RailPro User Group

RailPro => RailPro Specific Help & Discussion => Topic started by: Tom on July 30, 2018, 05:30:41 PM

Title: MOTOR FULL LOAD CURRENT
Post by: Tom on July 30, 2018, 05:30:41 PM
I have come to learn that there are at least several electrically knowledgeable posters on this site.

For some time now I have experienced that when linking two or more locomotives together after having set the Motor Full Load Current automatically they will not stay the same distance away from each other when not physically connected.  Sometimes it is not even close.

Having determined by trial and error that two locomotives will maintain an equal distance from each other at all speeds when the mA are about 200mA apart I manually set one locomotive 100mA above its automatic mA and the other 100mA below its automatic mA.  Which leads to some questions an electrically challenged RailPro user has:

•   Why does setting the Motor Full Load Current automatically not work as it is supposed to work, at least with regard to when it comes to linking two locomotives (both Athearn Genesis GP9) to work with each other?

•   Is there a much simpler methodology that RailPro users may have developed to get locomotives to run at the same speed when linked?

•   The most important question is what possible damage is likely to occur by setting the Motor Full Load Current manually 100 mA or more from the automatically developed one?

Tom
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on July 30, 2018, 06:27:00 PM
If your GP9s are new I would break them in well and see if the problem doesn't go away by itself.

It has been my observation stall current readings are different each time I test. Not by a huge amount, maybe +-50mA. Why, I don't know. I confirmed with my ammeter that a loco does return different readings at wheel slip under what otherwise seems identical test setup. So, it is the locos not the HC. I attribute it to the fact they are toys, not precision machinery. I do the auto stall test several times noting the reading. Then I average the readings and use that.

Note the stall reading during repeated tests of each GP9. Do the same loco results vary by a large amount?
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Tom on July 30, 2018, 08:31:29 PM
Alan,

I agree with your stall limit test variations observations and have wondered if the motor temperature could have anything to do with it; among other potential variables.  Variations are within the 50 mA +/- range you mentioned, but that does not explain or address the speed variation between locomotive using the automatic setting of the load current.  It seems that if the automatically set load current is as reflective of locomotive performance as Ring says it is, it should work – within reason.  I am a little disappointed that the automatic load setting does not work entirely well for whatever reason.  GP9s are not new and I have no idea how used they might be and Ring is definitely oriented towards diesels as well as newer versions, so maybe older HO motor electrics are a problem for Ring in this regard?

Do you have any comments on how to easily get all locomotives running at the same speed (top speed changes have little or no effect) and whether or not they could be damaged by setting the load current manually too far from what the automatic comes up with?

On another related BTW issue, when locomotives are linked the overall speed at a speed % is less than for each locomotive individually not linked.


Tom
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on July 30, 2018, 09:34:20 PM
To be honest, I have never ran two locomotives uncoupled to see if they maintain spacing although Ring does just that on the promo video. I have not had unusual gear wear, coupler breakage, or anything of the sort that would indicate the locos aren't playing well together. My layout cannot be powered up at the moment (in the midst of fascia panel installation, lots of bare dangling wires) so I cannot test maintaining spacing of locos for you.

I don't believe you will damage anything regardless of stall current setting. Even if full track voltage with unlimited amperage supply was applied to the motor (DC mode) you would not damage it. It would just take off at 90 MPH! The LM has internal over current protection so you won't damage the module. It will simply shut down if overloaded. If greatly different stall current settings makes the locos run nicely together then I would do it that way.
 
Yes, I too have noticed the throttle position difference between single loco and multi-loco consists although it is a small difference. I have no explanation for why that is.

Curious, what stall current do your GP9s measure? 100mA is a big difference on a 300mA loco but a small difference on a 900mA loco.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: KPack on July 30, 2018, 09:59:16 PM
Keep in mind that load sharing is not speed matching.  It is very likely that two locomotives will run at different speeds when uncoupled.  Think about it....the principle of load sharing is based on the locomotive modules detecting a load, and then distributing it across the consist.  If a lead locomotive isn't coupled to anything, then it detects no load, and therefore tells the following locomotives to contribute less to the overall pull.  So yes, the following locomotive will usually run much slower than the lead if they are uncoupled.  How much slower depends on the individual locos and their settings.

