18.1.17

AWR Intelligent Goto Drive System Pt.5. Worm housing requirements.

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Both Beacon Hill worms in their profiled 'housings' are shown alongside with the larger, 34t timing pulleys fitted. Note how the worm size and pitch have to match its own particular wormwheel. The 11" wheel worm is in the foreground with the 8" wheel worm behind.

The number of teeth [287] remains constant. While the circumference of the wormwheel sets the tooth [or screw] pitch. Only specific wheel diameters/circumferences will produce teeth of a useful pitch which can be actually be cut as a "screw thread" for the matching worm.

A worm is rather like a section of screw thread whose diameter must also match the required pitch of its wormwheel. A completely random choice of [odd] pitch would make the worm all but impossible to produce in a normal screw-cutting lathe. A worm is not a normal [i.e. nuts and bolts] screw thread. Because the tops and bottoms are flattened in the form of an ACME thread. These threads are commonly used for vices, G-cramps [C-clamps] and other very heavily loaded screwed devices.

Only the flanks [sides] of the teeth do the driving and the worm must not bottom in the wheel teeth. The two components must have just enough clearance to avoid backlash. Without any free rotary movement of the wormwheel.

AWR makes great play of the need for very stiff worm supports to avoid all flexure. If the bracketry should flex then it will also unwind again when the drive load is removed. Leading to lost motion or overshoot during Goto maneuvers.

The worm brackets must also be firmly fixed with suitably large bolts. Or the drive power available will dislodge the worm housings. Meanwhile the worm housings need fine, radial screw adjustment towards and away from the circumference of the wormwheels. There is really only one ideal position for a worm nestled against its matching wormwheel. It must be square to the wheel or the threads and teeth will not allow the necessarily fine adjustment needed.

The pulley to worm shaft fixing screws must lodge onto small flats or dimples on the worm shaft to avoid them loosening over time. The tiny grub screws provided might be better replaced with stainless steel, hex socket head screws. The worm housing bearings can also be prevented from linear movement. The tiny grub screw on top of the bearing housing is hardly adequate. Over-tightening can easily lock the bearing against rotation! An outboard plate at each end of the housing will prevent bearing shift.

Wormwheel and worm mock-up on oak blocks.The arrows show the positions of the radial nylon plugs which provide the slipping clutch. Grubs screws provide the adjustment of pressure.

I originally made 5mm [1/5"] worm support plates but these could still flex. A later find of a long length of scrap, 10mm aluminium [also 6" wide] offered a much stiffer alternative.

The availability of scrap aluminium is not an ideal design parameter for telescope making but one is always incredibly grateful for whatever turns up. One should never try to haggle or the scrap dealer will quickly lose interest in helping the oddball.

I have been extraordinarily lucky in finding enough 10mm and 20mm plate in good condition at a single scrap merchant. Alas, finding suitably heavy alloy angle has resisted all my repeated visits. Metals can be bought on eBay UK and DE  but the Danish metal stockholders will not deal with private customers. Trying to buy 4mm plate from a local engineering firm proved very costly after they had guillotined a couple of modest pieces to size. A return visit provided no suitably heavy angle for worm support.

The new 10mm support plates will still be trapped between the bearings housings and the axes heavy flange bearings. The four equally heavy 16mm, [~3/4"] corner studs [all threads] will prevent all movement.

It will be up to me to provide finely adjustable but immovable support for the worm housings. An earlier plan to use solid oak support blocks was ditched when the blocks changed their dimensions with moisture content. They could also be compressed by their fixing bolts. After carefully setting up the fit between worm and wheel by feel alone I would come back and find the friction or backlash had changed. Not a good start.

So the supporting material must be made entirely of metal and of adequate cross section to avoid all flexure. The problem is that there is quite a space to make up between the 10mm support plates and the bases of the worm housings. As can be seen by the height of the oak blocks. More on this later.

 
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17.1.17

AWR Intelligent Goto Drive System Pt.4 Intelligent Handset V speed.

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A 5m long yellow cable is a Cat6 network cable is provided for connection of the IH to the Microstep drive box. Allowing plenty of freedom to move around the telescope. Or even reach the workshop/warm room. If only I had one! It reached 25F or -4C inside the workshop a couple of days ago and the entire mounting is still sparkling with hoar frost!

