Question about an old-style Rivarossi Big Boy

Discussion in 'HO Scale Model Trains' started by Spawn of Chaos, Jan 16, 2007.


Two motors a good idea?

  1. Yeah, the power offsets the weight.

    1 vote(s)
  2. Nah, the weight would make it run worse.

    0 vote(s)
  1. Would it be a good idea to have it remotored with a separate motor for each set of drive wheels? Added power vs. added weight...

    Tell me what you think!
  2. LongIslandTom

    LongIslandTom Member

    Remember the pulling power of the locomotive is a balance between motor torque and the weight... Too much motor torque but not enough weight means you are going to get a lot of wheel slip, which means the locomotive can't pull very much. Too much weight but too little motor torque means the motor might get stalled, which might cause the motor to burn out (or fry the DCC decoder if the loco has one).

    Also, multiple motors means more noise, plus the constant tug-of-war between the motors might result in jerky running. DCC decoders also have a limit in how much amperage it can supply, and if motors draw too much power, you will burn out the decoder.

    You want to minimize the number of motors and maximize the weight, at the same time making sure the DCC decoder can provide adequate amperage to the motor(s).

    Hope this helps.
  3. Russ Bellinis

    Russ Bellinis Active Member

    A better solution than 2 motors would be a single can motor with 2 shafts, one at each end, driving 2 separate gear boxes to the 2 sets of drivers. I don't know if that sort of conversion is possible with the old Rivarossi Big Boys.
  4. Aaaaand...neither of you noticed the poll.

    I'm just looking for opinions.

    The loco is NOT dcc nor will it ever be! I don't care about all that, I just want to see it running!
  5. LongIslandTom

    LongIslandTom Member

    I did see the poll... Which I don't think is of much use actually, which is why I took the time to explain the balance required between weight and torque.

    If the loco is not DCC, the relationship between weight and torque still applies. DCC simply adds another parameter, and that is the maximum current draw the decoder can handle (in amperes).

    Hope this helps.
  6. Yeah...I was thinking of slapping a bigger motor in, and then I had an idea: Put two in! Double the power, with enough weight to keep it in ratio I think.

    I was also going to make all the drive wheels drive...good idea bad idea?
  7. Dragon

    Dragon Member

    If the Big Boy is like my old Rivarossi mallet, then all drivers ARE drive wheels. The motor drive the third driver set on each engine via gearing, and the side rods transmit that power to the other drivers.
    I've seen older brass triplex locos that have a motor for EACH engine...that means three motors for one locomotive.
    you can run two, and it WILL drastically increase the pulling power (as long as there is sufficient weight to hold traction). But even with two identical motors, there is a chance that they will be out-of-sync. That will give you prototypical wheelslip on one engine vs. the other.

    Also, don't the older Rivarossi have traction tires on the third or fourth drivers?

    I can't say if using two motors is a good or bad idea, but if it helps, I plan on remotoring my kit-bashed Y6b triplex (2-8-8-8-8) using one motor for the loco and one for the tender.
  8. Russ Bellinis

    Russ Bellinis Active Member

    Bachmann used two motors for the original GE 44 tonner that they came out with in the spectrum line. They were very bad runners because the motors weren't always compatible. They just couldn't be synchronized. The solution for the Bachmann was to wire the 2 motors in series unstead of parrallel. The thing to keep in mind, if you have room for two motors in the shell, will it pull better with 2 motors, or with one motor and extra weight? The second motor will take up space, and will weigh a lot less than the same volumn of lead.
  9. Umm...that's nice.

    Anyways, no, the Rivarossi Big Boy that I have only has two drive wheels powered on each set of eight (which I also plan on changing sign1).

    I do believe that I can add power and still keep the weight in ratio to that power so it'll work right; atm it's really weak, but that's just cause it needs oiling (it runs at like 25% speed at 100% power :curse:).
  10. msowsun

    msowsun Member

    "Spawn Of Chaos"............. Is your Big Boy like the one in the diagram below? Does it have the original squared off motor? Or a rounded off motor that came out later? The lastest versions have the motor enclosed in the boiler and is not visible in the cab. In any case, ALL big boys have ALL drivers powered, but like Dragon said, the power is transfered to all the wheels by the side rods just like a real loco. If your side rods are missing then you WOULD only have 2 wheels powered and it would run like crap.

    I bought a used Rivarossi Big Boy in 1986 for $75. It ran OK but was a little noisy. I decided to remotor it and went with 2 Mashima can motors. They were installed roughly in the positions as below in the diagram. I used rubber tubing to act as universals to connect the motor shafts directly to the worm gear shafts because the shafts did not line up exactly.

    The extra power of the extra motor really wasn't worth it because it did not pull any more than before. Even 1 motor had enough power to spin all 8 wheels. Once you spin the wheels, you have lost traction. Only weight will improve traction.

    I am glad I did it though, because when pulling a heavy load, you could sometimes get one set of drivers to spin before the other set. This could happen from a start, or even when in motion. .....Very Cool...... :thumb: I sold it about 10 years later for $100.

  11. Yeah, same one. However...I looked at the gearing, and only one pair of drive wheels is geared on each drivetrain.

    I might add some lead weight if it proves to be too powerful for the weight; it's just for fun anyways.
  12. pgandw

    pgandw Active Member

    On steam engines, only gearing one axle is normal in HO. The remaining drivers are driven by the side rods. The prototype is the same way. The cylinders push the drive rods, which is attached to the main driver set. The side rods cause the rest of the drivers to turn at the same time as the main driver.

    An articulated engine (like a Big Boy) has 2 separate steam engines, each with its own set of cylinders, drive rods, and side rods. On the prototype, the front engine is hinged at the rear to enable a large steam locomotive to go around sharper curves. Model articulated locos generally let both engines pivot near the middle of each to permit much sharper curves than the prototype.

    Diesels and geared steam locomotives generally do not have side rods to transmit the power so the better models are geared to all axles.

    On any model, if the drive wheels start spinning before the motor has reached its maximum current rating, you can add more weight to get more traction. If the motor has not reached its max current, adding a second motor serves no purpose. On the other hand, if the motor reaches its max current before the drive wheels slip, then a larger or second motor is needed to take advantage of the existing traction. A single larger motor usually makes for a smoother running loco than 2 smaller motors. The only advantage of 2 motors on an articulated is being able to see each engine slip its drivers independently (like the prototype). I don't have track long enough to put enough cars to get into this situation, so it doesn't matter much to me.

    As far as what other people's opinions are (the poll), who cares? You want conclusions based on experiences and facts, not opinions (IMHO :) !).

    my thoughts, your choices
  13. Good point on the poll I guess. I'm still going to go for the double motor cause it'll probably have enough weight not to slip before it reaches max current; I'm going to oil it and run it as is for a while to see how well it works.

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