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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: 24v dc motor powering a drill press
22/03/2019 17:28:23

OK,

This is probably "specmanship" the 3A , 11A or whatener i probly the no load or minimum load current and is given so you can "calculate" a long battery life. I'll bet anyone it closer to 100A when pulling a 180 person uphill.

Robert G8RPI.

22/03/2019 15:22:02

Sorry, but there is no dot. The other dots and colons are square and clearly visible.
There are 3 leads on this motor the low current one you mentioned earlier is not the power connection, it's probably a temperature sensor.
This motor is much too big for 265W, it will be 950W output and 2650W electrical input. Peak efficency for a PMDC is adout 65% but that is at 10% load. at rated load it's likel to be 45%. This is a 4 brush motor which are less efficentso the 36% indicated by the data plate for max load is entirely reasonable. We hae no idea what the duty cycle is.

Robert G8RPI.

22/03/2019 07:38:09

It's a 4 brush motor with a flat braided strap for connection, despite the spacing on the nameplate, that alone says it's 110A current rating not 11A. You can get speed controllers designed for robots that will handle this sort of current. Search for high current pwm motor speed control e.g. **LINK** (from search no idea if it's any good).
Unless doing sustained drilling a couple of 12V lead acid batteries and a intelligent charger would be easier than a 100A power supply.
Brushed DC motors do not loose torque with reduced speed. Torque is only limited by the available supply current and voltage, current rating of motor / supply and mechanical strength. Normally the winding resistance will limit the current and thus torque, but if you increase the voltage to compensate the torque will go up. A controller with speed feedback will do this automatically. Obviously the available mechanical power goes down if you reduce the speed at the same torque, this is the laws of physics.

Robert G8RPI.

Thread: Inverter Tripping RCD
21/03/2019 12:34:38

This is an old thread, but it contains a worrying comment from john swift 1

"they provide a practical solution in the form of a switch to disconnect the earth connection from the EMC filter"

You should NEVER, EVER REMOVE THE EARTH from an mains EMC filter for any reason. Doing so will leave the body of the filter (and possibly the entire equipment) "live" and an electric shock hazard.

The manual John linked to describes removing or disconnecting the filter completely (not a good idea as the drive will cause interference and is therefore illegal). However in that manufactures smaller drives this is done by pulling a tab that disconnects the filter.

As suggested by Gary an isolating transformer should prevent the tripping, but it brings it's own issues. The drives are industrial components and should really be installed in a circuit with correctly sized protection. Unfortunately most domestic "part P" electricians (and at least 1 supposed industrial one I've met) don't understand the requirements.

Robert G8RPI

Thread: ML7-R tumbler gears
19/03/2019 07:24:45
Posted by Hopper on 19/03/2019 03:32:25:

<SNIP>.

Plus, if the Tufnol gear were for a "weak link" effect, they would have only fitted one and not two, you would think.

Edited By Hopper on 19/03/2019 03:33:31

Not for production, that would be two part numbers for otherwise identical parts to make, stock and keep track of. That is extra cost. And the SRBF gear is probably cheaper anyway. But like so many of these things only the original designer knows the real reason. I've certainly designed things where you would not be able to guess why I chose a part.

Robert G8RPI

18/03/2019 22:48:42

The broken gears do seem to be made from rod or tube rolled material rather than sheet so will have weaker teeth.

A couple of people have rubbished "Tufnol" however Tufnol is the manufacturer not the product. They make a wide range of materials, but we are talking about laminated phenolic resin materials. Within this product there are paper and fabric types. What most people call Tufnol is the fabric material. Even then there are different grades. The classic ones are Carp, Vole, Whale and Crow. Carp is the premium fine weave material. It has excellent properties and is frquently used in aerospace, both on aircraft and even more for jigs and fixtures.
Don't compare cheap imported material with a premium British product.

Robert G8RPI.

Edited By Robert Atkinson 2 on 18/03/2019 22:49:40

Thread: Tool Post Milling/Drilling Attachment
18/03/2019 07:36:24
Posted by Ian S C on 17/03/2019 08:32:17:

Most tread mill motors are PM DC motors, they also make quite good alternators.

Ian S C

A PM DC motor will never make an alternator of any kind. The commutator rectifies the rotor output so they produce DC. They don't even make good generators as you cannot control the output voltage for speed or load variations. I guess you could use a 230V one with a switchmode step down voltage regulator but its a bit of a weird approach.

Robert G8RPI.

Thread: Workshop insurance
17/03/2019 21:59:12

+1 for NFU Mutual. I have always found them very good for odd stuff like modified landrovers and gas turbine (jet) engines. They seem to be pretty pragmatic about things.

Thread: Why do both power hacksaws and bandsaws exist?
17/03/2019 09:05:27

Big professional ones still exist too

www.zoro.co.uk/shop/power-tools/power-hacksaws/ajph200-hydraulic-hacksaw-machine-400v-3ph/p/ZT1028546X?

Lot of money £6000-£18000 for a saw though!

Robert G8RPI.

Thread: Tool Post Milling/Drilling Attachment
16/03/2019 22:53:26
Posted by Roderick Jenkins on 14/03/2019 23:01:52:

Good question. This looks like the speed controller **LINK** It seems to run equally well in either direction by swapping the motor leads.

