Large Scale Central

Aristo RDC3 stuttering

After years of looking I was finally able to buy an Aristo RDC3. It is like new but it is stuttering at slow speeds and I do not know why. I had the whole thing apart to refasten a couple of doors and a window that had popped off and the electronics looked good and all the plugs were tight. I checked the trucks and there is plenty of grease and they look hardly run.
I use a Revo base unit and at 30% it starts to move but it stutters all the way up to 70% and it smooths out at 75% and above but that is too fast.
What is going on here? Is this common with these? Is there a fix? This thing appears to be so new that maybe it needs to be broken in? Yes I did add the Euro diesel sound to it. :grin:

Any ideas as to what could be wrong?

Does your RDC3 have factory incandescent head lights and interior lamps or LEDs?
Did you try to run your unit with the lamps off to see if it makes a difference?

I will have to try that.

Dirty wheel contacts.

The wheels are like new.

I put a volt meter on my test track rollers and the sound starts at 5v and the wheels start to move at 6v which is not bad but to really get them going it is double the voltage plus.
I tried shutting off the lights and the stuttering still happened?

Sounds like you will need to open the patient up and explore.

I don’t recall how the RDC grabs power from the wheels. Most likely it’s carbon plungers hitting the back side of the wheel. If the unit was over lubricated, or oiled in the wrong spot, you might have fouled pick ups which could explain why it performs well at higher voltage.

The other possibility is a loose wire or an intermittent short. If you have a meter on your power supply, does it spike current when the RDC stutters? That would indicate an intermittent short.

Once you figure all this out, rotate one truck 180 degrees and it will track much better in curves. Only one axle in the truck is sprung and Aristo puts the trucks on so it’s the inboard on one track and the outboard on the other. I thank I have that right. In any case, spinning one truck helps.

The Aristo 2 axle motor blocks in the RDCs do not use carbon brushes at wheel backsides to pick up track power from the rail heads. From what I have seen, it has whisker wires embedded in the motor block grove where the fixed axle bearing resides.

Is the Revolution base station used to power the track in PWM mode? If so and your base station has low pass filter, try it in Linear.

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Rotating the truck will cause a short won’t it? This RDC is more sensitive to crooked track than my other trains. It might be that it is top heavy or it could be the loose motor blocks. I’m not a fan of the Aristo blocks with that wiggly differential case. On this RDC the moving differentials are both facing to the inside. My one other Aristo engine a RS3 has both differentials pointing toward the front of the engine.

Ted D is correct, this RDC has wires inside the block that pick up the power not plungers that ride on the back of the wheels.
When I had it open the wires and boards looked like new but it could be a loose wire.

You are correct Ted about the pickup wires inside the motor blocks.

I had to get the PWM base station to handle the amps but the PWM was giving my older sound systems fits so I bought a converter to make it Linear. Maybe the Linear is causing problems with the RDC? but then again my test track uses a Sounder transformer which I believe is Linear.
The guy I bought it from said that it was surging. A customer in his shop said that he had a RDC and his did the same thing.

Turning off the lights didn’t help. If tomorrow isn’t raining I will bring it outside for another test.

Your assumption on polarity would be correct. I don’t remember if I rotated one or both. It’s been 10 years. If it was just one, I probably flipped the wires around too.

And the idea is to get the floating axles on the outside so the longest wheelbase is sprung, not rigid.

Thanks Ted for the correction on the pick-ups. I was confusing the RDC block with a Bachmann diesel trucks.


So as I understand, the stuttering happens on both your layout with the Revolution base station with it operating in linear and the test track setup with Sounder transformer that is thought to have a linear output.

I suspect you don’t have an oscilloscope, so while the RDC is stuttering on your test track with power applied, place and hold your voltmeter across the track rails and observe if the voltage is steady, not changing too much (how much?). You may need to use alligator clip leads to connect the voltmeter leads to the rails so you can be sure any voltage change is not due to trying hold the meter leads against the rails that can easily happen and fool oneself.

I am trying to determine if the power source is varying in concert with the stuttering. I had experienced this issue that I call motor surging with my Aristo RDC1 that is the result of how its internal regulator (PIC processor software and circuit) was ill functioning - design flaw under certain conditions. I don’t know if the RDC3 has the same PIC processor circuit.


Ted I thank you hit the nail on the head there was some with the same PCI processor circuit.

