EarthLife

Why not buy yourself a printer ? It's very nice having the freedom to print your own parts whenever you like, although 3D printing can (and does) come with much frustration and despair at times

I too have FreeCAD, but prefer to use the free Autodesk 123D Design program, it's GUI and ways of doing things are easier for me I find. Autodesk no longer have it available for download but a quick internet search will produce some download links. If you start using 123D Design then make sure you disable the "Check for updates automatically" option (in preferences) otherwise it tends to sit there doing nothing at times whilst it tries it's hardest to download none existent updates.

You can also do it in openscad (free parametric design program). A ready made design file can be found here .. https://github.com/openscad/MCAD/blob/master/involute_gears.scad Load that into openscad and uncomment the first top bit where it says "Simple Test" to show how to use it. It takes a few seconds for the design to show up in the window but once it does just zoom out until you see the whole gear, then save it as an STL file (or whatever). Can then import it into your usual cad software and use as you like.

One thing you have to be very careful of tracking sky-ward objects during the day time is the Sun !! It would only take a few millisecs to destroy a camera sensor or your eye ball/sight. When using object tracking software that can be avoided by having the tracking software stay well clear of where the Sun is at that time (assuming it knows the current Sun's position and also the telescopes location and pointing). When doing manual day time tracking your eye's and/or camera sensor could very easily be destroyed in a flash. NO 2nd CHANCES !

It's not a difficult thing to do, but finding the software to interface with your camera and mount setup might be. I've done it myself by writing a simple piece of optical tracking software for my camera and mount, it simply tracks an object that appears in view, it tries to keep it centered but smooth tracking is the priority, easy enough once it see's what direction the object moves across the camera image (the frame rate has to be high enough). The difficult bit is to first get the desired plane/object within the telescopes/cameras field of view, once that is done the object tracking software takes over with ease - so long as the object doesn't do sharp 90deg turns like all the imaginary UFO's do

Hi @almcl, notice you're in Telford. If you want someone local to you who would do your prints for you then pop into 3D Printz on Hortonwood, they are open most all week days, it says trade counter but the public are more than welcome, they have printers sitting in the back doing nothing most of the time I think and so will help you out if you wants (Peter the boss). https://3dprintz.co.uk

Although it doesn't apply here, the speed of light does vary for the RF carriers being received by your GPS receiver as the carriers make their way through the atmosphere, the time they take does vary depending on what the atmosphere is doing at the time, the different atmospheric layers slightly alter the speed of light in varying amounts. The RF carriers time of flight measurement is a one way speed of light measurement, it's not a round trip measurement. The GPS satellites take into account the speed of light variations through the atmosphere to allow our little GPS receivers to make as accurate a position calculation as possible. The varying speed of light through our atmosphere is continuously measured by the satellites and ground crew. As we don't live in a vacuum, it doesn't apply to the threads topic really, but GPS receivers are doing measurements based on one way electromagnetic wave transmissions and their slightly varying speed.

One way a reflected electromagnetic wave could travel at a different speed is if it travelled through a different medium (gas etc) whilst on it's way back to what it did on it's way there, but that's not really what's being discussed here (same medium there and backuds).

A very nice episode Martin's a star.

mmmm, a species wanting to spread throughout the galaxy like a virus does not sound like a very nice or intelligent thing to be doing. Lets hope the human race is stopped before we do irreparable harm to other life bearing planets. It's comforting to think that if we ever did physically enter another planets biosphere containing life that their pathogens would literally stop us dead, unfortunately our pathogens would do the same to them mixing lifeforms between different planetary biospheres cannot work, we should have learnt that from our experiences within our own biosphere in years gone by (the colonising centuries).

As they say, "life finds a way". If it can't, then hence Mars, Venus, Mercury and the rest of them. This would be by far a much more desirable thing to achieve (or not, depending on what we'd really find) ..

re: Mars .. I can't see the human race ever being able to make a go of it on a planet sized desert with no atmosphere (1% earth pressure is still basically vacuum) to slow down and burn up 100's of incoming meteorites every day before reaching the ground and no useful magnetic field to provide much needed protection from the sun's radiation when we can't even take care of a ready made paradise perfect for life as we know it here on earth ! re: Venus .. A 400C oven with a level of sulphuric acid / carbon dioxide pressure that means parachutes are not required to land (you float slow enough down to the ground to remain in one piece). You have to be realist with such matters.

The more we think we know about it, the less we know we know Both episodes are a very nice change to all the other nonsense shown on todays TV. The tiny bits (1st episode) are just as big as the big bits (2nd episode), yet most likely hold the answers. The last episode was quite fascinating towards the end what with the paths the galaxies are taking on there journeys and what not. What is the universe really I wonder, and how ? Given our notion of cause and effect, how can the universe actually be, how can something ever pop into 'apparent' existence in the first place, whether it be the universe as we see it or whatever came before it, and before that, etc ... ? it's for sure going to be beyond our tiny and ever so flawed reasoning - for sure. A most unfathomable mystery

£98 for a harmonic drive such as that particular sounds like a good price ! They don't mention backlash levels, but I've seen other manufactures elsewhere state 'zero backlash', which is interesting as I never knew that. DIY'ability, backlash, stiction, simplicity, smoothness, cog'less, linear-torque, reaction speed etc were the reasons I decided on a direct drive, I don't have any experience of using harmonic drives. Robot designers seem to really like them, I'm assuming it's what's used in industrial robot arms. Any level of backlash free gearing makes accurate position sensing easier as well.