You'll notice that the effects of load sharing are much easier to see when pulling a longer/heavier train.  Try it and you'll see.

That being said, there have been a couple of locomotives I've built and installed Railpro in that I had to dial in the MFLC manually in order for them to play well.  These were frankenstein locomotives though....motors were not original and much work was done to the drivetrains. 

Also, going along with Alan's comments, I will typically run my MFLC settings three times on a new locomotive to get the most accurate one.  Does it really matter?  Probably not, but I do it anyways.  If you think about it, the MFLC will drop slightly after first time due to the wheels/rails getting mildly polished from the spinning.  Running the locomotive for a bit beforehand to warm up the motor and loosen the gears a bit may also make a difference.  It will likely be a small difference, but a difference nonetheless. 

Out of curiosity I have re-run the MFLC on locomotives that had it set years ago, and remarkably the values have largely been the same, maybe within 10 mAh of the original or right on.

-Kevin
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Dean on August 01, 2018, 09:09:59 AM
With new locomotives, I set the full load current using the automatic mode. Then after running my break-in routine, I measure the full load current again. Usually, there is a drop in the full load current.
Running a four or five engine consist pulling 30 heavy cars, ( 8 oz+ each ) I watch the couplers. The couplers on the locomotives stay tight, going up or downhill.

My break in procedure:

 The main thing you are trying to accomplish during a break in of a DC motor is to seat the brushes and polish the commutator.

The armature ( the entire rotating part of the motor including the commutator) moves back and forth in the housing as the speed and load changes.

Getting the brushes to seat is pretty straightforward. Run the engine at varying speeds in both directions for about 20 minutes each direction.

Getting the proper polish takes current passing from the brushes to the commutator and running unloaded doesn't supply enough current. After running light as above, I attach a coal car to the engine that is half full of lead shot. This gets the same 20-minute treatment as the engine running light.

I checked the current draw of some Kato powered engines by placing my finger in front of the engine to prevent it from moving and ran it at full speed for a few seconds. The wheels were allowed to spin on the track. New, out of the box, most engines drew 270ma to 310ma. After break-in, they would draw 220ma to 260ma. Of course, the gearboxes and other running gear also got some break-in time too. But with Delrin plastic in the gearboxes and running gear, I don't think they made much difference.

[ I was an electrician in a rolling mill for 35 years. Over 90% of the motors in the plant were DC. My break in procedure is based on my experience working on these DC motors. ]

Title: Re: MOTOR FULL LOAD CURRENT
Post by: G8B4Life on August 01, 2018, 09:30:35 AM
Going to do a bit of a thread hijack here, but it is relevant to the discussion.

After reading this topic I decided to look at what the Patent had to say about the load sharing function, which is very little with only a little bit of information on one part of the logic.  You can easily look it up if you want, I won't put it here as it's not the point of my post.

What I did read which I found strange was the way the modules control the motor. We all know the DCC waveform is square wave right? I've never put an oscilloscope on anything let alone a DCC decoders motor output but I've always assumed that that would also be square wave as well, all the PWM motor control that I've read about is all square wave. Well it appears that Ring has done it differently. From the Patent:

"wherein at least one control module varies a voltage on a motor of a respective motor powered rail vehicle in accordance with a periodic wave shape of a subsonic type between about 2 and 20 Hz with an approximate triangular shape"

What would be the benefit of driving a motor with a triangular waveform (disregard the word approximate for this question)? From what I can gather from reading the above it looks like it's easier to "set" the average voltage that the motor sees without having to drive the output transistors at supersonic speed like modern DCC decoders have to but that's the only thing I can think of.

- Tim
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 01, 2018, 10:17:17 AM
... What would be the benefit of driving a motor with a triangular waveform (disregard the word approximate for this question)? From what I can gather from reading the above it looks like it's easier to "set" the average voltage that the motor sees without having to drive the output transistors at supersonic speed like modern DCC decoders have to but that's the only thing I can think of.
- Tim

Fewer parts count in the module. The triangular (dual log slope) waveform is the natural output from an oscillator due to timing network charge and decay of C. Wave shaping to a neat square wave requires several more components i.e. triggers. The additional wave shaping provides little benefit to motor control because of the motor's rotating mass relative to the signal frequency. The motor couldn't respond accurately to the sharp rise time of a square wave anyway so a slow rise/fall wave works just as well. There is a power loss using a triangular waveform versus a square wave however that is easily compensated with higher frequency.

