Problems with pickup?

[AussieAlex90]

Hi all, 

I have a Hornby tender driven flying scotsman that has been converted to DCC. I have an odd problem that for the life of me I can not work out what is happening. I have multiple diamond crossings on my layout and the engine will stall when going over these (they are the plastic frog type) HOWEVER it only happens if the loco is going forwards, if the loco is going in reverese its completely fine even at the slowest pace it will go. 

My other engines (the Railroad version of the flying scotsman and a little 0-6-0T) run fine and have no problems, the track and the wheels are freshly cleaned and has new traction tyres installed. 

I can only imagine it must be something to do with decoder? I am having another issue with the engine where it seems the top speed has been limited, the engine will only speed up until the throttle gets to the half way point, then it "maxes" out and the other half of the throttle appears to do nothing. This happens in both forwards and reverse.  

I will include that at this stage I have no way of resetting the decoder (I have the Hornby select controller) Is there anything else I can try?

Thanks. 

[jane1707819582]

where the loco connects to the tender is a post and spring loaded drawbar ,give this area a good clean ,

i dont think you have a problem with the decoder other than it is losing it's connection to the track,

with the select you have very few options to alter any cv settings 

[Chrissaf]

....where the loco connects to the tender is a post and spring loaded drawbar ,give this area a good clean.........EDIT: and/or adjustment.

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Just to expand upon what Jane is suggesting. In reverse, this electrical connection post between loco and tender will be in compression. Whereas in forward direction it will be in tension. Since forward is likely to be used more often, the rubbing and wear on the electrical contact area will be more. When in reverse, the geometry of the contacts is likely to change slightly so that the 'in reverse' the electrical contact area is a fresh little used area of the contacts.........just a possible theory.

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I believe on this model, the screw bolt fixing that holds the rear pony truck to the chassis, may possibly pass electrical pickup current to the motor in the tender. So this should be taken apart, cleaned and re-assembled too.

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Both of the comments above assume that jane is correct that there is a post type electrical contact between loco and tender. I assume Jane is correct, as I am not familiar with this model in any detail.

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I concur with Jane.....very unlikely to be related to anything to do with the decoder itself. Other than it is loosing sight of the DCC signal due to a physical electrical continuity issue.

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With regard the speed control issue......what brand / model of decoder?

[AussieAlex90]

Hi Chrissaf, 

The decoder is the hornby one, I am using the select controller. Although I do have the elink and Railmaster on the way. 

After some more testing, I have now worked out that the tender pickup wheels are spaced so that they exaclty line up with the plastic frogs on the diamond crossings. Which im assuming cuts the power supply, and only momentum keeps the engine going at faster speeds.

Am I right in assuming that the engine should pass power to the tender to counter this? I've identified the connecting pin that jane mentioned and gave it a good clean, the connections appear to line up with the tender but the it will still stop at the exact same place on the diamond crossings, regardless of whether the engine is conencted to the tender. Is there a way to test if the engine part of the loco is passing power through to the tender?

 

Cheers for the help so far. 

 

[96RAF]

If you have the tender connected to the loco and lay them on their side you can use a meter to check continuity across the wheels.

 

The loco and tender left wheels should show continuity with each other and ditto the right wheels if there are pickups on all the wheels of course. Some tender driven locos have pickups on one or both sides of the loco but possibly only one side of the tender (if traction tyres are fitted). You can also check for resistance through the motor from left side pickups to right side.

 

The hypothesis about the post and clamp (tension and compression) is solid as I had a Mallard which was good in reverse but would stall across back to back points going forward. In the end I dumped the electrics across the tender post and installed a four pin plug and socket. Details in my website articles.

[morairamike]

This is the problem I had with tender drive 9F Evening Star. It stalled on diamond crossings for the reason you have given. I cured this by the addition of a wire from the right side brush terminal on the motor through to the right side valve gear on the loco.

On tender drive locos the right fixed slider guide of the valve gear is connected via the con rods and wheel bolts and the wheels, to the track. I soldered a wire to the rear of the slider. Works a treat, loco traverses diamond crossings. Saying that it is now DCC a