DC- Speed matching electric motors

[Lemosteam]

I am thinking of kitbashing a locomotive that will have two motors of the same type inside a scratchbuilt mech.  Is there anything published or suggestions you may have for matching the RPM speed of the two motors without the benefit of a decoder?  Can you describe the methods by which I can determine each motor's respective RPM, what and how to measure them electrically?  I am somewhat electronically challenged, so laymens terms will help immensely!

Any thoughts or help would be appreciated!

[peteski]

If both are identical motors and the gearing is the same for both, then they are already as well matched as needs to be.  Electrically just hook them up in parallel.   I also think that this insane desire for perfectly matching loco speeds is way overblown on the forums.

In my N-Trak days, long before DCC I often ran multiple-unit consists pulling long trains.  Even moderate mismatch between engine's speeds did not have much detrimental effect on the pulling ability, not it damaged the mechanisms (we ran these for hours at a time around a large layout.) Up to a point the locomotives will self-equalize.  Yes, the faster locos will do the brunt of the pulling but that is ok.

As for dual-motor locos, I own a Roco European articulated dual-diesel loco. Each permanently coupled loco has a motor in it. Roco's solution for perfect speed match is . . . .  couping those motors with a drive shaft (with U-joints on each end)!  How's that for simple solution? 

How about your design? Would it be possible to just use one motor and just using a drive shaft to power the other end?

But like I said, if the motors and gearing are identical on each side then you have already done the matching.

Since you are a car guy, compare your design to a dual-engine dragster or a monster car.  How do they speed match those monster engines?  I don't think they use anything fancy - they just mechanically couple them together. Don't they?  In your example, the wheels and track is a mechanical coupling (with a capacity to slip if needed). 

[Lemosteam]

peteski, how did I know you'd be the first to reply? (glad for that!)

The loco I am thinking of will want two separate motors for effect- slippage on one set of drivers vs. the other.  I was kind of hoping someone might imply that because the motors are identical that they will behave the same.  I would like to confirm that for this model (is there a way to do that with a multi-meter?), but generally I agree.  Packager space will be limited so I may have to flip one motor opposite and reverse polarity, so hopefully that won't be an issue?

I also agree with the speed matching comment- I used to quad head locos of different styles and manufacturers all the time.  The only time I had coupling isses was on the bad grade crest on my layout.

[peteski]

John,
I'm still not sure what you're trying to accomplish.  I'm not sure why you want to actually show slippage. Is this going to be a model of an articulated steam loco and you would like one of the engines to visually show slippage?

Assuming that this is your goal and each engine is powered separately, then I would say that the loco will behave similarly to the real 1:1 locomotive. The slippage of one of the engines would occur if it lost adhesion to the track (for whatever reason that occurred). But I think that in 1:160 world, this effect would be greatly diminished.

If you want the slippage to be constant, you could slow down one of the motors by installing a resistor or a diode voltage-dropping circuit in series with one of the motors.

As far as measuring slippage, I suppose you could measure current drawn by each motor (using 2 ammeters).  If the current consumption of the motors was quite different, that would indicate that one is slipping.

If the motor in each end is installed off by 180 degrees then I think you will have to flip one of the motor polarity (you will be able to tell if that is needed since if they are wired incorrectly, the locomotive will just spin its wheels not going anywhere, assuming that there is equal weight distribution over each engine). 

[Lemosteam]

The loco I am thinking of is a solid frame two engine loco (I don't want to reveal just yet).

I am hoping that the motors will perform close enough to not fight but allow the occasional slippage at startup.  I don't think I can accomplish that with a single motor with a common shaft. 

Can I measure the two motors without load?

So I am measuring amps at a common voltage?  I assume I measure this by touching the brush caps? Sorry I'm so ignorant on the subject!

[peteski]

John,
I think you are really over-thinking this.

If the motors are identical then there really isn't any need to measure their performance. Even if each is slightly different, that will not make any appreciable difference if they are both independently power the same type of gearing in the same chassis.

Think about this: imagine that each engine (motor/gears) on each end of your model are each like a DC loco in a standard multi-unit consist.   Even if they are slightly mismatched (which they shouldn't be), they'll still run fine.

To reiterate, your setup would be equivalent to you running 2 identical DC locos in a 2-unit lashup on a DC layout.

As far as electrical connections go, both motors will be wired to the track in a way similar to 2 individual DC locos running on the same track (parallel connection).  If you want to bother to measure the current consumed by a motor, you need to disconnect one of the leads feeding power to the motor and hook the ammeter in series with the motor brush and the lead you disconnected.

Like this:
Before installing ammeter
Left track <------------[ motor ]-----------> right track

After hooking up the ammeter
Left track <--------------[ Ammeter ]------------[ motor ]-----------> right track

(BTW, the ammeter will work just as well if it is installed on the right track side.)

But to get any meaningful results you would need to monitor both motors at the same time.  Honestly, don't worry about the mismatch and just build your locomotive and try to run it.  Like you said, the motors and the gearing is identical on each side.

[Lemosteam]

peteski,

I think I am too, but when I get the chance to learn from you, well, I'm gonna take it.   

BTW is this the SLOWEST DCC/Electronics forum you have ever seen???

[peteski]

What do you mean "SLOWEST" DCC forum? I think that you and I are doing a good job of keeping it lively! 

[One of One-Sixty]

Time to hijack this thread, I have been thinking of the same thing, but with each motor at opposite ends of the train, kinda like a helper engine at the end of a long coal drag.

I am using two Kato RDC-1 mechanisms for my project.

peteski: With what you are saying, my best bet is to make sure the one motor that is pulling the train slightly fast should be the lead correct?

But if I was to add a decoder to each end, is it possible to speed match them?  Or just assigning them the same address should suffice?

[peteski]

Time to hijack this thread, I have been thinking of the same thing, but with each motor at opposite ends of the train, kinda like a helper engine at the end of a long coal drag.

Is this for your Metroliner?  If is, are you sure you need 2 powered units?  I would do what Kato does for their Shinkansen sets or Bachmann for their Acela set: put a single powered unit in the middle of the consist. The end units are unpowered.


I am using two Kato RDC-1 mechanisms for my project.
peteski: With what you are saying, my best bet is to make sure the one motor that is pulling the train slightly fast should be the lead correct?

That was valid for regular trains with multiple locos pulling. If you have power on both ends then speed matching becomes more critical. If the mismatch is too great you'll end up with your train off the track on a curve.  I don't have much experience with end-unit helpers but I think that in that case the slightly faster loco would be better on the end.

But if I was to add a decoder to each end, is it possible to speed match them?

Yes.

Or just assigning them the same address should suffice?

If both powered units are identical and so are the decoders then having them on the same address IMO would suffice.  Again, if this is the Metroliner, I would think one mid-train powered car would suffice. Heck, you could have 2 mid-train powered cars without any worries about speed matching! 

[One of One-Sixty]

peteski Thanks, at some point I will be adding DCC so I am planning for future expansions.  I thought about having a power car in mid-consist, but since I will Amfleet cars crammed in the middle of the two Metroliner shells, it would be hard to disguise the motor and everything in an Amfleet car.

I am still thinking of maybe only having one Metroliner powered and just take the motor out of the other end.