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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: Free Electricity
17/01/2019 07:42:19

There is such a thing as free electricity (in the UK). As long as you own an electric or plug-in hybrid car and your employer lets you charge it at work. HMRC changed the rues last year and it's no longer a taxable benefit.

Robert G8RPI.

Thread: Bending copper pipe
16/01/2019 13:02:41

One advantage of Cerrobend is that it expands slightly on freezing making a tighter packing. Lead shrinks. Water expands too, maybe too much.

Thread: Gold Plating
16/01/2019 12:38:31

Another thought came to me. Electroless nickel immersion gold plating (ENIG) has become popular on printed circuit boards for electronic assemblies. This two layer system will work on brass. If you have a PCB manufacturer near you it might be worth giving them a call.

Robert G8RPI.

16/01/2019 07:28:06

Well first you need an EPP licence for the potassium cyanide (despite this people still seem to be selling kits on ebay). Have you checked with professional plating services? it may not be as expensive as you think especially if you are not in a rush.
You don't have to polish the surface but it will "enhance" the finish. So polished, machine turned or consistent sand blasting is OK but if there are scratches or odd marks they will show up.

Robert G8RPI.

Thread: Aircraft General Discussion
15/01/2019 21:05:38
Posted by Mick Charity on 13/01/2019 13:15:07:

On the subject of Airlander 10, I don't get it. What is it other than a novelty? Can it ever be a commercial success?

Unfortunatly most modern British airships have not been a great sucess commercially, but the Airlander could be. It's a lifting body design that has many advantages.


The accident it suffered was not a forced landing or even a problem with the airship itself. A winch in the mooring tower failled after the mooring rope was attached. The aircrew thought it had detached and tried to fly away. The airship pivioted around the rope and nose dived into th ground. They now have a release for the mooring rope at the airship end.

Thread: 540 Motor as a generator
10/01/2019 21:53:36
Posted by Ed Dinning 1 on 10/01/2019 21:35:22:

These motors would be a pain to rewind for more volts out. The simplest way would be to use a simple op-amp circuit to boost the voltage driving you meter. This would also have the advantage of reducing the load on the motor (generator).

Ed

Can you explain this "simple op-amp crcuit" please? Perhaps you mean a boost mode switching regulator. A boost regulator will give you a constant output at higher voltage but there are limits to what it can do.

Cheap chinese version

https://www.ebay.co.uk/itm/MT3608-2A-DC-DC-Voltage-Step-Up-Regulator-Boost-Converter-Like-LM2577-XL6009/132860039749?

Robert G8RPI.

Thread: Gatwick Drone 'Attack'
09/01/2019 18:24:32
Posted by Vic on 09/01/2019 17:01:04:
Posted by Pete White on 09/01/2019 09:28:46:

I don't we are getting all the information here.................as usual .

Yes. I think it's been agreed now that the only drones at Gatwick were ones used by the Police?!

NO it's not. The police have specifically stated this was not the case and ther were several credible witnesses. Police only flew their drones after the airport was closed. The Air Navigation Order applies to them too.

09/01/2019 12:30:45
Posted by mechman48 on 09/01/2019 10:58:23:

Simple answer would be … whoever buys a drone has to register it with the CAA with it's serial #, model #, name & address of the owner. These drones are usually operable within a 1or 2 kilometres of the control system ( apart from industrial / film / TV production models ) so should one be 'captured' then the authorities only have to look within that radius to locate the owner …?. Just my two pence worth.

George.

1/ Why would a criminal register a drone? Limiting supply or sales would be difficult with a global market and even DIY kits **LINK**

2/ You don't need an operator. Drones can be pre-programmed and could be pre-placed on a roof days previously. GPS is not the only navigation option and you can't go jamming GPS at an airport anyway.

3/ If active "man in loop control" was needed then there are various methods that could be used for long distance control.

This is potentially a big problem and there are other variations that could make a drone more of a hazard but I'm not going to give potential wrongdoers any hints.

Robert.

Thread: Safety Valve Operation
05/01/2019 18:45:39

The boiler test code 2018 volume 2 section 13.1.5 says

"It is considered good practice that every time steam is raised in a
boiler that if possible the safety valve is tested by lifting the spigot
to allow steam to escape. This action reduces
sticking of balls etc."

so sounds like it's not mandatory but I think you would need a good reason not to use a testable valve. Maybe boiler inspector can comment.

