Possible tach reader problem??

Scott,  Just to be clear it is the front truck without tach that is always the one the stops.  At one point you say front truck, buy later rear truck.

It definitely sounds like when the engine is pulled faster then it thinks it should be going the front truck stops as the circuit tries to reduce speed.

I would make sure the front motor has no binding.  I also would test the engine in a cradle to see if both trucks start at the same voltage.  Make sure wires to front engine are ok, 5 pin plug all the way in.

This may be a motor/truck issue more then a tach issue.  Are you sure this engine is as fast as the other two.  Seems that it is a little slower and when it is pulled, thinks it is going too fast and reduces power to the motor.  At that point the front truck stops despite both trucks getting the same power.  Make sure nothing binding the motor or gears (hair, carpet fiber, etc...)  G

G

 I see the error in my description and will edit, but yes it always the front truck(the one without the tach reader) that is stopping.

 I rechecked all the plugs and harnesses again, but I'm not seeing anything that loose, bare, shorted, unplugged etc.

 Running upside down in a cradle both trucks appear to be moving at the same speed, although the truck with the tach reader seems to lead the other truck by a tad on start up. They appear to slow down in sync and obviously both stop at the same time when power is removed. 

 Like I said I ran all 4 engines uncoupled around the track in a lash-upand they maintain perfect distance from each other in forward or reverse. The problem starts when I couple them up.

 I have had tach readers go bad before, but usually they exhibit very erratic operation when running alone or lashed up. This does not do that.

 Scott

While running the engine apply your finger as a brake to each truck one at a time.  See how they respond.  After shutting down, unplug the motor plug and measure the resistance of both motors.  My guess is that the front truck motor may be going bad.

Tach seems to work, and since the rear motor responds properly, but the front wants to stop quicker, I think it must be the motor or more friction in the front truck drive gear.

The opamp that does the speed control is on the power supply.  You could swap in a different power supply and try it.  But I still think both motors would stop since they are NOT independently controlled.

 Finally had some time today to work on this problem. I looked over everything once again and still could not find anything wrong. I ran the 3v engine by itself over the course of about a hour. While running it I changed directions and speed about every ten mins or so. After running the 3volt engine by itself I once again lashed it up with the other three U50's and the truck problem did not re-appear. Not sure what happened, but it appears that the truck problem has gone away.

 Now I have another question about DCS signal strength. I noticed that when running the 3 volt engine by itself I can check track signal while running or stationary and I get consistent 10's or a occasional 9. Once I add the 3rd or 4th engine my track signal results are a crap shoot. If I try to read with a 3 or 4 engine lash-up while it is running it gets no higher than 3 and usually stays around the 1 or 2 area. If I check the signal strength with the lash-up stopped it wonders all over the place.........low as 3 and high as 10. Leaving all four engines on the track, with it powered up, and I take each engine up to the active list, the 5v engines all read 10 and the 3v is no higher than 3.

 I checked all my drops for loose connections and everything looks OK. With all four engines lashed up and running, track voltage maintains about 18v, and current stays around the 6amp range(smoke units turned off).

 Any ideas on this problem?

Scott

Interesting....I don't think I ever thought about checking the track signal with an MU.

Does pose an interesting question.

But I'd bet a dollar that Barry knows the answer, wait for him to chime in. 

Wonder if anyone else checks signal w/ an MU?

Greg

Scott & Greg,

Running multiple engines at the same time while performing a DCS signal test is going to yield lower, and perhaps inconsistent, readings as opposed to having only the test engine running.

The DCS signal is "measured" by the number of data packets sent (100) vs. how many are acknowledged by the engine, and the acknowledgements received back by the remote. With more engines on the track, some packets are simply getting lost in the increased noise of the other engines.

One might expect that normal operation would be adversely affected when running multiple engines. However, in normasl operation, as oppopsed to during DCS signal testing, packets are resent and lost packets won't necessarily maniefst themselves as errors.

On the other hand, DCS signal testing, by it's very nature, is a much more exacting process. Multiple engines, as well as test engine movement, can and typically will cause lower signal readings. That's why the most accurate DCS signal testing is performed when no other engines are powered up and when the test engine is stationary.

To check the signal strength around any sized layout with the locomotive stationary would take a looooong time, no?  You have to terminate the test, move the locomotive, then start the test again.

John,

To check the signal strength around any sized layout with the locomotive stationary would take a looooong time, no?  You have to terminate the test, move the locomotive, then start the test again.

For the most accurate reading, yes, that's absolutely correct. However, unless troubleshooting a specific problem, generally an engine moving at 5-10 SMPH will yield usable results.

When recommending a DCS signal test during problem resolution, as is generally the case on Forum threads, I will always specify a stationary test with no other engines powered up. This is intended to pinpoint specific issues with the greatest accuracy.

Thanks Barry.  I'm trying to get DCS sorted out on our club layout, and there's too much track to stop every time.   My plan is to run the track cleaner for a few laps and then run around and do the testing.

Guys thanks for the feedback.

 The reason I brought up the signal strength question, is that when trying to build a lash-up with the U50's, once I add the 3rd or 4th engine the 3v engine will come up and say "Engine Not On Track" and I wondered if this has something to do with the 3v engine having such a low signal strength while the others are at 10's.

 I don't know if this is just coincidence or not, but I just lashed up six 5v GP9's without any problems at all, then added a 3v geep and it could not find that engine either. Once I removed the other engines, it picks it up with no problem at all, but with more than 3 or 4 other engines on the track at the same time, No Dice!

BTW I am using revH TIU's. Would a revL TIU solve or help this problem?

 Scott

Again I finally had some time to look into things further. Found out that my signal strength problem was in the TIU. Switched to a spare revH TIU and I'm hittin perfect 10's, with as many a 6 engines lashed together, running or stopped. Also the issues I had with not finding the 3v engines has now gone also.

 Now the bad part is my truck problem has reappeared very consistently; and on more than just the U50.

I spent quite a bit of time trying various combinations of lash-ups using 5v & 3v ps2 diesel engines. I'm now getting this to show consistently with almost any 3v&5v combination. It seems that upon starting to move the 5v engine always leads the 3v by a split sec, which will cause it to "push" the 3v engine and the truck without the tach reader will stop turning. Once you  ramp up to about 5-6mph it will usually start turning again, but not always. It seems the heavier the engine the more sensitive it is.

Any combination of all 3v or all 5v and I cant duplicate the problem, but mix them together and it's a issue.

 Now that I look back I remember having this problem last year when I got a GN SW-1 and tried to run it with three GN SD-24's. If I have the SW-1 at the end of the lash-up and running the lash-up forward everything works great. As soon as I reverse direction the SW-1 will drag one truck till about 5-7 mph then its starts running again.

 BTW I have all my acceleration and deceleration rates set the same in all the engines.

It gets frustrating if I want to lash-up a combination of engines with different voltage boards. If your not closely watching you'll end up having a 3v engine dragging a truck.

 Scott