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161st message | this message only posted: 13 Sep 2018 11:40
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from:
Nigel Brown
 

 

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Andrew Duncan wrote: madscientist wrote: having reviewed both , I found the switching in cobalts to be more robust then tortoisesHello Dave
That’s interesting, have you understood why? Like Martin I’ve had a Tortoise apart and although by looking I wouldn’t condemn them out of hand, my experience says there is something wrong with the design both from my experience and those of others. 

Have you taken one of the Cobalts apart to see why they seem better?

Kind regards 
Andrew
For the record, apart from the fact that I find them noisy, I've not had any problem with the switching on my tortoises. I do take trouble to make sure that when the tortoise is in mid travel the switch blades are also in mid position.

Nigel

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162nd message | this message only posted: 13 Sep 2018 12:47
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Please do not send requests for help direct to me via email or PM.

Post your questions on the forum where everyone can see them and add helpful replies.
There are 3 problems with the Tortoise switching:

1. plain copper is not a satisfactory contact material for other than very low currents. The Tortoise switches use phosphor-bronze wipers running along tracks of thin copper foil on the printed circuit board.

If you can guarantee that you will never switch into a short-circuit condition, they are probably acceptable. That would happen for example if a loco or just a metal wheel is left bridging an isolation gap in the rails, with power on, and the points are then reversed against it.

What then happens is that the full short-circuit current passes through the copper track as the wiper makes contact with it (until the short-circuit protection operates). The thin copper is very likely to be burnt and permanently damaged. Future operation of the contacts will be degraded, probably leading to a high-resistance contact instead of zero.


2. the actual design of the printed circuit board is very poor, with the tracks misaligned with the wipers. Andrew Jukes went so far as to have new circuit boards made for his Tortoise point motors.

A full account of all this is at (2 pages): 

 https://www.scalefour.org/forum/viewtopic.php?f=5&t=360

I believe the Tortoise circuit boards have since been through several design revisions by the manufacturers. That is indicative of the problem, and it is not easy to know if you are buying fresh stock.


3. contact pressure relies on the Tortoise motors being used in stall mode, i.e. the current remains on permanently in each position. As simple point motors they will operate the points just fine if you choose instead to switch the power off after movement is complete. This saves on power consumption and eliminates the slight buzzing noise from the stalled motors.

However, if you do that, the back pressure from the points linkage causes the plastic drive arm to twist slightly, lifting the wipers from the copper tracks.

Some have argued that this is not a fair criticism, because the Tortoise motors are intended to be used in stall mode, as indicated in their instructions.

I would argue that it is indicative of the poor design of these switches, and limits a useful way of using the Tortoise point motors.

One user I know, to operate his Tortoise motors, would connect the required one to the loco controller (DC) with a simple on-off switch, drive the points across visually using the loco controller, and then switch it off. It worked fine as a simple method of operating the points, needing no extra power supply or double-pole switches -- but failed because of the failure of the internal polarity switches to maintain contact with the power off.

Martin.

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163rd message | this message only posted: 14 Sep 2018 07:45
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from:
madscientist
 

 

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Andrew , Martin has covered most of the issues

I disassembled a recent tortoise and a cobalt omega ( I also traced the circuit diagram out for the cobalt )

As Martin says , tortoise is using bare copper , cobalt is gold tinned , the cobalt  wiper is better engineered and the contact area is better

As cobalts don’t use a special stall motor , merely a 5V motor that is powered via a comparatively high resistance feed , they then use a considerable gear train to reduce the motor speed to the arm speed , much more then the tortoise . This means that it’s not possible to mechanically force the actuator arm back from its stop position , so cobalts remain in position with the power present ( in stall ) or not , whereas with tortoises you can move the arm and hence if you remove power you loose pressure on the blades

The main thing I don’t like about the cobalts is their power consumption in stall , upwards of 60mA stall current when the operating voltage is 12v , around 30mA when actually moving ( if you can arrange it , try and power cobalts from about 7v , anything above that is wasted in the internal zenner diodes ) . There is no audible buzz from the cobalts in powered stall 

Note these comments apply to the cobalt omega , not the IP

And of course the cobalt is considerably smaller and has a lifetime warranty 
As a general comment , I do feel the switches are a weak design in both tortoise and cobalts and a belt and braces approach would be to use the point motor switch to switch an external relay,  it I doubt many will bother 

All in all , I can’t see why anyone would bother on this side of the pond with tortoises quite frankly

Dave

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164th message | this message only posted: 14 Sep 2018 13:18
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from:
Andrew Duncan
Reigate, United Kingdom



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Hello Dave
Very clear succinct answer thank you. The only bit I didn’t understand was the reference to the two different types of Cobalt. Are you referring to the ordinary and DDC ready types?

Thanks again 
Andrew

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165th message | this message only posted: 15 Sep 2018 00:00
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from:
madscientist
 

 

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Andrew Duncan wrote: Hello Dave
Very clear succinct answer thank you. The only bit I didn’t understand was the reference to the two different types of Cobalt. Are you referring to the ordinary and DDC ready types?

Thanks again 
Andrew
DCC concepts tend to love their own marketing speak  , so you gets lots of it ! 
The Omega , is now the lowest spec , which is an improved version of the original ( the classic ) 

The Analog IP is basically a V2.0 version of the omega , with improved power supply range ,microprocessor control of the motor , and improved contacts , it’s easily worth the extra 2 quid or so, in fact I wonder why DCC concepts keep the omega in the range .( the difference is nearly nothing if you buy the 6 pack )  It also cuts off the motor at the end of the movement removing one of the big issues with the Omega , which is the high stall current , so unlike the Omega , the IP isn’t actually a stall type PM at all. 

The analog IP isn’t really any more “ digital ready “then the omega other then it can use DCC track power as a source of motor power 

The digital IP is DCC compatible 

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166th message | this message only posted: 15 Sep 2018 09:55
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from:
Andrew Duncan
Reigate, United Kingdom



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Martin Wynne wrote: madscientist wrote: As Henry Ford said 

If I asked my customers , they’d have just said “faster horses”
Which don't need petrol, and don't drive on the wrong side of the road if they lose the GPS signal. :)

Andrew is modelling the railway at a time when they employed thousands of horses, see:

 http://www.movietone.com/assets/BMN0624/wmv/BMN_92091_3.wmv

Here is an interesting picture, from the above Movietone newsreel clip showing (allegedly?) the last working shunting horse on BR, filmed on 27th Feb 1967. Notice the catch points in the foreground -- the turnout rail is chaired on alternate timbers only. The only reason I can think for this is economy of chair castings. This may be a one-off for this location (Newmarket) or maybe typical of GER / LNER practice generally -- anyone know?



Picture linked from the PhotoBucket site: http://s193.photobucket.com/albums/z205/lamdelz/

regards,

Martin.
Martin and Dave

Now I’ve just caught up with you on this. When Dave first made the rather bold statement that you were getting not only older, but odder too boot, I was expecting verbal  fisty cuffs or pistols at dawn,
For some reason the meaning of Henry Ford quote eluded me. It took my French wife ( and it’s a well known fact that the French have no sense of humour) to explain to me what Dave was saying! Which made us both chuckle, me at both myself for not understanding it in the first place and at Dave’s wit. 

Your response brought further amusement at the kitchen table this morning. Thus disproving my previous statement about the French;a very entertaining way start a Saturday morning. Thanks to you both. 

Andew



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