The cables to the stepper motors are also very generous in length and all have latched plugs and sockets. Though I do feel a cable anchor at each end of the IH cable might be useful. There is a guard on each end of the cable to stop accidental contact with the little latching/release tabs. However, the vulnerability of this cable in the dark places rather a lot of trust in the relatively fragile little plugs.

A second socket on the base of the IH provides a connection to a PC for point and click control using Stellarium or similar 'planetarium' software. Which is a very useful provision because it saves a further length of cable to reach the PC from the drive box. BTW. Stellarium may need a special download from their website for telescope click and Goto control. Later editions have a small telescope image on the bottom line to show the telescope control is lying dormant and ready to be resuscitated.  

The Intelligent Handset screen on first power-up. BUT: See note in BOLD above. The AWR initial copyright screen is available by pressing F4 from the normal [default] screen shown. The text appears truly black to my naked eye. The camera lies again! Note how the bottom row of drive instructions in the display changes to lower case when active. [After F1, 2, 3 & 4 button selections just below the screen.]

King refers to standard [stellar] drive rate.
--- Shows a code letter W, P or C depending on what is happening.
LST is Local Sidereal Time.

SITE A is one of four possible locations. Lat & Long are easily stored [to the nearest second of arc] to avoid repeatedly entering locations by hand if regular but different observing sites are used. Many amateurs must escape from light pollution at their own home. So they drive out into the countryside to a familiar spot free of extraneous light. AWR can still work even in the Outback with a properly fused 12V battery. Most car and motorcycle batteries can easily fry an egg if short circuited! Both leads to the AWR Microstep box terminals should be fused. AWR recommends inline car fuses of suitable ratings.

I like the way the text almost fills the small screen rather than demanding a microscope to read undersized text. Old age and reading glasses often come hand in hand. Needing glasses at the telescope, just to read the screen, would probably wear thin after a while. I think I shall be able manage without. Though a square [plastic?] magnifying glass could be taped over the screen for easier legibility if it proves necessary in practice. Luckily I only have one dioptre of reading error so I am hoping the lit screen is easily legible when lit.

I captured a couple of short videos to show the huge differences in drive speed [i.e. stepper motor rotation] but they [the videos] were much too amateurish [i.e. shaky] to share online. First I need to arrange both motors and the full IH in simultaneous view with the camera on a steady tripod. Capturing the screen readout will need some care to be useful to curious YT viewers. Mental rehearsal will help to avoid wasting the valuable time of the viewer. Far too many YT video makers waste huge chunks of viewer's time where nothing useful or interesting is happening on screen.

I would guess [very roughly] that the fastest [Slew] motor shaft speed is about 90rpm. It is slightly too fast  to count full rotations by the usual "one thousand, two thousand," verbal system without hurrying unduly.

The 14/34 pulleys and belt provide a reduction of 2.4:1. So say ~ 38rpm is applied to the worm shaft. 38/287 = ~0.13rpm on the mounting's axes.  0.13/60x360 = 0.8 degrees per second. AWR claims their system should slew at about half a degree per second. To move the telescope from fully East to West, over a full 180 degrees, would take between two and three minutes. Though remember that this figure is is based on a very rudimentary rpm count. Only an active system with a real telescope would indicate the correct speed of a slew. Those who want faster slews can obtain them from AWR, at a price, for a 24Volt 'turbo' system.

Lest ye consider the suggested slew speeds pedestrian: It should always be remembered that an accurate Goto will save an enormous amount of the observer's time in not having to search for an object. Particularly a dim one. In fact Goto may be the only way for some observers to find many objects in light polluted conditions. Including full moon. Though not usually as a Goto target. Unless you live in Beijing! Moon? What moon? 😵

 
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16.1.17

AWR Intelligent Goto Drive System Pt.3: First Test!

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AWR Technology (Astronomy - Electronics, Motors, GOTO drives, Sidereal Clocks, Display Units)

Since all the sockets are clearly marked and all the cable plugs 'handed' I assembled the entire system "instructions unaided" before switching on. Though first I had to find a  continental mains plug. Since only a 13A UK square pin mains plug cable was provided. No big deal. The AWR power supply uses the common figure-of-8 plug on the mains input.

