it. We should compare notes Janos

From my preliminary testing I came to the conclusion that a carefully balanced scope is as important as ever. There was quite a bit of backlash in Altitude when engaging and disengaging the alt motor. I then realised that I had removed the Finderscope but had not rebalanced the scope, ie removed some counterweight from the back. Once I did this the backlash was reduced. What was happening was with the scope back heavy once the motor stopped the scope would try to rise until the alt drive brakes friction stopped it. ie a bit of lateral play in the brake pads. Ditto when starting the motor. No movement visible in the eyepiece till the brakes lateral play went the other way and finally gripped. One could resolve this without resorting to perfect balance by fully tightening the TNT's friction brake but then one loses the benefit of clutchless tracking and smoother push-to motions.

Once I had perfectly balanced this major source of backlash disappeared but there was still some in evidence while there was no hesitancy in azimuth. (after I fixed that too). I think I have a solution to the remaining alt backlash though. I think there may some play in the tangent arm slot where it slides over the button knob. ie the thing that moves along the threaded rod. What I mean is that when moving the scope in alt one way the drive button thingie is pushing against the tangent arm which in turn turns the scopes alt bearing. But because the slot in the arm is ever so slightly wider than the button, when you move the scope in the opposite direction in ALT there is a second or two before the button starts pushing against the other side of the tangent arm slot.

I think a good workaround to remove this slop/backlash is to cut two strips of a 2 Litre plastic milk container about 2 cm wide. and wrap and glue them on each side of the slot which would filll in this small gap and mean the button was pushing against the tangent arm instantaneously.

The plastic from those 2L milk jugs is the jack of all trades in scope circles. Its the poormans teflon. Has been used to make freer azimuth movement on many scopes by using it as a low friction/stiction centre azimuth bearing pad, and the latest use for it is as a disc over your secondary mirror holder which stops your secondary screws digging into the secondary holder and allows much finer more precise secondary adjustments.

Our use of it is as a low friction filler of the slot to make the button a tighter fit in the slot so it starts pushing the tangent arm immediately.

As for Azimuth, I had to move the 'piano wire' tension screw further back than recommended to get the azimuth drive wheels to grip the groundboard rim better and also had to adjust the axle along the drive shafts to get more surface area of the drive wheel tyres to contact the groundboard rim. Azimuth motion was then instantaneous.

I did not have the problem of the TNT roller bearings not taking the weight of the scope. Do you also have a teflon/ebonystar alt bearing mod fitted or particularily thick felt still on the alt base slots?

Obviously I still reserve judgement till I have refitted it with my modifications and perform some thorough testing under the stars but don't think I am rubbishing the TNT or complaining that I had to do some of my own tweaks to it to get it to perform satisfactorily. After all, its a simple device and it cost a fraction of the cost of the servocats and dob drivers of the world.

[jarbi]

Hi again,

I think Calibos has mentioned a number of important things, thanks for that. but promise is a promise, so hier it goes.

After assembling the TNT I took out the scope and switched on the hand controller. I dropped in the 13mm Ethos and pointed to Castor to try how to slew and how to do tracking. First tried slewing on both axes on both directions - the scope responded quiet quickly and I didn't see any resonance on the image. It was an obvious delay, caused by the friction-driven connection between the axes and the motor drive. I was also thinking about to tighten the piano string for increased friction, but it would lead more rough AZ movement when nudging the scope manually I think. Everyone needs to find a convenient balance between too much 'backslash' and too difficult AZ movement.

Altitude movement was pretty good with this setup, because I have an extra 2.5 kg counterweight attached on the tube ( see foto ), and this balances the finder and hevay ocular well. I have done the same test with the Baader binoviewer with the coma corrector attached - much heavier. Than I had some trouble to move upwards in altitude.

Tracking was in both case possible, but Calibos has right: the scope is now much more sensitive for balance, caused by the altitude rollers.

Talking about these rollers, you can see my quick solution to lift them up with (half)washers, I think I will leave it like this, just will paint them black. I have felt on the altitude base slots, but it is very thin. TNT should have taken in regard that people wil not tear it off for installing the altitude rollers.

I tested slew and tracking on Saturnus with an 16mm eyepiece + 3x Barlow - movement was still smooth and reasonably good tracking. I could easily set up the correct tracking speed to keep Saturn 3-4 minutes long in the eyepiece. As you see on the picture of the hand controller there are nice handgrips on the knobs to set the tracking speed.

The instability of the tracking speed comes from the variation of friction forth, mostly on AZ. . I will not adjust the tangent arm yet, but thanks again Calibos for your idea's.

