D869 Posted May 19, 2015 Share Posted May 19, 2015 Penlan, As far as I know (and I haven't heard any better explanation from the rest of the group since...) the latest theory is when the loco wheels meet some dirt on the track, particularly with the older higher current motors, a small arc is formed at the rail, which generates sufficient RF to disrupt the signal of the servo's in the near vicinity, causing the servo's to travel their entire length and throwing the signal arms all over the place. One particularly memorable test involved running a servo off a completely different power supply, with no signal wire attached to anything, and still making the armature move by skidding a old Farish 08 vaguely close by. Best Regards, Chris, the estranged member of the MAG. I wouldn't want to suggest that every single servo on the layout has a problem - most are OK but there certainly seems to be one area of the layout that is very prone to servo glitching and has resisted our efforts to diagnose and fix it for a long time. We are fortunate in having access to better electrical test kit than most folks (and someone to work it) but these problems can be elusive and intermittent and have repeatedly demonstrated their ability to return when we think that we've traced and solved them. I still think that servos have a great many advantages over other forms of signal control, but the glitching issue has definitely caused us to question whether we should find an alternative. So far I've struggled to find anything that could do the job of driving the five wires underneath our home signal post with anything like the small footprint occupied by the current stack of SG90 servos. Regards, Andy Link to post Share on other sites More sharing options...
Penlan Posted May 20, 2015 Share Posted May 20, 2015 .... I still think that servos have a great many advantages over other forms of signal control, but the glitching issue has definitely caused us to question whether we should find an alternative. So far I've struggled to find anything that could do the job of driving the five wires underneath our home signal post with anything like the small footprint occupied by the current stack of SG90 servos. I agree with you about the footprint, and as I've experienced in a different hobby, it's very annoying when it's right, but it's not. I did try servo's, etc., but there were problems which seem to be similar to yours, I gave up, went back to Fulgerex, but as I'm 4mm scale and no bracket signals etc., there is a little bit more room to play with. But we don't live in a perfect world. I seem to have reached an age when every project I attempt seems to be two steps back, one step forward. Link to post Share on other sites More sharing options...
RMweb Premium Izzy Posted May 20, 2015 RMweb Premium Share Posted May 20, 2015 The need for a small footprint was why I originally tried servos, being 2mm scale, and then converted them to stall design. I just removed the circuit boards and powered them off simple DC - I use centre-biased DPDT's. To limit the movement I use gear jamming combined with steel sprung wire acutators to absorb any excess travel, but others just used stop blocks on the arms. However you need the servos very firmly fixed for the latter. With SG90's about 1.5v is enough to power them - so you can run them off single alkaline AA/AAA cells if you need. Re-chargeables output 1.2v and this isn't quite enough to power them reliably, SG90's having a fairly large 10x12 flat can motor and about 320-1 gear reduction. As SG90's often sound like cement mixers - crude and rough - I changed to using EnErG 7.5d digital servos. These have small 6x12 coreless can motors and 615-1 reduction, they run nicely off just 1.2v. and sound sweet. You musn't use more than about 3v with any servo as a stall design. The power they generate will wreck the gear train and/or rip the servo out of a housing - guess how I know.... Izzy Link to post Share on other sites More sharing options...
Hroth Posted May 20, 2015 Share Posted May 20, 2015 Is he the "Robbo" Ormistan-Chant of our times? Ian D'you remember the occasions when R O-C used to sign his missives "ex GWR" to add weight to his opinions? Link to post Share on other sites More sharing options...
Horsetan Posted May 20, 2015 Share Posted May 20, 2015 D'you remember the occasions when R O-C used to sign his missives "ex GWR" to add weight to his opinions? Were they written in green ink? Link to post Share on other sites More sharing options...
Adrian Posted May 20, 2015 Share Posted May 20, 2015 probably copperplate! Link to post Share on other sites More sharing options...
Hroth Posted May 20, 2015 Share Posted May 20, 2015 Were they written in green ink? Possibly. Having seen Portillos jaunt in Birmingham on BBC4 yesterday, probably using a genuine GWR branded steel nib too! Link to post Share on other sites More sharing options...
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