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Member postings for John Haine

Here is a list of all the postings John Haine has made in our forums. Click on a thread name to jump to the thread.

Thread: Garmin sat nav
28/07/2021 16:51:43
Posted by Ady1 on 28/07/2021 10:07:39:

Someone has finally pointed out that there is a big gorilla in the corner of the room

What happens to British ships when satellites don't work?

My answer would be a laser sextant for use at night

Point it at the star, self levelling bubble horizon, self contained clock, push a button, tell it which star you just read, get a position line in 10 seconds.

Edited By Ady1 on 28/07/2021 10:12:17

Just to add to my reply, inertial navigation systems are used already for marine navigation and give a continuous real-time estimate of position with no external reference. Semi-automatic sextants exist that can take a sight on a star, and you can get a reasonable fix from a single star sight if you have the right almanac data, it's bearing, and accurate time (which can come from a low cost atomic clock). Though GNSS signals can be jammed and spoofed there are countermeasures, and given there are 4 global systems in operation, put up by the USA, EU, Russia and China, it's unlikely that all 4 would be unavailable at the same time - and multi-standard receivers are common. I think marine navigation would find it inconvenient if GNSS disappeared but it could be survived. The loss of time synchronisation on land-based cellular networks and financial transaction systems would be much more of a worry I think.

And that BBC report is awful, confuses GPS positioning with satellite communications, confuses Loran-C that uses low HF bands with cellular phones that use uhf and microwave bands.

If you think it's just foreign states that jam GPS this makes interesting reading.

Edited By John Haine on 28/07/2021 16:59:24

28/07/2021 10:39:26

Download Camsextant from app store. Don't even need to know which star. Why would you need a laser? Ships took sights at night for centuries without one?

Thread: Tesla fluidics
27/07/2021 10:19:40

Aha! Prior art!

Thread: Stepper motors
27/07/2021 10:18:45

I use XLR 4-pin connectors for all but 3 of the 9 steppers I'm using in the workshop. The 3 are the XYZ axes of the Novamill, and those are connected by a big multi-way plug and socket originally specified by Denford. So far in 10+ years I haven't had any problems with them.

Thread: A motor or a weight for Wildings Small Tower Clock
26/07/2021 19:08:54

Or use a stepper motor to drive the axis through a spring coupling, step the motor with pulses from the pendulum derived by an opto interruptor. Put a bit of preload on the spring, the stepper keeps it wound.

26/07/2021 19:04:27

If you look on the Frodshams website they briefly describe the electric drive for Clock B. This has a motor driving a worm and wheel with the wheel on the axis of the hour hand. The weight of the motor exerts a torque on the arbor that drives the clock and there's a mercury tilt switch that detects when the motor has drooped a bit below the horizontal and drives the motor to lift it to just above.

Thread: Stepper motors
26/07/2021 16:55:18

Excellent, glad it's sorted.

26/07/2021 16:07:16

Just to be pedantic, the PNP signals are also open collector though common cathode (i.e. common cathode)!

Thread: Leveling machines
26/07/2021 11:04:15

The key is to avoid bed twist. Levels are just a convenient way to do that. As they are relative measuring devices using gravity as a reference then making the bed surfaces horizontal at each end is convenient but not essential. Equally the bed doesn't need to be horizontal. But ordinary spirit levels don't have the sensitivity of an engineer's level, if they did they would be very hard to use. May be good enough to get close then do turning tests to finally trim the bed adjustment, this has been covered on here many times.

Thread: Stepper motors
26/07/2021 10:08:46

Driver data sheet says that direction signal needs to be stable at least 5 microseconds before active pulse edge.

26/07/2021 09:26:41

Try changing the pulse signal to trailing edge active on the controller. It may be that if the edges on pulse and direction are coincident it can't make up its mind.

26/07/2021 09:10:16

I can't find the documentation for the controller Steve is using online but there is a connection diagram showing the interface to the stepper drivers with a +5V line, which implies that it's using standard 5V levels. Actually the original CMOS levels were 0 and 5V (or Vcc at any rate, usually 5V), it was TTL that had a 5V supply but the logic levels were a bit lower because of using bipolar transistors. Later CMOS reduced the supply to 3.6V to reduce power consumption and that led to the problem with the PC parallel port. However the controller Steve is using is a dedicated design not using a PC. Still worth checking the logic levels in the documentation though.

25/07/2021 16:56:08

No need to change voltage! 24v should be fine.

25/07/2021 09:35:40

Actually I'm using the 2M542 drivers which are very similar. I have 6 of them, 4 on the mill (XYZA) and 2 on lathe, and found they behave exactly as expected.

The odd behaviour of the motor that can't make up its mind may hold a clue. One cause of that may be that the pulse and direction signals going to its driver have the wrong timing. If the active edge of pulse changes state at the same time as the direction the driver may get confused about which direction it should go in. The controller should have the ability to change this as a configuration option, or the driver. Look in the manual for the position of the jumpers J1 and J3. Does the controller work in "pulse/direction" or "CW/CCW" modes?

24/07/2021 20:33:53

Have you checked the axes for friction?

Thread: Wall Chart
24/07/2021 15:10:28

What numbers do you want? It would be trivial to generate a spreadsheet.

Thread: Stepper motors
24/07/2021 13:57:10

No, the driver regulates the current irrespective of voltage. Are the currents you quote the ones given on the motors? If so they are the maximum not the recommended operating level. As as been suggested check the sense of the windings in series or parallel. I use the same drivers on my CNC mill at currents of around 1 amp for X and y and 2 amps for z iirc.

Thread: The beginnings of Mobile Telephony
23/07/2021 10:57:17

By the way, everyone I know these days just calls them "phones". Still a bit of a misnomer when making calls is quite rare compared with browsing, watching video and looking at social media.

23/07/2021 10:32:46

I used to have a splendid photo purporting to show Mr & Mrs L M Ericsson in their open horse-drawn carriage, stopped to make a phone call. The driver is atop a ladder propped against a telegraph pole, and Mrs Ericsson is using a field telephone connected by wires clipped to the overhead lines.

Thread: Digital CNC phase converter build
22/07/2021 09:20:19
Posted by Stuart Smith 5 on 21/07/2021 18:28:30:

.......

The only thing I would say is that if Robert goes down this route, the star point of his proposed delta/star transformer (ie the neutral for his 3 phase output) should be earthed separately and not connected to the existing supply neutral.

Stuart

I'm not sure this is correct. The "implied" neutral of the 3-phase from the converter is at an AC potential of 138V relative to the incoming neutral; but a 3-phase isolating transformer will have a "floating" neutral at it's star point which could be connected to the supply neutral, and for safety reasons this may be desirable.

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