Using low  voltages for the drive system and motors avoids having mains out at the damp-exposed telescope. The PS can be housed safely indoors or at least in the shelter of a shed or warm room. Though this will require an ample, low voltage extension cable with shielded banana plugs and sockets. As supplied, the power supply will be out beside the telescope with the AWR drive system itself. An imaging/Goto PC and monitor are likely to be under shelter unless a laptop is used. It seems logical to keep the only mains voltage item well protected too. It is clearly marked for "Indoor Use." Running an extra few yards of several amps at 12V DC will require something better than the skinniest cable available to avoid voltage drop from resistance. Speaker cables often use banana plugs but the live pins must not be touched together. AWR has overcome this problem with the telescopically shielded plugs. The other end of the low voltage cable is anchored in the sealed power supply box so cannot easily be extended.

A red diode shows the Microstep Drive Box has power. While a green diode is provided on the power supply. 

Whoops! I should have read the instructions on the AWR website. I was supposed to plug the IH [Intelligent Handset] in after power up to get the initial copyright screen. I later discovered that pressing F4 produced the copyright screen on demand. The system is supposed to start tracking normally once the Copyright screen has changed to default. 

To avoid further confusion The Handbook, referred to on the AWR website, is also the IDS Manual. A downloadable, 59 page guide to using the AWR drive system. 

For normal use the IDS Manual acts as a useful reference but the Intelligent Handset is remarkably logical in its menus. Provided the telescope mounting is properly set up first a reasonably savvy user should be underway in using Goto control in no time.  

All seemed to be well on first power up except for the remarkably slow rotation and quietness of the stepper motors to directional button presses.  For some reason I had imagined they would literally whizz [scream?] round. Well, all telescope drive motors scream in the YT videos! 😊

 The small fans on the Resistance dropper box are rather noisy when close-to. These are to dump unwanted heat. Suggesting they will require some thought in siting the electronic equipment to avoid thermal effects on the telescope image. I am now imagining a flexible hose to warm the poor [old] observer at the telescope. Though I am probably exaggerating the free heat available. Probably a northerly airflow will suffice to avoid heat plumes. 😎

Both motors will happily run simultaneously and in opposite directions.  It may be that when following Goto instructions the motors will spin faster? Remember that the motor speed is further reduced by 2.4:1 the pulleys and then by a further 287 times by the worm and wheel. From memory, slew speeds up to half a degree a second are claimed for the system. With controlled acceleration and braking no less. Probably a good idea when swinging a long and heavy telescope across the heavens. Touching any one of the direction control buttons will stop a slew before any unwary visitor is beheaded or the priceless APO refractor dewshield crashes into the dome! Common sense suggests that a new user sets the limits and horizon parameters before loosing his telescope on a Goto tour in a confined space!

IMPORTANT SUN NOTE: A daylight Goto may easily sweep across the sun! [What sun?] Since the actual path of a Goto slew cannot be predicted the OTA should be capped during daylight slews. Or, have a full aperture solar filter fixed safely in place in daylight. For the same reason: Never leave a telescope unattended in daylight if children could ever get near enough to blind themselves at the eyepiece! Do not assume they can not get in! We returned home one day to find several of the neighbour's children enjoying a guided tour of our closed rural garden by a 7 year old. Including toddlers excited by the fish in the goldfish pond! We put a padlock on the gate after that.

Following a [forced] lunch break a second drive test followed. Proving that Slew is the fastest mode and the others are very much slower. Literally crawling round [at different speeds] to allow Guiding, Centering and Moving without the danger of overshoot at high magnifications. All perfectly logical if you think about it for a moment. It would require quite some patience to count the number of motor rpm of the other drive rates: [Guide, Center and Move.] It is quite amazing and certainly impressive to see a motor shaft rotating so incredibly slowly for the first time! No intermediate gearboxes either.

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AWR Intelligent Goto Drive systen: Pt.2: What's in the box?

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I have split the original post to avoid long download times.

One end of the Microstep Drive Box with sockets for the stepper motor cables, Resistance Box [unmarked 12 pins lower socket] and for the 12V 7A power supply.

And, the other end, with AWR logo and sockets for the Intelligent handset [IH], Simple handset [center] and automatic guider connection. [CCD1.] 

The 7A 12V DC power supply with insulated, telescopic banana[?] plugs.

All the necessary cables are provided for connecting the entire system.














Sanyo Denki stepper motor with latched cable attached. These motors are so heavy there can't be much room left for any "fresh air" inside. 'Solid' is probably the best term.

