Interaction between motors

[Guest]

My layout has a 6-car Bil/Hal and an 8-car Cor formation which have three and four Hornby motor bogies respectively.  They run excellently most of the time but occasionally slow almost to a standstill, especially when running down a gradient on a moderate controller setting.

It seems to be some kind of interaction between the motors as a single unit will run perfectly over the same routes but I do not know enough about electrics to understand exactly what is going on.  A multimeter placed across the rails does not reveal anything useful.

Power supply is a simple Gaugemaster 100 series panel-mounted analogue controller with (as I understand it) no feedback.

Any advice welcome!

[kevinlms]

What sort of power supply are you using? It sounds a bit like shutting down due to overload.

[AndyID]

I think you are overloading your controller. It's output is limited to one amp. You could measure the current with your meter IN SERIES with the feed to the track.

[Guest]

Thanks to you both for the responses.  I will check the current consumption as suggested.  I am using a Gaugemaster M1 transformer and a GMC-100 panel controller.

[Guest]

I checked current consumption, it is around 400mA for the four-motor formation,  When the train suddenly slows, the current drawn dips slightly, then increases briefly as progress is resumed.  In both cases we are only talking of 20-30mA either way.

 

The problem is worst when the train is running downhill and at a moderate controller setting.  It never happens on uphill gradients and it becomes less noticeable if the train is driven downhill at full power - but then it hits the next curve at a scale 150mph!

 

Interestingly, the train seemed somewhat better behaved when the ammeter was in the circuit than when it was not.

 

The problem is specific to Hornby motor bogies - I have an 8-car train with four Black Beetle motors and that does not exhibit the same behaviour.  It is a pity as the Hornby motors give silky-smooth slow running at other times.

[AndyID]

55 minutes ago, 34017Ilfracombe said:

I checked current consumption, it is around 400mA for the four-motor formation,  When the train suddenly slows, the current drawn dips slightly, then increases briefly as progress is resumed.  In both cases we are only talking of 20-30mA either way.

 

The problem is worst when the train is running downhill and at a moderate controller setting.  It never happens on uphill gradients and it becomes less noticeable if the train is driven downhill at full power - but then it hits the next curve at a scale 150mph!

 

Interestingly, the train seemed somewhat better behaved when the ammeter was in the circuit than when it was not.

 

The problem is specific to Hornby motor bogies - I have an 8-car train with four Black Beetle motors and that does not exhibit the same behaviour.  It is a pity as the Hornby motors give silky-smooth slow running at other times.

 

So not the current and the voltage from the controller seems to be constant. I know you are running DC but is it possible there are actually DCC decoders in the Hornby units? Some decoders will run on DC but noise from other motors might confuse them.

[Pandora]

You state the issue worsens when the sets are running down a gradient on moderate controller settings. This may be motor imbalance,  a rogue motor unit clashing with the others,  the rogue unit in a form of stall caused by the worm gears to axle gear interaction,   in typical model railway gear trains,  a motor armature can turn the worm and therefore drive the axle gear, but an axle gear cannot turn a worm gear, the gear train will stall.

[stewartingram]

Possibly a pickup problem as the current dips?

[Nearholmer]

I’m with pandora in wondering if this might be a mechanical, rather than electrical effect.
 

I don’t know how any of these motor bogies are constructed, but if the gear ratios are subtly different between them, or the motor winding details, leading to the “slow“ bogie getting dragged ever-so-slightly downhill, there is certainly potential for ‘lock up’ if the armatures have excessive end-float. Even with nominally identical bogies, minor manufacturing tolerances could be enough to cause the same.

 

The same would possibly be self-correcting going uphill, because the ‘fast’ bogies would have additional load thrown on them, and tend to slow down.

Have you tried the combo with the units in the opposite order in the train?

 

And, is the track perfectly clean, so that pickup issues definitely aren’t an issue?

 

’Fighting’ between units used to occur with the real thing under adverse combinations of circumstances, so you may be in good company.

[Guest]

Thanks to everybody for your thoughtful responses.

I am sure there are no overlooked DCC modules as I stripped out the DCC sockets when adapting the donor Hornby 2 Bils for my 8-car Cor formation.

The idea that it is a mechanical problem rather than an electrical one is interesting.  The layout has a return loop so the units are reversed in normal operation but nevertheless I will experiment to see whether it runs better one way round than the other.