Thread: Assistance asked from Optics Fundi's please
05/01/2019 13:38:47

Hi,

the graticule goes under the eypiece see page 31 of

http://www.science-info.net/docs/b-l/BL_Stereozoom.pdf (original sales info too)

More info:

https://www.pyseroptics.com/graticules/technical-guidance-notes/how-to-size-and-fit-an-eyepiece-reticle/

calibration info

https://www.microscopeworld.com/t-microscope_reticle_measuring.aspx

Microscope service manual including cleaning cn be downloade here

https://www.manualslib.com/download/926854/Leica-Stereozoom-7.html

Teardown pictures:

https://www.eevblog.com/forum/testgear/cambridge-instruments-(bausch-lomb)-stereo-zoom-7-teardown/

Lots of graticlues cheap on ebay, most from China.

HTH

They are a nice 'scope I have one and used them for work in the past.

Robert G8RPI

 

 

 

Edited By Robert Atkinson 2 on 05/01/2019 13:40:04

Edited By Robert Atkinson 2 on 05/01/2019 14:43:36

Thread: Gatwick Drone 'Attack'
04/01/2019 17:50:25
Posted by Mark Rand on 04/01/2019 16:05:56:

In the mean time, Coventry council have just announced that they are going to ban all drone and UAV flights over council owned public spaces except for limited pre-authorised commercial flights, with an additional charge for any photography that takes place.

 

I'm not actually certain that this decision would stand up if challenged in court.

In reality they don't need additional laws, it's virtually impossible to operate a UAV from a public place without breaching the exisiting law (Air Navigation Order). even if you waited until the area as clear before taking off you can't stop somene wandering into your landing area.

 

 

Edited By Robert Atkinson 2 on 04/01/2019 17:51:06

Edited By Robert Atkinson 2 on 04/01/2019 17:51:26

04/01/2019 12:32:03

There are lots of options available to a determined wrongdoer. You don't have to use off the shelf devices with known technology. I bought a high speed jet propelled UAV from Holland several years ago

**LINK**

This was pre-gps and could fly a pre-programmed route using internal sensors only. £1200 including the ground support and flight programming equipment.

I'm not going to go into other options on a public forum and suggest others don't either.

Robert G8RPI.

Thread: An electric motor actuated vice
02/01/2019 20:49:31
Posted by Michael Gilligan on 02/01/2019 20:36:08:
Posted by Robert Atkinson 2 on 02/01/2019 20:23:08:
... That is a different situation your system did not stall, it was slowed to a halt. The drive signal was stopped and the motor is still in sync. < etc. >

.

The situation I described [whatever you choose to call it] is the one that I believe would apply to the Vice.

MichaelG.

Not really, you don't know when to stop the motor on a vice, unless there is a sensor which has not been mentioned. In simple terms a stepper motor has good static holding force i.e it resists counter torque. but they are very bad at producing a constant torque output. I guess one option would be to put a spring between the motor and load but you still need a sensor to stop the motor drive. A microswitch activated by the spring movement would work. A DC motor and current limit circuit seems much easier.

Robert G8RPI.

02/01/2019 20:23:08
Posted by Michael Gilligan on 02/01/2019 20:08:01:
Posted by Robert Atkinson 2 on 02/01/2019 19:55:38:

Georgineer is correct. When a stepper being driven at speed is stalled it looses virtually all it's torque

.

Perhaps we have a problem with semantics

I know for a fact that I designed a vibration test fixture for part of a weapon system ... this had to be rotated to various angles of 'roll' whilst being vibrated at levels representative of missile flight.

We used a stepper motor and toothed-belt drive, and it behaved perfectly.

Rotate and hold [energised = locked]

... I can say no more.

MichaelG.

