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Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Todays Mystery Objects?
07/09/2023 07:52:54

Hi Michael, I sent you a private reply.
The squibs look like a male to male pipe coupler with different threads on each end, no through hole and 4 electrical connection pins in the small end.

Robert.

Thread: Acetylene bottles in the home workshop
05/09/2023 20:06:43

+1 on making sure your insurance company knows and it does not affect your cover.
It's surprising in the UK how many activities you can carry out "in" your own home as a hobby that would require lots of paperwork if done in the course of business.

For acetylene, as long as you are not making it, filling cylinders, compressing it to more than 0.62 BAR Gauge or using it at more than 1.5 BAR Gauge (the pressures in a cylinder and a fittted regulator don't count) you are OK. See:
https://www.legislation.gov.uk/uksi/2014/1639/

This has practical guidance:
https://www.hse.gov.uk/pubns/indg327.pdf

Transporting it is another matter, again check insurance. HSE have an interesting video that includes the planned rapid dissassembly of a old Fiat van.
https://www.hse.gov.uk/fireandexplosion/acetylene-research.htm

Robert.

Thread: Pre-Paint Degreasing
04/09/2023 19:14:30

Brake cleaner or acetone

Robert.

Thread: Compressor question
04/09/2023 10:47:23

What Clive says, but you really only need to "Tee" the normally open depressurising (unloading) valve into the large pipe between compressor and tank. The pressure switch can be connected to the tank port with the small pipe that currently feeds the pneumatic unloaders but you will have to remove the existing pressure regulator in that line.

Robert.

Thread: Old bearings never die...
04/09/2023 10:37:37

Requirement seems a little obsessive to me. Certanly during the working life of the aircraft they would not have bothered about the make. That is why there are standard size designations. I've actually received "refurbished" certified aircraft bearings where the two races had different manufacturers (VC10 flap drive thrust bearings). It was queried with the supplier and they confirmed it was acceptable.

Robert.

Thread: 2 pole or 4 pole for Myford ML7R
01/09/2023 21:13:37

A steel gland that directy contacts the mesh (screen or armour) on the cable and is fastened through the metal box is the ideal solution. No other connection to the mesh / screen is required in this case. The matal case must of course be connected to mains earth. The inside of the box under the gland nutsmust be free of paint or similar finishes.
If you use a plastic gland on the box then leave the mesh and outer insulation intact up to within a few inches of the VFD. One good way to earth the screen in this case is to use a 15mm compression fitting for water pipe. Fold the mesh over the olive and clamp it with the nut. Iflike most, the olive has a sharp edge break it with a file so it doesn't cut the mesh. Mount the fitting on a angle bracket fastened ot the same metal plate / box wall as the VFD.
The plumbing fitting trick is not good for the outside of the box because it does not provide mechanical support for the cable.

Robert.

Thread: Scams
31/08/2023 15:40:02
Posted by Martin King 2 on 31/08/2023 11:38:04:
Szabina
Ok I'm buying On the other hand, I will make your payment via UPS EXPRESS delivery
Nearly always eastern European names offering the relevant courier to bring me cash and take the item away, sometimes offering a £20 extra to reserve the item.
Cannot quite work out their angle?
Obviously we decline their kind offer......
Cheers, Martin

Typically the payment method allows the money to be withdrawn after you have parted with the item. To add even more they sometimes send more funds for you to pay the courier. So you loose the item and the cash you paid the courier. Variations been going on for years even before the internet.

Robert.

Thread: The beginning of the end for Copper telecomms
31/08/2023 15:33:28

SOD,

Sorry if I was not clear. I was referring to internet connectionsa (VOIP) and cellphones having common failure modes, not POTS and VOIP / Cellular. I'm fully aware of how the POTS works. POTS is required by law to provide a universal service (waiting time not withstanding) and back-up power. Cellphone and IP services don't have these obligations.
There is a similar issue with GNSS (sat nav) there are now many systems that rely on position, navigation and time information from these services with no alternative. Yes there is more than one GNSS now but many older systems only receive GPS. Additionally a severe solar storm could knock out all GNSS, Starlink and a bunch of other systems.