I think you are on to what I suspected Ted, that the board in the RDC is causing the stuttering/ surging. I have a Bachmann Railtruck that does the same thing but I think that has to do with the drive train, or does it?
I tested the RDC again on my main line with the linear power and it was surging at low speeds. I also bypassed the linear converter and put PWM to the track straight from the Revo base unit and the RDC did the same thing. The PWM is weird in that it affects my old Sierra boards, in my S4 the horn kept sounding and the NW2 on the same track the lights were not working? That is why I went back to Linear power.

I also tested the RDC on my side yard which is isolated from the main line and uses a LGB starter set pack. The RDC was surging there too and it needed a lot of power to move. I feel if I kept pushing it the thermal shutdown would have kicked in.

I also tested the volts as you suggested Ted. At 5v the sound kicked on, at 6v the RDC started to move and up to 10v it was still stuttering and it had to go over 15v to run smoothly. I made a video I will try to attach.

I do think it is the circuit board that is causing the problem. What can be done to fix that?


To do the test, only use linear and set the track voltage to some fixed value and keep it there when the motors are stuttering (I call surging ) and see how much the voltage changes across the track when the surging happens.

When I was working on my RDC1 (which can have different circuitry than the RDC3, including LEDs for lamps) I made a couple of videos concerning how the Aristo DC to DC converter used for powering lamps is done with the PIC processor in the RDC1 . To control / limit light intensity, the PIC processor via software produces a PWM waveform across the lamps when starting somewhere around 6 volts dc and then at a greater voltage where it should be expected to. In my RDC1 case, the problem is that the PIC processor would start to wake-up some where around 6vdc across the tracks and then go into reset mode induced by the high turn on current for the incandescent lamps affecting the power source at the tracks (the 6 vdc or so across the tracks would drop in voltage). This would result in periodically occurring motor surging.

(Again, I don’t know what circuitry the RDC3 has and if it has the same PIC processor.)

I made a couple of videos about it:
Be forewarned, videos admittedly were done with poor camera skills.


“Aristo RDC1 Motor Surging Mitigation”:


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Thanks for all the info Ted. I did setup the volt meter on the track in Linear mode and watched if the voltage jumped up or down with the surging but it did not.
My RDC doesn’t have that big board on the floor like yours does. I wonder if mine us a newer unit and they reduced the size and stuffed it all into the ceiling?
There are LED’s in there and now I’m wondering if there are also regular bulbs too? Maybe they are the problem as they were in yours?
I’m going have to watch your videos to the end when I get a chance and then get back into my RDC and find out what it going on.

Thanks again.

Watching your video Ted it looks like you were able to limit the surging by removing the regular bulbs and replacing them with LED’s. I just had a look at my RDC3 and all the lights are LED’s. I don’t think that troublesome board you have is present in mine.

I might just have to run this unit at faster speed than normal and live with the surging at lower speeds.

I have an honest and simple question to ask since we are so deep into the electronic aspect of the stuttering on the RDC3.

Quoting you Todd… { I checked the trucks and there is plenty of grease and they look hardly run. }

Now to :rooster: 's question…Did you “open” up/take off the bottom covers on the motor blocks and actually look at the GREASE or perhaps PUTTY (by now) on the gears or did you just look at the grease on the trucks?

If not perhaps you might want to do that?

Just saying …and I got no skin in the game but sometimes simplicity is often overlooked.

Yes I took them apart and it was still grease. Thanks for chiming in and you are correct that sometimes it can be something very simple that causes us all fits. :upside_down_face:


I think it’s worthwhile to see if one truck (motor block) runs different than the other.

I suggest putting the RDC3 on Bachmann rollers ( if you have them or similar - which fasten to the track) and see how each motor block runs by watching the wheels go around with the base station starting out with low voltage, and then progressively increasing it. (Compare the 2 motor block’s wheels rotation to see if different.)

If you don’t have the rollers, the RDC my have pig tail connectors coming out the ends which is used for battery operation, but you can apply track power with clips to pins of one of those connector. With the RDC on its back, set the RDC slide switch to Battery and watch the how the wheels operate on each truck.

BTW, Does your RDC3 have traction tires on one of the axles of each truck?


The RDC has been running better. I wonder if this used piece is newer than suspected and needed to be broken in?
I did as you suggested Ted and one motor block starts turning at low voltage before the other.

There are no traction tires.