All in all, after spending two nights outside using TNT I don't regret any cent of the price. Keeping the convenience to move the scope manually any moment, you can decide tracking/slewing any moment. I am looking forward to do a whole night with this setup hopefully soon :-).

cheers,

Janos

[albedo0.39]

Interesting set up (welcome to SGL BTW)... I'm interested on several counts. Firstly, I'm about to get a 16" LB so this is clearly a hot topic. Secondly, I run the co. that has just completed the motion system for sliding roof of the the Centre Court at Wimbledon. I've been in the business of precision Drives, motors, and controls as a profession for ~ 25years and I have in my mind a VERY different idea on how to automate the LB dob.

Fact is, it would involve some pretty tasty (industrial) kit, but I'm just looking at the TNT and others to see how they do it first.

Perhaps [and off this thread] I could discuss, but until my ideas are formed, I'd be interested to see how your scope works in real life.

Again, welcome.

[calibos]

Hey Steve,

You can send your prototypes to myself and Janos to test!!

As well as the TNT, have a look at Stellarcats Standard servocat motor setup in terms of the way it can be setup to directly drive the bearings in ALT AZ and in the case of some ATM scopes and stellarcats specific 16" Lightbridge version with the motors connected to pulleys and drive wheels and toothed belts. Also look up the Dob Driver II system.

In terms of dob drives though, the motors and how they interfeace with the bearings is not really the hard part. The hard part is the computer control that calculates the correct motor speed for automatic accurate tracking in any part of the sky.

The reason the TNT is so cheap is that it does away with the microprocessor control altogether. With the TNT one tracks by manually setting the speed of the motors by adjusting their speed till drift in the eye piece is cancelled out in both axis.

While the TNT's duration of tracking is limited by the finite length of travel of the tangent arm on the threaded rod before re-setting the arm it is as much limited to keeping objects in the EP for 10 minutes by the fact that adjusting the speeds of the motors once manually is basically defining a straight line track in the sky. As we know stars tracks are arcs around the celestial pole so obviously after about 10 minutes the arc carries the object off our straight line track and out of the FOV whereupon we have to manually re-adjust the motor speeds again.

Ultimately I may end up biting the bullet and handing over the 1800 dollars for a servocat/argonavis combo for my LB. (it just seems wrong to spend more on the drives than the scope cost however ) But first I thought I would give a 500 euro solution a try first, ie the 450 euro TNT and my 50 euro Orion Intelliscope DSC mod. It might be all the tracking and DSC performance I'll ever need, so I thought it best to try it first before spending the big bucks for performance I might not need.

[calibos]

Janos,

Interesting observation. Your AZ motors directly drive the rubber tyred drive wheels. I got my TNT about a month ago and while I have the same motors , they are mounted on their sides and connected to a little gearbox to which the drive wheel axles are attached. I wonder why this difference?

[jarbi]

Janos,

Interesting observation. Your AZ motors directly drive the rubber tyred drive wheels. I got my TNT about a month ago and while I have the same motors , they are mounted on their sides and connected to a little gearbox to which the drive wheel axles are attached. I wonder why this difference?

Calibos,

Can you post a photo of your AZ drive assembly ? I am wondering also why is it different. The way I received it was the only one I saw on their website.

[johninderby]

Before I sold my LB 16" and replaced it with an OO dob I looked into the Train-n-Track and thought it was pretty good for the price. Apparently it takes a bit of practice to keep the motor speed adjusted correctly, but once that's accomplished it tracks quite well but it's main limitation is the length of time it will track before it has to be reset and balance of the tube is critical. However when you consider it costs a small fraction of a ServoCAT system it's still a great buy.

For the LB 16" it would be the ServoCAT Jr. system. The Az ground board (you would need the ServoCAT one) is driven directly by a drive roller but the Alt is by a belt drive. The Az drive can be released for manual movement by moving the clamping lever that pulls the motor unit away from the ground board. The Alt drive toggle clamp when released slackens off the belt so that the scope can be moved manually in Alt without having to disconnect anything. Tube balance isn't too critical as the ServoCAT drive units have so much power that a few pounds of imbalance won't be noticed.

The ServoCAT Jr's computer tracks on it's own with a few other functions (spiral search etc.) built in and has it's own encoders built into the drive units and doesn't need an Argo Navis if you just want tracking. You do need An Argo Navis with high res encoders or a Sky Commander however if you do want GOTO.

John

[calibos]

I was expecting mine to look like yours too Janos. Then I figured maybe it was an updated design to solve some issue, but why then did you get the version pictured on the website which you ordered and recieved a month or two after me?

Heres the pic, I am going to email it to JMI with a picture of yours if you don't mind and ask them why they are different. There is actually some gear slop in my left motor. Didn't notice anything at the eyepiece but if my other motor developed gear slop too then I would definately start seeing backlash or hesitancy in the eyepiece.

[calibos]

Before I sold my LB 16" and replaced it with an OO dob I looked into the Train-n-Track and thought it was pretty good for the price. Apparently it takes a bit of practice to keep the motor speed adjusted correctly, but once that's accomplished it tracks quite well but it's main limitation is the length of time it will track before it has to be reset and balance of the tube is critical. However when you consider it costs a small fraction of a ServoCAT system it's still a great buy.

