It’s my understanding that most (perhaps all) DCC systems allow for setting a train to a constant speed, regardless of grade, etc. If that’s correct, what happens when a loco develops wheel spin on a grade? Does the DCC act sort of like traction control on modern autos and slow the wheels down? If so, would this actually improve the tractive effect of the loco?
I believe what you are referring to is Back EMF. It should match the motor speed to the throttle setting regardless of wheel traction. As long as you have traction it would increase the power to maintain the motor speed or reduce the power to maintain the motor speed regardless of traction. The link is to the explanation of Back EMF on the Digitrax site.
Thanks Tachyon. Very helpful info.
All my engines have the BEMF decoders and when they encounter a grade that the engine has trouble making it to the top the engine wheels are just slipping as they would normally and usually the engine just keeps grinding up hill until it is able to regain traction again.
I never really see any speed jerking as the engine regains traction and begins moving faster as the BEMF is so smooth in its action.
Others on different forums have reported seeing jumps in speed at times but I feel that this is caused by not having the decoder BEMF settings adjusted properly. I don’t know why there are so many modelers afraid to make changes to the CV settings to correct these minor problems but just expect the decoder to work great right out of the package.
I always thought that is the reason the MFG put the CVs there to fine tune the decoder to each individual engine.
Just my thoughts and a happy DCC owner.
BOB H - Clarion, PA
I have only one with BEMF, a Lionel HO Challenger. The others, all BLI locos, will spin if they get overloaded, but their rate of chuff and wheel rotation remain at the point where slippage began. Most often, unless the benevolent hand of the Great White Chieftain assists, it will not regain its footing. I would like to think that it is a testament to my superb track, but I am not so naive…nor so arrogant. Instead, the loco does what it can under the circumstances, and will need help when the time comes. Once over the tough spot, which regrettably is an indication that my track is not perfect, it regains its footing and continues apace.
I believe that most decoders have a CV that controls load compensation. For certain, my lone FA2/B2 combo with a cheap 100LC, and my steamers all increase work sounds when I make them strain using a throttle input. Setting CV 3 slows their acceleration, but the decoder will continue with the labouring sounds until the train speed matches the decoder’s throttle setting.
Just in case you haven’t figured it out from the previous answers, this is a function of the particular engine decoders, not the DCC control system. Some decoders, like the QSI upgrade chips, and Tsunami, among others, have an optional feature called Regulated Throttle Control, which keeps an engine running at a constant speed when running slowly, especially through turnouts or other rough trackwork, but slow down and speed up gradually when going down/up hills, etc. Some even vary the sound when the engine is “laboring”.
Alot of the “Older” BLI’s probably does not have back EMF activated thanks to a lawsuit.
Wheelspin means the load is too great on the engine for the hill.
Thanks, Pondini. That’s very helpful.
The first BLI 4-6-4’s had Back EMF, it was after they first came out that the lawsuit happened. Later versions don’t have it. Digitrax decoders have offered BEMF for quite a while now.
I guess the key point is, BEMF doesn’t increase the engine’s pulling power or capacity. If an engine can’t pull the train up the grade and starts spinning it’s wheels, it’s going to sit and spin whether it’s DC or DCC powered.
BEMF is part of electric motors since the day they were created.
To actually USE BEMF was something that started with that BLI Hudson Sir unless the famous Lawsuit said that someone else tried to patent that part of electric motors. Kinda like trying to bill me for the air I breath today in addition to the electricity and gas for the house.
Now that I explained the great encompassing ignorance in my little brain to the world, I’ll get some coffee and take a nap for a while folks.
It is true that BEMF is part of all dc motors, it is still the decoder that must be designed to make use of the motors’ BEMF.
Unless you use a decoder that has a BEMF feature your loco speed will be at the mercy of grades for its speed (discounting wheel slippage).
BEMF in DCC was applied a lot longer than that. ZIMO started using it in 1980, over 25 years ago! Regards, Art ZIMO Agency of North America www.mrsonline.net
Well actually Back EMF was used to control the spin of motors and turbines a century ago !! It’s just their use in DCC on model railroads that’s relatively new. When BLI produced their first run of Hudsons, MTH sued them claiming the electronics used to harness BEMF was copied from an MTH design (used in three rail trains they produced, I assume). After that initial run, BLI stopped putting BEMF into their engines, but made it possible to be added later if the lawsuit was successfully resolved.
I don’t have much to add, but found this interesting link (Tony’s site is great… ) so here you go…
http://www.tonystrains.com/technews/introto_bemf_pid.htm
Brian