Robert.

31/08/2023 09:18:46

Starlink is Low Earth Orbit (LEO) so the need for a low angle view to the south (UK) to "see" a geostationary satellite over the equator is not there. As long as you can see a reasonable amount of sky it should work.
I do worry that VOIP does not have the resilience of POTS (plain old telephone system) A lot of people do not have reliable cellular coverage (not just in the "sticks" either) and there are some common failure modes. Ths most obvious of these is loss of power. There is no legal requirement for mobile operators to provide backup power and a lot of the backup that does exist is only for 3 hours.
https://www.ofcom.org.uk/__data/assets/pdf_file/0028/247195/Battery-backups-telecom-networks-have.pdf

Robert.

Thread: 2 pole or 4 pole for Myford ML7R
28/08/2023 16:47:38

Hi Duncan,

In a properly set-up VFD system using the E-Stop input will stop the machine faster than the normal stop button.
Cutting the power to a VFD with the E-Stop is not recommended as the VFD stores significant energy in the "bridge" capacitor(s). The electronics won't even recognise that power is cut until the voltage on this drops. Thus the stopping time is much longer than even a non-VFD motor with a power cut E-Stop. This is made worse by using an oversized VFD or when the load is light.
So a dedicated E-stop input is the best solution.

Chris,

As they say it has a filter built in you probably don't need an external one.
In theory a full set of electromagnetic emissions measurements should be carried out to ensure compliance with regulations. In practice this is seldom done for one-off designs even by professionals. The cost, typically a few thousand pounds, has a lot to do with it.

Robert.

28/08/2023 13:32:23

A metallic case also reduces interference. You can use an ABS box but you should fit the VFD and any filters onto a metallic plate that is then installed in the ABS cox. All earths, includng cable screens / armour, should be connected as directly as possible to the plate.
With plastic box the best way to cround the screen is with a metallic clamp. You need 360 degree contact. Even an inch or two of tail reduces the effectiveness of the screen.
If your VFD does not explictly have an EMC filter you should fit one. it also needs to be mounted on the plate.

Ther are two disadvantages to putting the E-Stop in series with the normal stop input:
1/ The machine will not stop as quickly.
2/ if ther is a fault in the normal stop circuit the E-Stop won't work either.

Robert.

26/08/2023 15:14:10

I can't comment on the paramrters as I don't have the same model drive.
The mains earth coming into the enclosure should go to a earth stud on enclosure and a separate earth lead goes from the same stud to the earth termainal on the VFD.
If the enclosure does not have a built in stud. use a 4mm bolt. don't forget to remove any paint under it. Use one nut to secure the bolt through the enclosure wall and a second to secure the earth cables. Ideally use ring tags.

For the E-Stop, yes just use the NO contact.

Robert.

Thread: 24V rectifier for lighting.
25/08/2023 18:30:53

As I mentioned earlier, it also depends on the nature of the moving object. A facetted item like a hex bar or the jaws of a chuck can be frozen by much lower light levels if the pulse coincides with a reflection in the irection of the viewer. Yes even less likely but still a problem when it does happen.

Nealeb,

Yes you would think the phosphor would broaden the pulse of a white LED. However it's not the case. Some time ago I was looking at alternatives to short gap xeon strobe tubes for a new analytical instument. Out of dilgence rather than expectaion it would work, I tried some phosphor type white LEDs. I was shocked at how fast they were. The turn-off was much faster than even an electrically quenched xenon tube.

Note that a lot of LED lights specifically use pulsed outputs. The human eye responds to peak light levels so for the same power consumption a LED operated at a 50% duty cycle with twice the current will appear brighter than if operation on all the time.

Robert.