The pickup problem idea also merits further investigation.  If there is a slight voltage drop through a dodgy fishplate the leading motor is going to slow down and the other motors might not like it!

Much food for thought and experiment - thank you, experts all!

[AndyID]

I was wondering about a dodgy fishplate too  

 

For running multiple motors as you are you also might consider adding droppers connected to a power bus under the baseboard. It's best not to rely on fishplates for electrical connections. Also nickel-silver rail has a lot more resistance than copper. You could at least try the power bus in the area where you are having the problem. Even if it does not fix it it might prevent a problem in the future.

 

Edit: Another thing you might try  is running the formation but prevent the powered units coupling with each other. That might help to isolate electrical from mechanical effects.

 

 

 

Edited October 10, 2020 by AndyID
More info

[Steven B]

Can you break the train into sections and run just one motor at a time? It might be possible to see if one is causing the problems.

 

Steven B.

[DCB]

What type of power bogies are these?   Lousy downhill running is normal with worm drive power bogies on smoothed DC, the cure is to run on half wave . I occasionally run a Triang DMU coupled to a Lima DMU and they run fine on a Morley except downhill but run fine Uphill on full wave and downhill on half wave on a H&M Safety Minor.   The uneven torque stops the worm drive loading up against the end thrust bearing.       Both these controllers provide a variable voltage not a variable resistance, Morely electronic, H&M autotransformer. Both will provide low voltages off load, the H&M down to about 3 or 4 volts, the Morley to a tiny fraction of a volt

Obviously feed back controllers get totally confused by dis similar motors running together.

 

[AndyID]

4 hours ago, DavidCBroad said:

The uneven torque stops the worm drive loading up against the end thrust bearing.

 

Worm gears do not "back drive" very well but that has a lot more to do with the large gear reduction ratio than anything else. If you make a gearbox from spur gears with the same reduction ratio it won't back-drive either.

 

Any gearing system with a large reduction ratio introduces a lot of friction and there is not much you can do about it. That's why it's always best to use the largest diameter motor with the smallest possible reduction gear ratio.

[DCB]

The old Triang 20:1 worms on the power bogies won't turn the motor no matter how hard you turn the wheels . I have some spur gear drive water valve gearboxes of over 100 to 1 which work equally well both ways.    Its to do with end thrust, the worm wheel tries to move the worm along the axis of the armature at right angles to the direction of rotation whereas a spur set up the wheels are in the same plane as the armature shaft so they turn the armature in the direction of rotation.   Its the same when under power, the worm drive armature turns when power is applied  and the worm tries to push the worm wheel sideways, only when the play is taken out does the worm wheel and wheels start to turn.  That can mean the wheels move quite a way and the armature end thrust is taken on quite a large plain bearing with lots of sticksion so a smoothe start is nigh on impossible. Using a Wrenn motor with ball bearings for armature end thrust and shimming between worm wheel and chassis with dissimilar thrust washers, bronze/ steel/mazak improves the situation but with a heavy train behind them my Triang/ Hornby locos bind up and surge down my 1 in 30 even on quite a lot of power.  Spur gear ones, Hornby Tender drives, Lima etc are almost immune, they will stop eventually but only when the power is turned off. 

Edited October 11, 2020 by DavidCBroad

[Simon G]

My first thought on reading this thread was whether your formations actually need multiple motors to run them?  If you are using the modern Hornby motor bogies, I have found that one of them will run my old Triang Blue Pullman 6 car set perfectly happily.  On occasions I run the set with power cars at each end using the original Triang motor bogies, but the motors do seem to fight against each other at times.  The single motor setup does give smoother running.  If I were you, I would try to disconnect 2 of the 4 motors in the 8 car set, noting that you will need to disconnect them both electrically and mechanically for the set to run OK.

[AndyID]

I suspect the problem would go away if all the motors were connected in parallel with jumpers but it wouldn't be all that easy to implement.

[Guest]

Apologies for my lack of input over the last couple of weeks - real life got in the way!  However I had a chance this afternoon to run some of the tests people have suggested, with interesting, if not entirely conclusive, results.

Firstly,  I connected parallel feeds to the track - no change in the units' behaviour so I think we can eliminate a dodgy conection from the list of possible causes.