For the LB 16" it would be the ServoCAT Jr. system. The Az ground board (you would need the ServoCAT one) is driven directly by a drive roller but the Alt is by a belt drive. The Az drive can be released for manual movement by moving the clamping lever that pulls the motor unit away from the ground board. The Alt drive toggle clamp when released slackens off the belt so that the scope can be moved manually in Alt without having to disconnect anything. Tube balance isn't too critical as the ServoCAT drive units have so much power that a few pounds of imbalance won't be noticed.

The ServoCAT Jr's computer tracks on it's own with a few other functions (spiral search etc.) built in and has it's own encoders built into the drive units and doesn't need an Argo Navis if you just want tracking. You do need An Argo Navis with high res encoders or a Sky Commander however if you do want GOTO.

John

John,

You actually have a hybrid of the two on your OO14. You have the servocat jnr az motor setup but the Lightbridge specific servocat alt motor setup. The Lightbridge specific servocat is cheaper than the Jnr and both axes are driven with those perspex discs and belts. The Lightbridges groundboard and lazy susan are not replaced, in fact the lightbridge specific servocat can't actually work without the original groundboard and lazy susan.

[johninderby]

You can use the ServoCAT groundboard with the LB 16" for a more positive drive if you want to. It fits in-between the LB standard groundboard and the base (screwed down onto the standard groundboard), then the drive unit roller fits through a hole in LB base, but as you say it is a bit more expensive than the standard system. That's the great thing about the ServoCAT system, it can be customized in any you want.

John

[calibos]

You can use the ServoCAT groundboard with the LB 16" for a more positive drive if you want to. It fits in-between the LB standard groundboard and the base (screwed down onto the standard groundboard), then the drive unit roller fits through a hole in LB base, but as you say it is a bit more expensive than the standard system. That's the great thing about the ServoCAT system, it can be customized in any you want.

John

I probably would be prepared to pay the extra for the way you did it John now that I think of it. No worries about tension on the belt or stretching the belt etc and with the servocat groundboard one could utilise the powered groundboard option which is not possible with the Lightbridge specific version, to get the battery out of the rocker box. I am limited to an onboard 26ah to run all my 12v devices and 8!! dewstrips. The sky would be the limit in terms of Amp Hours if I could implement a powered groundboard.

[jarbi]

I was expecting mine to look like yours too Janos. Then I figured maybe it was an updated design to solve some issue, but why then did you get the version pictured on the website which you ordered and recieved a month or two after me?

Heres the pic, I am going to email it to JMI with a picture of yours if you don't mind and ask them why they are different. There is actually some gear slop in my left motor. Didn't notice anything at the eyepiece but if my other motor developed gear slop too then I would definately start seeing backlash or hesitancy in the eyepiece.

Calibos, please go ahead and ask JMI, I think you would also be more pleased with the version I have.

cheers,

Janos

[calibos]

Jim Burr from JMI replied today. He said they had run out of the 22,000:1 gear reduction version for my production run and they used external gear reduction gearboxes to step down the motors they did have in stock.

TBH azimuth is fine at the moment even if one motor has a bit of slop in the gears so functionally this slightly bodged version makes klittle functional difference assuming the other gearbox doesn't develope gear slop. I might even be able to get rid ogf the slop by opening up the gearbox and tightening something or other. But putting all that aside, whether it affects the functioning of the unit at all, my motor configuration just looks ugly and for that reason alone I would nearly demand a replacement. Haven't decided what to do.

Jim didn't say it in so many words, but the vibe I got from the email was that if I asked for a replacement based on aesthetics I would be told NO but that they would of course rectify any problem with regard to the functioning of the motors.

Normally I wouldn't care about the aesthetics either but I have put so much work into this whole scope in terms of aesthetics that I don't want to ruin it with a big ugly motor sticking out the back. ie Your motors look like they were designed to be that way whereas my motors look like a bodge job.

All will become clear when I unveil the scope. Actually now that I think of that, this might actually be the method I use to persuade JMI to replace a functionally OK but aesthetically ugly part despite the letter of the law not compelling them to. ie I will have a lot of JMI product on the scope, (TNT, Transport Kit, Counterweights, Shroud) and its going to be a very unique beautiful example of a Lightbridge.

I can say,

A - "here is the reason I don't want an ugly TNT motor configuration"

B - "I have spent a fortune on JMI proiducts"

C - "Don't you want me to help promote JMI products with this Beautful Lightbridge covered in head to toe with them which will be the talk of many dob/reflector forums"

[calibos]

Just had another look at the az motor assembly. Doesn't look too bad I suppose. I think I'll leave it and only ask for a replacement in the 'standard' configuration if it doesn't work right.