Voltage across C over time:
wave.png

To further hijack the thread, this subject will come into focus when I post my DCC-simulated power supply circuit for Jacob.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: KPack on August 01, 2018, 10:21:14 AM
I'm so confused, lol.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 01, 2018, 10:36:52 AM
I'm so confused, lol.

That's why the magic is always kept inside the box out of view!  ;D
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Dean on August 01, 2018, 05:23:44 PM
Would this explain why a DC only locomotives buzz when they are put on a DCC track?
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 01, 2018, 06:36:17 PM
Yep. That and a DCC signal is AC so the poor DC loco is trying to reverse directions 7,000 times a second. That's why they get hot.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: TwinStar on August 01, 2018, 08:44:29 PM



Voltage across C over time:
wave.png



The last time I saw this there were sharks and tornadoes coming out of it. That's my level of electrical knowledge.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: G8B4Life on August 01, 2018, 10:41:09 PM
Thanks Alan, I was hoping you'd be able to provide an answer.

It makes more sense now. When I read the words "approximate triangular" I envisaged the typical straight sided sawtooth pattern that one sees all the time in images, perhaps "flattened" on top by the word approximate, not a log slope.

With the dual log slope waveform, how much harder is it to work out what the average voltage the motor sees is compared to a square waveform (which is easy)? Given the "1000 speed steps" we have the 2 to 20Hz duty cycle mentioned in the Patent doesn't sound like it'd give that.

- Tim
Title: Re: MOTOR FULL LOAD CURRENT
Post by: nodcc4me on August 02, 2018, 06:19:33 AM
Kevin, Jacob, you are not alone. If Alan and Tim ever got together and started talking electronics there would be a lightning storm, the likes of which the world has never seen.  :o
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 02, 2018, 07:27:33 AM
... With the dual log slope waveform, how much harder is it to work out what the average voltage the motor sees is compared to a square waveform (which is easy)? Given the "1000 speed steps" we have the 2 to 20Hz duty cycle mentioned in the Patent doesn't sound like it'd give that.
- Tim

Finally, a use for that Integral Calculus class you took at university years ago!

calc2.png

Close enough to a sine wave to use RMS or 0.707.

Why do you think we can't have 1000 steps? Cycles per second don't have to be integers. I would lay odds it is actually 1024 speed steps since it is a digital system.

Title: Re: MOTOR FULL LOAD CURRENT
Post by: G8B4Life on August 02, 2018, 09:01:24 AM
Finally, a use for that Integral Calculus class you took at university years ago!

You have the wrong idea of how far I made it through schooling.

Quote
Why do you think we can't have 1000 steps? Cycles per second don't have to be integers. I would lay odds it is actually 1024 speed steps since it is a digital system.

I'm not saying that I think we can't have 1000 speed steps.  I was saying that with my very limited knowledge of PWM the face value of the information presented to me made it sound like it was not possible given the duty cycle range, not that it wasn't possible.  Now that I know that cycles per second doesn't have to be an integer (I've never seen any reference to it being anything but an integer in any PWM related information I've ever looked at before, it's always shown and written as whole numbers) it now makes sense that there can be 1000 speed steps within the given cycles per second range. In my effort to understand this I've probably got a bunch of other things wrong so I'll just stop now.

- Tim
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 02, 2018, 09:58:58 AM
Neither frequency nor pulse width are limited to integer values. Either or both can be real numbers.

Think of it this way... FM radio signals are similar to PWM ( I said similar  :) ) except sine instead of square. The FM signal is modulated to represent the audio spectrum (or at least some of it). In this case there is a near infinite number of possible frequency divisions. It is just a matter of how many places to the right of the decimal point you can measure.