Secondly, taking Steven B's suggestion, I split my 8-car Cor formation into four 2-car motor+trailer sections and ran them all down the incline at the same time, separated from each other by about a coach length.  On the usual low power setting one 2-car pair ran marginally slower than the others but, separated from each other, none of the pairs showed any tendency to stall or hesitate.

I then re-formed the two 4-Cor units (M-T-T-M) and ran each as a standalone train - both ran perfectly smoothly down the incline on a range of power settings.

Next I re-coupled the units to each other to see whether the position of the 'slow' motor/trailer pair in the 8-car formation affected the running.  The tendency to hesitate on the downhill returned but it did not seem to make any difference whether the slow pair were leading or trailing (I couldn't put them in the middle of the train as the formation does not have couplers or NEM sockets at its outer ends).

So...I think the theory that there is a mechanical interaction between motor bogies when they are not free to run at different speeds is probably the right one, especially as the problem does not manifest itself on every run and the effect ranges from a silght hesitation to an almost complete standstill before picking up speed again.  As a first step I will look carefully at the 'slow' motor/trailer pair to see whether there is any mechanical impediment to free running, such as an axle tight in its bearings.  Maybe if it can keep up....

I take Simon G's point that fewer motor bogies would normally suffice but these MARC Models etched brass and cast whitemetal kits are rather heavy and my layout includes some stiff inclines and sharp curves - it is not so much that I need the power, more that I need the driven axles to avoid wheelslip.

As AndyID says, the problem would probably go away if I connected the motors to each other electrically - I did do that originally, when the units were powered by Tenshodo 'Spud' motors but the inter-car jumpers interfered with the lateral movement of the cars through crossovers, causing derailments - in fact the whole setup really preferred to go straight ahead in all circumstances!  I could try again, with thinner, more flexible wires, though.

If I did, would I need to connect both sides of the motors or would a single wire do the job, relying on the track for the return?

DavidCBroad's suggestion of using half-wave rectification takes me well beyond my knowledge of electrics - how compatible would this be with my other motor types, which range from 1950s Hornby Ringfield motors via Anchoridge open-frames and Black Beetles to modern Hornby and Bachmann types?  I have a very 'plain vanilla' setup of Gaugemaster transformers and 100-series controllers which have, as far as I know, no feedback.  This specific problem apart, I am very happy with the way everything runs.

Once again, thanks again to everybody for your thoughtful and constructive responses.

[AndyID]

As Hercule would say, "Ze plot thickens"

 

More questions:

 

Are all the power bogies nominally identical? (same gear ratios, same wheel diameters)

Do any of them have traction tires?

Can the power bogies be easily removed from the coach bodies for testing or is that a pain?

Is your meter analogue or digital? (for measuring the current analog would be better - digital meters can have a slow reaction time)

What happens if you "assist" each powered unit by pushing it to make it go a bit faster than it wants to (does the gearing tend to "bind up"?).

 

 

Edited October 22, 2020 by AndyID

[Steven B]

Do they have the same motor types? Cleaning/servicing the commutator & brushes could help. It might also be worth checking the resistance of each motor. If one's significantly higher or lower than the others it could have an impact on the current available to each motor when running them together.

 

Steven B.

[Guest]

Not sure if I should respond to AndyID’s Hercule Poirot in the character of Captain Hastings (“I say!”) or possibly Miss Lemon?

 

All the motor bogies are from donor Hornby 2 Bils, bought at the same time and identical as far as I know.  The only modifications are cosmetic - Cor-type equalising beam bogie sideframes - but these do not touch any of the moving parts as the bogies have inside bearings.

 

No traction tyres.

 

Removing the motor bogies would be a bit of a pain as it would  involve unsoldering the connections to the trailing bogie pickups but it would be do-able if worthwhile.

 

My meter is analogue and of a certain age.  My fellow Club members think Noah used it to set up the electrics in the Ark.

 

Pushing the train down the incline is an interesting idea - I’ll give it a try and report back.

 

I will also try measuring the resistance of each motor as Steven B suggests.

 

More anon.

[AndyID]

3 hours ago, 34017Ilfracombe said:

My meter is analogue and of a certain age.  My fellow Club members think Noah used it to set up the electrics in the Ark.

 

 

Pay no attention to them. If it's an AVO is a real "keeper". (As opposed to "kipper", in which case Hercule would have said something was a bit fishy   )