As it reverses by swapping the supply it is 99% certainly a permanent magnet DC motor. It looks like a PM. The odd 1% are the same as a "universal" (AC/DC) motor that has a full wave rectifier connected to either the field OR the armature winding. I've seen this on a couple of motors, it allows you to have a remote reverse switch with only two wires to the motor. It can be retrofitted to a standard universal motor. As you probably kinow to reverse a universal you have to swap just the field or armature.

Robert G8RPI.

Edited By Robert Atkinson 2 on 16/03/2019 22:54:31

Thread: Mixing Gear Module?
14/03/2019 07:26:38

The obvious answer to me is to ditch the gearbox and direct drive the leadscrew with a servo motor (or stepper) with a controller that is driven by pulses picked up from the headstock spindle (reluctance sensor off existing gear teeth or a new opto.). Any decent controller will be able to electronically gear the servo to the head at whatever ratio you need.

Then again I'm an electronics engineer.

Robert G8RPI.

Thread: LED lighting
08/03/2019 07:37:52

Hi,

If there are 24 LEDs in the light then there must be 2 series strings of 12 wired in parallel. 1.7V (40/24) is not enough to light a white LED. For 10W wee need 0.25A at 40V So for resistor value (if we work on the peak voltage for a safety margin) the resistor needs to drop 320V - 40V at 0.25A so Ohms law gives us 320-40/0.25 = 1120 Ohms.
So say a 1000 ohm resistor. However the power rating of this resistor is 78 Watts (280x280 /1000) so it is not a practical solution unless you want a heater as well.

Robert G8RPI.

Thread: Hydraulic test set up
03/03/2019 21:53:11

Two valves in series in liquid pipework have a potential issue that if you leave them both closed with fluid in the system thermal expansion can cause severe damage. The gauge will allow some expansion but if the pipe volume between valves is much larger than the volume of the bourdon tube in the gauge even normal UK daytime temperature changes could damage the gauge. One valve between pump and gauge will do all you need.

Robert G8RPI

Edited By Robert Atkinson 2 on 03/03/2019 21:54:30

Thread: Huge dial gauge
01/03/2019 13:01:27

Most likely for a measurement indication point that was relatively distant from the adjustment / setting location position. Now we would just use a electronic sensor with a remote display.

Thread: Filling defects in slideways
21/02/2019 21:26:23

+ 1 for Devcon repair putty. As Clive said, drilling shallow damage is a good idea. I've seen a magnetic base drill with large cutter used on a big machine to turn spot damage into round or chain drilled depressions with sharp transitions from base metal to filler.

Robert.

Thread: Model trains stolen - Kent
17/02/2019 18:17:25

Last thing you want is a published article on where to put a tracker, it will tell the theves where to look. Power for a tracker is a problem. Those in cars have internl batteriws kept charged from the main battery. Most steam models do not have a battery and generator. A hiding place where th antennas still operate is difficult on a metallic model. One thing every one should do is to to make a mark or number in a non-obvious place known only to you so the model can be identified if recovered. Don't forget to take photos of the marking.

Thread: What is this electric clock mechanism
07/02/2019 12:25:32

This is not a "IBM/Simplex Synchronous Correction cycle" clock as suggested by SOD, it's a minute impulse with sync. Normally 1 ppm on red back pair but if out of sync a (normally manually initiated) series of rapid pulses on the white / black fast forwards until the cam switch opens. A capacitor discharge as suggested by Bazyle is a good idea. charged to between 12 and 24 V by a series resistor and discharged by a transistor through the coil.

Note that the IBM system is different in detail to the British ones.

I could be persuaded to do a circuit for you if you wanted. For a little extra I could put an rubidium standard in it so you would have your own atomic clock with 1 minute resolution

Robert G8RPI

07/02/2019 07:38:12

Please don't destroy this artefact by putting a normal movement in it. They are fairly simple to drive and if you don't want to DIY, have a look at this

**LINK**

Off the shelf module available, but low cost is relative. For DIY you could hide a quartz clock with a disk with holes in place of a hand and a slotted optocoupler detecting the holes and driving the coil. just adjust the holes for the pulse rate needed. (for mains use a synchronous motor and gearbox with a microswitch or if you are that way inclined a PIC Arduino or RPi

Robert G8RPI

Thread: Testing for isolation
03/02/2019 21:12:55

Flash-over can be deadly.
I know of one case when a technician was working on some "low voltage" (240V) instrumentation in a cabinet with a 44kV underground cable termination in it. The instrumentation was blowing a small sand-filled ceramic fuse. The technician ran out of fuses and replaced it with fuse wire. The fuse wire blew and the plasma created in the cabinet caused the 44kV feed to short out. The cabinet exploded and the technician was killed.

Thread: Mystery optical device
02/02/2019 22:15:50

Most DLPs use a simple rotating filter wheel but some of the early high end ones use a combiner similar to the splitter shown but it's easier to combine colour than split them so simple methods are used. The spliter uses "dichroics" that reflect one set of wavelengths and transmit another.

Similar devices are used in fluorescence microscopes. I designed equipment using this stuff for several years but have now gone back to aviation .

Neil may be interested to know that I used to use Starlight Xpress cooled CCD cameras in instruments. They were sooo much cheaper than "proper" scientific ones that used the same, normally Sony HAD, CCDS. This come back to topic because these CCD are monochrome and intended to be used 3 at a time for high end video cameras that use dichoric splitters like the one pictured (but smaller). Being for a small market CCD availability was sporadic.

Robert G8RPI.

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