Clearly this is the case with RP. As you note, with a bandwidth of only 18Hz the "steps" must be real numbers else with integers we would be limited to 18 speed steps. Which BTW sounds eerily similar to the old 14 step DCC.

As this conversation drifts deep into the weeds it is worth mentioning there are two controlling parameters to square wave PWM when also used to convey control signals (DCC track) - pulse frequency and pulse width (percentage). Obviously at 0% and 100% pulse width there is 0 frequency thus no control signal conveyance. But for everything in between the pulse width conveys digital info while the frequency and width combined determine the total power delivered over a given time period. At the motor output of a module we have no need to convey information so frequency and/or pulse width modulation will do just fine.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Tom on August 02, 2018, 06:14:56 PM
I am happy to learn that manually setting the MFLC to anything will not harm an HO locomotive motor.

I should say I have had only a very few problems when consisting multiple locomotives, mainly uncoupling in certain circumstances due to one pulling or pushing slightly harder than the other.

Having said this, it is still demonstrable that linked but separated locomotives, mine anyway, will not stay the same distance apart by using the automatic MFLC.  I got all locomotives to run close to the same speed, that of about a 45-50 MPH scale speed, by trial and error starting with 3 locomotives and manually adjusting the closest two and then getting each additional locomotive in sync with one of those.

Having accomplished the above it is still noticeable that some locomotives move sooner and start faster than the others and travel at slightly different speeds at different throttle selections.  Overall I think they run more smoothly together, but would not want to do what I did with too many locomotives.

Most of the complex electrical comments in this thread are beyond my electrical level of competence, which is close to zero.  I still do not fully understand the differences between DC, DCC (never used DCC) and PWR-56.  Can someone provide a short lucid tutorial in laymen’s terms: from above comments, a PWR-56 is DC current, DCC is AC current, and Ring modules will run on both DC and AC powered track.  But do not run ring modules using a DC power pack with the throttle set at full speed.  Never mind for now the signals running through the tracks for DCC control.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 02, 2018, 06:47:21 PM
A picture is worth a thousand words, right? Perhaps this illustration from an old thread will help you.

The top row illustration is a conventional power pack. Notice the constantly fluctuating bumpy output. That is bad for modules. Hence the recommendation not to use power packs with LMs.
The middle row illustrations are DCC at various points in the current path. Left = signal on DCC powered track, Center = rectification inside the module, Right = smoothing inside the module.
The bottom row illustration is the output of a PWR.

Yes, the horizontal axis for zero volts is missing on the last DCC graph. My bad.

waveforms.png
Title: Re: MOTOR FULL LOAD CURRENT
Post by: KPack on August 02, 2018, 10:37:48 PM
Regulated DC for the win!!!
Title: Re: MOTOR FULL LOAD CURRENT
Post by: TwinStar on August 02, 2018, 11:38:30 PM


Having said this, it is still demonstrable that linked but separated locomotives, mine anyway, will not stay the same distance apart by using the automatic MFLC.  I got all locomotives to run close to the same speed, that of about a 45-50 MPH scale speed, by trial and error starting with 3 locomotives and manually adjusting the closest two and then getting each additional locomotive in sync with one of those.

Having accomplished the above it is still noticeable that some locomotives move sooner and start faster than the others and travel at slightly different speeds at different throttle selections.  Overall I think they run more smoothly together, but would not want to do what I did with too many locomotives.



Tom:

I think you are completely misunderstanding the key difference between load sharing and speed matching. I wouldn't expect any uncoupled and linked locomotives to ever maintain a given distance between them. Real locomotives don't start in uniform unison. They bang and clang against each other until they get a 'feel' for who is doing what. Speed matched RailRro locomotives, unless I'm completely in error, is just wrong. The locomotives need to be coupled to each other, they need to be linked, and they need a good MLC to operate correctly. If your lead Atlas unit is dragging at 20% power it's going to communicate to the trailing P2K to give a little more. And similar adjustments will be made throughout the power band. The locomotives need to feel, I think through BEMF, and communicate to operate correctly.

I might be wrong but I think the rest of us are running RailPro correctly while you're trying to DCC Speed Match them. More informed comments will be coming from others shortly.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 03, 2018, 06:47:23 AM
I concur with the group - speed matching and load sharing are two different animals. The module knows the load because it can measure motor current. It has no way of knowing speed. There is no rotation sensing of motor or wheels going on. No speedometer.