Thread: Assembly diagrams - how are they done?
25/08/2023 12:27:58

You thought twice before putting Rotring to film. It's not a click of the undo button to change once the ink is down.

Thread: Raspberry Pi Pico
24/08/2023 20:47:19

Here is an interesting comparison. A modern car contains around 100 million lines of software code. A passenger aircraft has about 15 million lines.
One of the reasons for this is that avioncs software with any safety implications is not allowed to have any unused / redunant code. No libaries full of unused functions. One of the standards that defines this is RTCA DO178.

Robert.

Thread: 2 pole or 4 pole for Myford ML7R
24/08/2023 20:07:25

Hi Chris.
You don't or should not need a NVR with a VFD. The VFD whould have a input for an E-Stop switch and a setting for the amount of active braking applied. This is much faster stopping than just cutting power on a standard motor. Just cutting the input to the VFD means it will take LONGER to stop due to the stored energy in the internal "bridge" capacitor(s).
There should also be a parameter to select if the VFD restarts on power-on. This should be set to NOT re-start on power on. The start and stop buttons need only be low voltage / current momentary switches.

You should have an isolator. If the power socket is eassily accesible then pulling the plug covers this. I like to put a IEC 60320 C13/14 "kettle lead" plug and socket on the enclosure so you can instantly see that it is unplugged.

Robert.

Edited By Robert Atkinson 2 on 24/08/2023 20:08:16

Thread: Eclipse E225 scriber
24/08/2023 19:56:03

Well I just bought one of the NOS E225s at £4.99. That's less than a replacment steel tip for the E220.

Thanks for the tip (pun intended)

Robert.

Thread: Electric motors
24/08/2023 17:31:14

The connectors on the chinese motor control are sometiems called "aviation" connectors. This vendor
www.ebay.co.uk/itm/283143222904?
says they are rated for 400V and 10A. They may not break down at that but there is no engineered means of earthing the metal body of the free connector. They do not have a "make first break last" protective earth contact. They don't have the creapage and clearance distances required to meet international safety standards for >50V use.

To make thing worse. They have used a MALE connector on the OUTPUT to the motor. This means there are exposed pins with high voltage on them when the motor is unplugged. This is a serious shock risk.

Robert.

24/08/2023 16:43:55
Posted by mgnbuk on 24/08/2023 15:34:06:

Is it the particular metal body connectors used on that Chinese drive that you are not happy about Robert ?

All the Indramat, Siemens & Fanuc servomotors that use cable mounted connectors (rather than connecting boxes) I installed used metal body connectors.

Nigel B

Yes.
The connectors on the servodrives you used are designed for the purpose like these:
https://lapplimited.lappgroup.com/products/online-catalogue/products/epic-industrial-connectors/circular-connectors/epic-power-ls1/epic-power-ls1-d6.html
Note the range here:
https://lapplimited.lappgroup.com/products/online-catalogue/epic-industrial-connectors.html
includes power and signal variants.

The connector on the chinese unit are a type designed for low voltage DC. They date back to at least the 60's. A common applictaion was micropones on CB radios and the like.

Robert.

Thread: 2 pole or 4 pole for Myford ML7R
24/08/2023 08:11:55

I'd leave the maximum frequency (speed) at 65Hz. This gives you a bit more operating speed range but is well within the limits of your 50/60 Hz motor. As an aside, often the best utility can be had from a motor/VFD set up by arranging for the motor to run at higher speed than it's name plate rating. This is why I recommended, and fitted on my own ML7, a 6 pole motor. On a VFD this motor can easilly run at 4 pole motor speeds. It has the same rotor, bearing and fan construction as the 4 pole. It prodces more torque at low speeds than a 4 pole. I also fitted a larger motor pulley to reduce stress on the belt.

The revolution for 50 Hz probably only affects the RPM indication or parameters set in RPM. It should be set to the value for your motor but does not affect actual operation of the motor.

Robert.

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