Member postings for Robert Atkinson 2

No the internet / WWW mostly runs on LINUX.
I've always said developer's should be given minimum specification machines. That way they won't write code that needs a fast machine and lots of storage to be usable

Needles inclusion of libraries and language "packs" annoys me. I once wrote some simple code for a pic microcontroller to develop the hardware. The task of writing "proper" code was given to the software team and after a week or two they came back asking for a chip with more memory. Turned out they were using a huge C coms library to send 3 characters down a serial line. This was "bit-banging" the I/O pins. I'd just sent bytes to the built-in USART.... My code went into the production units after all.

Robert G8RPI.

HI,

The hoist is complete, it just needs mounting and power si it has to be marked. If you look at any proper truck mounted crane you will see they are CE marked by the crane manufacturer. an analogy to your view would be that a flat screen TV did not need to be CE marked becaause it had to be mounted on a wall and plugged in.
Currently any item that falls under one of the CE directives has to be compliant and CE marked before it is "put into use" even if it is for personal use only. In practice this is not done and it is unlikely that any enforcement action, or even detection would take place for private individuals. What could catch you out is insurance. If you have to make a claim because of an accident or incident caused by a personally imported non-compliant item they could refuse to pay out. This could leave you homeless.

Robert G8RPI.

There are several similar "block and pulley" items on ebay like "mannesmann rope hoist" a random one is www.ebay.co.uk/itm/Mannesmann-Rope-Hoist-180-KG-Winch-Puller-20-Meter-VPA-GS-CE-TUV/202667237597
None of them seem to have the holding device of the Haltrac, maybe the patent is still in force. Not to difficult to add a cleat or rope stopper in a fixed installation.

Robert G8RPI.

I could not find that specific one but noted that none of the identical looking ones had no CE marking. This means that it is technically illegal to sell or use them. There is no assurance that they are designe or manufactured correctly. There is no indication that they are not OK, but I would not push the limits or get any part of my body under a load.

Robert G8RPI

There are a number of things that NEED old machines. A good example is programming older two-way radios. some of the programmers relied on the CPU clock speed to provide critical timing so not only do you need the right operating system and processor you need the right speed. Virtul machines don't help with that. Industries like Aerospace and nuclear which have long life span products and hde igh reliabilty can use very old machines in test systems because migrating to a new system would mean re-validating the software and hardware which can literally cost millions and take years. There is a small but healthy market for PDP-11 machines and clones for this type of application. Recently I had to find a copy of MS-DOS 6.22 to format a replacement HDD (actually a CF card) for a not that old Rhode & Schwarz radio test set. The original HDD was dead. The auto install program (which has to run from a PCMCIA card so that needed an older laptop) specifically looked for that version of format and FDISK and created non-stanard partions for the instrument software.

Robert G8RPI

If anyone near Cambridge (UK) wants a working, small Samsung laser printer I have one free if they want to come and pick it up. Send me a PRIVATE MESSAGE if interested. Don't reply here and no I won't post it.

Robert G8RPI.

Hi,

I'd suggest you don't do all of one side at a time. Take all of the surface plus a bit off one side, flip it over and take the same off the other side. If possible stress relieve and then take a second cut at the first side, flip and do a final cut.

Robert G8RPI.

Talking of pins, in a previous employment we made (I say made but two specialist subcontractors were used) pins that had flattened points less than 1um ) 0.001mm in diameter and split down the center like a quill pen. The run-out was <2 um (from memory) and they were supplied as sets with the lengths matched to much less than 1um. The material was tungsten carbide but even so just touching the point was enough to damage them. They were very expensive. Shown as item 21 in this patent that gives an idea of the application.

**LINK**

The pins weren't patented, to do that would have revealed how we made them.

Robert G8RPI

One problem with this type of show is safety and liability. With multiple teams and no recognised build standard it's bit of a nightmare to control. The "rules" on the later BBC show would not have allowed some of the robots on other later series as "high emergy rotors" were not allowed.
Always remember these shows are for entertainment, not to promote engineering or even a fair competition. I've been innvolved with a couple of shows and what went on screen was not always what really happened.

Robert G8RPI.

My plan for this is to take the motor and gearbox out of an old cordless drill. I've kept an old Bosch that the NiCad batteries died years ago fir just this purpose. Some need the case to hold parts together but this can be solved at various levels of neatness (hacking the handle off to machining a shiny new housing. It will run off a 12V supply with speed control modified to a rotary knob.

Robert G8RPI.

I'm going to reveal a hidden gem here:

Get one of the Low voltage AC/DC power supples intended for use in schools like this one

https://www.ebay.co.uk/itm/POWER-SUPPLY-EJ0032-IRWIN-L-V-Variable-AC-8A-DC-5A/254479418781

or 8A one

https://www.ebay.co.uk/itm/POWER-SUPPLY-EJ32-IRWIN-L-V-Variable-8-Amp-AC-DC-volts/124032526494?

Search Irwin power supply. The also made one with stitched positions fron 2 to 12V

Griffin & George also made them.

Some are over-priced eg https://www.ebay.co.uk/itm/Variable-Power-Supply-Griffin-and-George-ltd-London/202874378189?

Some are absolute bargains like this https://www.ebay.co.uk/itm/GRIFFIN-AND-GEORGE-GRIFFIN-LT-VARIABLE-POWER-SUPPLY-/113986088771?