One of these steel 130mm dia rings for the coarse scale I think might be nice .. https://www.aliexpress.com/item/32959835235.html

Yes indeed, though I want to ensure that the routines are fast enough to keep up with rotation. If the motors start rotating at a fast rate then the software only has to keep track of the coarse printed graticule scale, it's only when rotation slow down that the firmware will use the sandpaper pattern to fine turn the exact position computation. I'm going to initially use a cheap 360deg plastic protrator as the coarse scale as they tend to have at least 1 line per degree, which is enough to get the position down to say an arc-min with a bit of processing. The protrator will be overlayed on top of a round piece of sandpaper. Here's P600 grit (larger pieces than P1200) .. I just need to pick a suitable image sensor chip (SPI bus or some such serial) that can be configured to take images at a fast rate, a 128*128 pixel sensor should be good to start with I think, together with a fast LED or laser (0.5mW at most) light source as a strobe light for the sensor so that sharp images can be obtained as the motor rotates. So long as I can capture images fast enough to keep track of the coarse line scale it will be fine. If the firmware did loose it's position, it could use the sandpaper to regain absolute position rather than going back to the 360deg index mark. It's really just a basic DSP image processing task.

OK, that's quite big ! Could never justify £6000+ mount for a hobby grade telescope though. Am hoping to create a DIY'able design for around £100'ish for two DD motors and encoders.

Yes that's an outrunner motor (magnets around the outside of the stator). I couldn't decide on whether to do a pancake (disc) or out/in runner. The disc type seemed easier to start with. They do don't they ;)

A short length of 100mm*100mm aluminium tube (around £5) as the support frame (for testing at least) .. Is the axis rod used on mounts normally of a typical diameter ? Obviously the larger the diameter is the stiffer/stronger the axis is, but just wondered if a preferred size is tended to be used.

No don't stop asking questions, by all means ask anything you like, it's how we all learn from each other (a good development engineer never stops learning or asking questions). An up and coming (and serious) problem I see coming our way (quickly too) is the young don't appear to have any interest these days in learning how things work or how to go about doing something ourselves or having any kind of hobbies etc. Skills are being lost at a high rate of knots it seems An example .. The school two of my nephews went too (they are 18 and 21 now I think) had no computers or computer classes for pupils at all, - crazy ! result is that their only experience/learnings of computers is playing on their xbox's and finger twitching on their phones all day long, no science learnt what so ever during the easy learning phase of their lives, they have no real-world or science knowledge at all There's a film I quite like called "Idiocracy" that often comes to mind, a fun film but sadly all too real if we're not careful.

If I use a ras-PI board as the encoder board that shouldn't be a problem. Time will tell, I usually get something going then once I have the code doing exactly what's required I then work on optimization etc to speed it all up. I should think so yes, those effects are actually very slowly changing external events as far as an controller is concerned. We as squashy/squidgy living beings aren't quite so good/quick at reacting to sudden/random changes. Developing new tech/prototypes etc is often quite fascinating/interesting/challenging at times, it's what makes it so. I've been involved with developing cutting edge tech for a few decades now, so this is not really a difficult one to solved.

If the scale is rotary disc then that is kind of calibrated from the start - if a disc has say 360 lines around it, one line per degree, then if it expands/contracts with temperature then it will still only have the same 360 equally spaced lines on it, just slightly different diameter than otherwise, angular resolution remains unaffected. But calibration can be done by following a star through an evening, the stars position will be exact in the sky (they don't tend to go walk abouts), the telescopes position will be static (and known), the position sensors CPU clock will be accurate (GPS time locking is easy - around £8 for a board level GPS receiver and antenna). Using that known data/info from a single night a precise calibration can be done by the software itself., a one time operation (unless you change something).

In actual fact, due to sand paper being unique and fixed along it's entire surface, it can be used on it's own (without a coarse graticule scale alongside it) as an absolute position sensor, an extremely accurate one at that. Once a single run of the strip of sand paper is recorded and learnt by say a neural network (or whatever method is chosen to recognize the unique grit pattern), then by just taking a single image from any point along that strip (or from a circular disc of sandy paper) using the image sensor and feeding that through the image recognition routine (whether that be a neural network or not or a mix of neural and other methods), an exact position can be computed, not just to camera pixel level, but way down in the sub pixel range (as is currently done with image guiding on stars). The coarse printed linear graticule though will be there with the sand paper at least to start with because it greatly reduces the amount of required image processing, the coarse graticule from a printer gets you to within say 20um (though better really), at which point you bring in the sand paper sampled image to get you right down to the desired position accuracy you're after. This is what the close up images are actually looking at ..

A simple experiment with a monochrome webcam up close to a 0.5mm graticule steel ruler and a piece of P1200 sand paper alongside .. A circular piece of sand paper alongside a printed regular graticule scale (with a 0 degree index pattern as the starting reference) on paper or plastic film (on back of motor rotor disc) together with a simple high frame rate monochrome image sensor (maybe an optical mouse image sensor) on a raspberry PI board and tiny lens can serve as the position feedback sensor. A decent 600 real DPI laser printer can print a 100um period scale, a 2400 real DPI printer can print a 25um period graticule scale onto paper or plastic film. The PI board can do a little bit of image processing to count the passing graticules and also do a small amount of sub-pixel image processing to compute the position to way below sub-micron levels. The sand paper half of the image can be put through a very simple neural network to extract the exact position (absolute angular position) - after it has learnt the sand papers image signature at each graticule. edit: The attached image I scaled down, it's actually cleaner and sharper than shown (image pixel resolution from the webcam is around 10um from around 1cm away from the ruler/sand paper). Holding the camera steady enough whilst pressing the keyboard key to capture an image was a challenge.

150mm * 2mm steel disc (rotor part of the motor) with 3D printed magnet spacer and 2 layers of 24 magnets (48 in total) in place. The magnets we have here are only 2.9mm thick and only N35 strength, so used 2 layers. 5mm thick N52's on order to replace them when they arrive. Rotor so far ..