Loose P-clips are provided for cable strain relief once the motors are safely mounted to sturdy brackets


The shaft end where the small, toothed, drive pulley will be fitted.

The loose green cable is presumably for earthing.







5mm pitch x 10mm wide timing belts and the 14:34 pulleys provide a 2.4:1 reduction in worm rotation speed from the stepper motors to the worm shafts. While simultaneously increasing torque by a similar amount. This means slower slews but more power for moving and controlling heavier OTAs or overcoming mounting/wormwheel friction/OTA imbalances.  All of these should, of course, be minimized to provide maximum slew performance during Goto instructions from these sophisticated drive systems.

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AWR Intelligent Goto Drive System. Pt.1 What's in the box?


For those considering an AWR Goto Drive system I offer the following user experience:
Note that I am just another private customer with no other commercial connection to AWR. So WYSIWYG, warts and all. There is so little written about AWR drive systems online that I thought I'd share my own thoughts. I shall add some YT videos when I have something to show.

Normally I add images to my blogs in any size I consider 'cosmetically' attractive. However, in the interests of those still connected to the 'Interweb' by a very long piece of damp string I have kept the many images smaller than usual. This makes the text layout unusually untidy. You'll just have to blame the cheapskates in power who won't give their citizens a 'proper' Internet service but can still afford "defense" spending. I have enjoyed a reliable, 57/57Mbps, optical fiber connection for some years. So tend to forget that in some backward countries, like the US, UK and Australia, there are still those much less fortunate. My sincere commiserations.  

Meanwhile, back in darkest, rural Denmark: The substantial 36 x 28 x 18cm, 8kg cardboard box contained the following items: [All well packed.]

Fit and finish is all very tidy. With security zip ties on many of the plug:cable terminations. The plugs and sockets are all easy to fit. Plug removal is as simple as pressing the locking side 'bars' inwards. There is bound to be a technical term for these: Latches? The only likely confusion is reversing the cables between the RA and Dec motors. Easily fixed simply by swapping the cables over. The stepper motors are identical.

Note: In the image I have added a 30cm [12"] transparent rule on top of the main components for scale.

List:
IH2. Intelligent [Goto] handset.
Microstep drive box.
Resistance dropper box with twin, serial fans for cooling.
12V DC 7A Edac power supply.
Two [remarkably heavy] stepper motors 210.
Umpteen cables.
Two sets of reduction pulleys and AT5 toothed belts in 5mm pitch x 1cm width.
Pulley ratios of 14:34t were supplied. 14:32 is optional for lighter loads.
Lower gears provide more power [torque] but slower slews. I shan't complain and swapping pulley sizes is easy enough if I discover ample power for faster slews with my ~35-40lb OTAs.

4 sheets of A4 paper: Invoice, Payment details, factory construction sheet with specs. Drawing of standard pulley set-up. No instructions, at all, were provided. [The AWR website simply says to assemble and test.] Anybody who can connect up a smart TV and Hifi System should have no problem.

A downloadable 'Handbook' is listed on the AWR website but the link failed to respond with a download in W10. So look for the IDS Manual link instead. Which is exactly the same thing as the 59 page Handbook but as a downloadable PDF file.

The 'Goto' Intelligent handset [IH2] provides direct telescope point and drive control with various drive rates and is programmable by the [advanced?] user.

It also contains various sky catalogues and menu filters for direct input Goto instructions. Alternative object catalogues are available for download.

The central four buttons provide the familiar direction controls. E, W, N & S on an equatorial mounting. The Mode/Menu buttons F1, F2, F3 &F4 decide the speed of motor rotation and therefore telescope movement via the slow motion, 287:1 worm drives.

The IH handset is larger than I had imagined but this is arguably more 'handy' when wearing gloves at the telescope. Nor is it so easy to lose in the dark! A lit screen provides position RA & Dec and/or other information depending on the selected Mode/Menu. AWR prefers the term Menu but I like Mode better for changed sets of actions or instructions. Suit yourselves. You will anyway. 

Point and click Goto, via a PC or laptop [or tablet?] is available via popular Planetarium software.

A printable IH instruction 'tree' [Menu] is available on the AWR website for all the normal button presses. The IH can even be fixed to a surface near the telescope or hooked into a bracket with 'ears'  if it is not to be handheld. A docking station + power supply is available at extra cost to keep the timekeeping crystal cosy [and more accurate.] A button cell provides internal power to the crystal but not its oven.

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