(No I didn't get that one but have an identical one).
These are unregulated and are much more suited to to plating, and running small motors than modern solid state digital units.

Don't forget that if you want to have sulfuric acid stronger than 15% you need an Explosives and Poisons Precursors licence in the UK

https://www.gov.uk/government/publications/licensing-for-home-users-of-explosives-precursors/licensing-for-home-users-of-poisons-and-explosive-precursors

Robert G8RPI.

Edited By Robert Atkinson 2 on 15/01/2020 15:58:10

In reality you need to know 3 electical specifications for a 3 phase AC induction motor

1. Voltage to Frequency Ratio (V/Hz)
2. Maximum Frequency
3. Maximum current

For a typical UK 1.5 hp motor these could be:

8 V/Hz, 60Hz and 2.5A

This motor is suitable for direct connection directly to the UK mains (50Hz 230/400V) as 8x50 = 400V.
If used on a VFD with voltage boosting it will run 20% faster at 60Hz and 480V with same max current (torque) so will provide 1.8 hp
Running at reduced speed reduces the power linearly to zero. At zero Hz (DC) you can apply zero volts. Note that you still get torque at 0V but its resisting turning, not providing it. This is how dynaimic braking and DC injection works. Try spinning a disconnected motor by hand and then try with the connections shorte together.

Note that the same physical size motor provides more power at higher frequency. This is why aircraft use 400Hz AC supplies, 8 times the power for the same weight of motor. The V/Hz rule applies to transformers too.
Aircraft voltage is 115/200V so V/Hz for motors is 0.5. This means you can run an aircraft motor on 50Hz but you have to reduce the voltage to 25V so there is little point.

Robert G8RPI

No it's NOT.

The VOLTAGE is reduced when the FREQUENCY is BELOW the rated frequency of the motor.
The VFD instructions you are reding assumes the motor you are using has the same rated voltage as the VFD output. Some VFDs can increase the voltage as the frequency rises to maintain torque and increase power but this depends on the insulation of the motor being able to withstand the higher voltage. Motors with increased insulaton ae available for this purpose. Note that the motor will not run any hotter with higher voltage because the main heating effect is I squared R and the current and resistance of the windings has not changed (yes there are increased bearing, windage and AC losses like skin efect but these are insignificant for the levels we are talking about).

I'll say it again it is FREQUENCY (speed) and CURRENT (torque) that determine the motor power, the voltage rating just sets the current at one frequency.

Robert G8RPI.

It's a bit concerning that the "bed" did not sit flat on this bench after he welded the two U sections together.........

I've been travelling so have off-line.

Please READ ALL THE THREAD BEFORE POSTING.

I've already explained the situation on running a 400V motor (does not matter if it's star or delta just that it cannot be wired for lower voltage). Running it at 29Hz (with no voltage reduction, maximum VFD can give) Gves more torque at lower speed. Runnng at 50Hz (same voltage -maximum) gives less torque and higher speed. THE POWER IS THE SAME.
The voltage rating of a motor is only to get enough current to provide the required torque at full speed. Star-Delta starters provide lower inital current and thus torque by putting less than rated voltage (0.577 times) across each winding during starting. This can be done to reduce electrical loading so supply requirements can be less OR to reduce initial torque to prevent mechanical stress.

The VFDs with higher output voltage than input either use a simple two capacitor full wave voltage doubling rectifier. This is only suited to smaller units as it has poor power factor, but it's cheap. larger and better units use a boost switchmode regulator that can also provide power factor correction with a few extra components. While a true Cockroft-Walton voltage multiplier uses the same basic technique of multiple capacitors charged in parallel and discharged in series as the full wave doubler it is defined by many more capacitors and thus higher multiplication.

Robert G8RPI.

You can't tell f the bearings are fitting properly unless you get some blue on them. It sounds like the bearings were replaced but not fitted and adjusted properly. They maybe be fine but you can't be sure until you check them.

Robert G8RPI.

Well I don't have a degree but I am an engineer. I qualified as a licenced aircraft engineer nearly 40 years ago. This is one of the few engineering jobs that actually need formal licencing. More recently I became a Chartered Engineer (and a Fellow of the Royal Aeronautical Society). So I don't agree that a degree defines an engineer.
As mentioned the image of engineers on the media does not help. Even on those programs showing engineering tend to concentrate on hitting things with hammers and things going wrong. This is becuse the media is looking to be entertaining, but the judge is the producer / director. I've been behind the scenes and on some engineering programmes and what ended up on the screen bore little resemblance to what actually went wrong.

SWMBO has degrees and a doctorate but does not earn anywhere near as much as I do

I never said that k made sense just that it is the standard. That said there are actually grounds for using m as the thousanths multiplier that long predate SI and the Kelvin. The terms mil (1/1000" and milli have been used for centuries.

At least with k & K it is pretty obvious which is which. With m & M it may not be clear especially in electronics. A single design may use milliohms and Megohms, millihertz and Megahertz.

Robert G8RPI.

Biomass is NOT low carbon, The reports say the Drax power station is now carbon neutral because it runs on biomass. Unfortunatly the biomass is wood pellets at least some of which is produced in america. The CO2 emitted in harvesting the wood, drying it or transporting it (ships burnig dirty bunker oil) is not counted. And biomass produces more CO2 per Watt than gas.

Robert G8RPI.

JasonB beat me to it!