Although........... at 10:15 in the video. I suspect prior to making the video the locos were speed matched like Tom's locomotives. Marketing, not to be confused with reality.  :P

Title: Re: MOTOR FULL LOAD CURRENT
Post by: Dean on August 03, 2018, 09:41:04 AM
Almost all my RailPro engines are in 4 or 5 unit consist. When they first start moving there is a few seconds where they appear to 'hunt'. After that, they all run with tight couplers. The controller needs feedback before it can start controlling the engines. Running them uncoupled is fruitless. The current draw per engine is so low it would be extremely hard to control them.
If you have engines that have large differences in full load current, one or the other could be out of the control range of the controller. My Atlas Trainmasters and Stewart 'F' units are that way. On top of that, the Stewarts are 20 years old and the Trainmasters are ~5 years old. I can run them together but it seems that it takes longer to get them to settle down. Slow speeds are worse. Once they come up to speed they run fine.
The engines that always run together I have tuned to make them run even better. I set the accel rate and the decel rate the same on all engines. I found through some experiments the controller overrides these settings but having them set the same makes them easier to control...my opinion. I make sure the top speed and current settings are all the same. But, these engines are the same make and model and the same age.
 
Title: Re: MOTOR FULL LOAD CURRENT
Post by: G8B4Life on August 03, 2018, 10:08:56 AM
I think Jacob might have it with the understanding of load sharing and speed matching. RailPro is designed to share pulling power when MU'd, not to go at the exact same speed as each other (though they go roughly at the same speed when MU'd). As someone previously mentioned this is likely why load sharing doesn't work as well with MU'd light engines as opposed to hauling a train, with light engines there is nothing to share as the locomotives are each pulling only themselves.

I pulled this info (tidied it up a bit) from the Patent tonight. It relates to load sharing.

"Direct bi-directional RF capability allows Multiple Unit consisting of locomotives that can be controlled as one while being coupled together. With that said, the lead locomotive can be using open loop control with just a reference command signal to adjust to. The locomotive motor power can be monitored by the control module in the locomotive and sent to follower locomotives. All follower locomotives would be configured for closed loop power regulation to match the lead locomotive. All locomotives in the consist will then pull with the same power and self regulate for variables that change load on the consist; such as overcoming static friction during movement initiation, trailing model railroad cars forming a train that maneuvers through vertical and horizontal curves, change in track voltage at various locations of the layout, etc. The designated lead locomotive can transmit the information directly to the followers, transmit to them through repeaters, or transmit the info back to a controller that can then pass the information to the followers."

and

"The power values of the motor loads are defined or measured by a motor current. One of the controller and the at least one control module execute a predetermined logic including at least one of a drop power calculation by way of multiplying motor current squared by resistance and motor losses represented by power loss in windings of the motor. At least one control module is configured to use the full load power value at full slip of a respective vehicle as a close equivalent of a full power value of a respective motor. At least one control module is configured to receive a preselected power value so as to maintain tension between couplers of the at least pair of rail vehicles."

and

"When considering the static friction of a consisted, multiple locomotive train, getting it started in motion takes substantially more power than it does to keep it moving at a specified speed. With that, an advantage exists when using bi-directional communication between the locomotive control modules and sharing the power value between the consisted locomotives with only one known parameter stored in memory, that is the full power value at full slip. Full slip is defined when maximum control system voltage is applied to the locomotive motor through the control module and it is held from movement with only the locomotive weight affecting the vertical load on its wheels. When the locomotive is in the "full slip" state, a motor "full power value" is stored in memory thus characterizing that particular locomotive motor. When used in practice, the designated lead locomotive would be sent a reference command signal from a controller in which a locomotive motor power value would then be measured from the designated lead locomotive's motor by the control module and relayed to the follower locomotive(s). By doing this continuously, the follower locomotive(s) will follow the lead locomotive's power reference and automatically regulate to share load about evenly through the breaking of static friction, curves, turnouts, and any other cause of load changes affecting the model train. As an example, when the lead locomotive is sent a reference command signal to begin movement, its motor power will increase until static friction is broken, then the motor power will reduce in order to maintain a steady roll. Since the follower locomotives are continuously receiving the lead locomotive's motor load value, they too are continuously adjusting for a good match in pulling power. This match is simply a percentage of full motor power for each individual locomotive as defined when they had their full load motor value stored in memory during their full slip calibration. This series of control steps allows for better and more accurate control during very low velocity train movement as well as it self-compensates for consisted locomotives with different motor characteristics, differing gear ratios, differing internal and external drag resistances, etc. In cases where the locomotives are very closely matched and couplers between consisted locomotives are loose, a slightly modified motor value command signal can be transmitted to the followers in order to keep the couplers tight and sharing load as evenly as possible."