Edited By Michael Gilligan on 02/01/2019 20:10:00

That is a different situation your system did not stall, it was slowed to a halt. The drive signal was stopped and the motor is still in sync. In the stall situation the rotor is out of sync with the drive signal and magnetic field. Typically the rotor is stopped (or in Georgineer's case moving in the opposite direction) while the magnetic field continues to rotate at speed. To re-sync the field rotational speed must be reduced until the rotor (and load) can re-align and lock together. If you increase the drive speed on a stepper it will accelerate smoothly to a point and then suddenly stall. There are other factors such as the coil inductance and supply voltage (these lower the current available at speed) but primarilly it's loss of magnetic lock that is the issue.

Robert .

Thread: Model engineers - enlisted in war efforts?
02/01/2019 19:59:57

Probably the bigest hobby contribution to WWII was amateur radio. They contributed listening stations from home as well as using their "hobby" for war emplloyment either as radio operators, training, development or manufacturing.

Thread: An electric motor actuated vice
02/01/2019 19:55:38

Georgineer is correct. When a stepper being driven at speed is stalled it looses virtually all it's torque as the time for the poles to magnetically/mechanically realign is much longer than the time the pole is energised. if ther is an opposing force it has no chance. Before the stall it depends to a large extent on inertia to stay in sync. You have to ramp the speed up and down to get full performance and any resonaces in the system can cause issues. Some stepper systems have intertial dampers (elastomeric mounted balance weights) on their shafts to help with these issues.

Robert G8RPI.

Edited By Robert Atkinson 2 on 02/01/2019 20:10:33

02/01/2019 12:44:06

If the vice is powerful enough to cause injury then it needs safety precautions. Just because it was good enough in the past does not mean it's good enough now. Old lathes had no chuck guards or zerovolt releases, new ones do, even the new (and most refurbished) Myfords.
I'm not the HSE or CE police, but as a professional I feel it is important to make sure that anyone asking for advice on this sort of thing are aware of the safety implications. When doing it for someone else it rises to a whole new level. There are too many ambulance chasing lawyers and insurance companies trying to get out of claims or recover costs elsewhere to take chances. The 4X4 community have learnt this the hard way. Helping pull someone out of a snow bank or ditch is all well and good, but if they don't sign a disclaimer beforehand they, or more likely their insurers can come after you for damage actually or allegedly caused during the recovery. Just because Frankenhealy did it does not make it safe, legal or a good idea. Relying on slipping v belts to limit torque is definitely not a good idea.

Robert G8RPI.

02/01/2019 07:25:13

If you use a "normal" permanent magnet brushed DC motor this is very easy to do. The torque of the motor is directly proportional to the current so all you have to do is use a constant current supply. As long as the maximum current is less than the maximum continuous current rating of the motor it will sit stalled producing the set torque and automatically take up any slack. You would probably want a geared motor and a ballscrew would be better than a plain nut. Speed is directly proportional to voltage so this can easily be a separate control.

The biggest issue I can see is safety. This is essentially a horizontal press so would need a guard and possibly a two hand operating control. Neither of these are much use for a vice. As the law currently stands you have to be compliant with CE regulations, certainly if using for business or supplying (Inc. giving away) to another party. This means Machinery directive, EMC directive and possibly Low Voltage directive. Note CNC vices operate behind guards.

While your friend may be happy to take the risk, if there was an accident his insurance company may not take the same liberal view and come after you and your house or other assets.

Robert G8RPI.

Thread: USB memory sticks
31/12/2018 13:38:54

Sandisk from Tesco is a good price quality compromise. Ebay and the like is just too much chance of gettng a fake.

Robert G8RPI.

Thread: Simple and accurate home "switch"
31/12/2018 10:43:22
Posted by Nick Hulme on 31/12/2018 01:54:50:

I recommend

 

1. Enclosed.

2. Silver Contacts.

3. Ditch the "Shade Tree" engineering, it's not funny, clever or useful.

Why silver contacts? Silver is not suited to precision low current switching. It tarnishes for s start. It's not suited to any kind of reliable low level (below 100mA 10V) switching. Commercial index switches are available such as the the Omron D5A but they are not cheap.

I'm not an armchair or shade tree engineer, I'm a chartered engineer who has designed and built motion control systems with 1 micron resolution and 10 micron repeatability. This was confirmed using laser interferometry with nanometer scale resolution.

Robert G8RPI.

Edited By Robert Atkinson 2 on 31/12/2018 11:39:32

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