I'm not so sure that Ring "speed matched" the locos in the video. I could be wrong but I imagine that Ring would not have bothered going through that lengthy rigmarole to try and speed match them using the MFLC.

- Tim
Title: Re: MOTOR FULL LOAD CURRENT
Post by: KPack on August 03, 2018, 11:37:45 AM
Thanks for the info there Tim.  That clears up one of the questions that I had regarding the locomotive modules communicating with each other.  Initially I thought the lead locomotive communicated with the controller, and then the controller sent the signal out to the followers.  It looks like that is only one of the paths, and that the locomotive modules communicate directly with one another.  Love it!

-Kevin
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 03, 2018, 11:45:08 AM
Quote
As an example, when the lead locomotive is sent a reference command signal to begin movement, its motor power will increase until static friction is broken, then the motor power will reduce in order to maintain a steady roll.

Confirmed. I saw this on the scope. Anytime you move the throttle off of 0%, even if you only move it a little bit, say to 5%, there is an immediate huge current spike that lasts only milliseconds. Following the spike there is relatively high current that quickly trails off. Reminds you of the lights in the garage when the compressor kicks on.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Tom on August 04, 2018, 10:48:54 AM
Alan,

Thank you for the great picture.  I am assuming that “RECTIFIED FILTERED DCC INSIDE THE MODULE” is, at least roughly, the same as “REGULATED DC ON THE RAILS AND INSIDE THE MODULE.”

Since I have no familiarity with DCC, one last question: is a DCC decoder doing essentially the same thing as a Ring Module (the middle row) for power, in addition to picking up command signals from the rails instead of over the air?
Title: Re: MOTOR FULL LOAD CURRENT
Post by: Alan on August 04, 2018, 10:55:11 AM
Since I have no familiarity with DCC, one last question: is a DCC decoder doing essentially the same thing as a Ring Module (the middle row) for power, in addition to picking up command signals from the rails instead of over the air?

Yes.
Title: Re: MOTOR FULL LOAD CURRENT
Post by: TwinStar on August 26, 2018, 12:56:01 PM
Tim:

Where did you find the patent info? I'm got several Free-mo guys trying to tell me there's no way Ring can have no 'radio interference issues' like Digitrax. I've tried to explain how I've stood next to a Dgitrax duplex user who had lost their signal while my RailPro was running fine.

Title: Re: MOTOR FULL LOAD CURRENT
Post by: G8B4Life on August 27, 2018, 09:12:41 AM
Jacob,

The patent info is available online. If you wish to view it go to http://patft.uspto.gov/netahtml/PTO/srchnum.htm (http://patft.uspto.gov/netahtml/PTO/srchnum.htm) and type in Rings patent number (8807487) into the search field. I never got some parts of the site to work properly but you can read the text part.

Your Free-mo friends are correct in principle, unless I'm gravely mistaken there is no radio device on earth that is completely immune to RFI, it's all down to how well the device is designed and built that determines how susceptible to RFI it is. I don't know about DigiTrax's radio system but I do know Ring employs some good RF design, such as the HC has access to 5 RF "channels". I don't know for sure but I imagine it hops between these "channels" frequently (there is a proper term for this but I forget what that is at this time of night!). There is probably a whole host of other things that TR has designed in well, along with how RP operates in general (ie, direct to LM, not all throttles to a single receiver) that gives RP what appears to be almost RFI immunity under normal circumstances.

- Tim