I have been looking at a variety of low cost sources for repowering motors, such as the several electronics discount websites, American Science and Surplus, etc. lately. Is there a preferred rpm range for motors when considering them for repowering projects? What levels of rpm should be avoided? Cedarwoodron
Avoid high RPMs - go for the lowest ones. Most cheap motors run way too fast, and have too little torque. If possible, get ones with neodymium magnets, as they will have a lower current draw that ones with more conventional magnets.
Those are general rules, but it really can depend more on the gear ratio of the engine being powered, if you want to match the scale speed to the prototype speed. Lots of calculations there, of course - since most of our stuff runs too fast anyway, and we don’t really have the room to really crank our fast locos up to the prototype speeds and hold them there without going dizzy trying to watch 'em, make 'em slower.
The motor RPM really depends on your project. For HO scale, the usual preferred range is 8 to 10,000RPM. Engines requiring very small motors usually have a slower gear ratio, because small motors tend to run between 12 and 17,000RPM. You also need to consider torque. A heavy engine usually needs a motor with more power. Very cheap toy motors probably won’t have enough torque to move anything.
What are you looking to remotor exactly?
Generally older Athearn BB diesels, such as GP-9’s etc. that I have picked up at flea markets over the past several years. The point is I am trying to be frugal- if there are some feasible inexpensive motors available thru web sources such as I mentioned in the original post, then my purpose is achieved. If, however, I am buying a pig in a poke, so to speak, then should I stick with the more expensive alternative of NWSL and A-line,etc.??? Darth, I have followed your projects on you tube and here and trust your advice. Cedarwoodron
Athearns are pretty easy when it comes to remotoring. One brand cudaken reminded me of not long ago is Helix Humper. They have “Econo Kits” that reuse the Athearn flywheels and couplings, and at $21, they’re one of the cheapest new options. They require that you do a little grinding of the frame, so they’re not the easiest in the world to use, but the motors run smooth and quiet.
If it’s the old gray Athearn motors you’re replacing, you can also find newer gold motors on eBay frequently. In my experience, they don’t run as well as any good can motors, but they still work better than the old ones.
Those surplus stores often have good deals on motors, but they’re usually single shaft or too large for use in HO scale. You can search eBay for other options, but it’s hard to find good dual-shaft motors for less than $10. And since Athearn’s shafts are 1/8", most motors will need shaft size adapters or new flywheels, or you can replace the Athearn couplings with new ones from NWSL (488-6 for motors with 2mm shaft, 484-6 for 2.4mm shaft).
The RPM advertised on small motors sold separately as just motors, is the UNLOADED rpm achieved when running on rated voltage. All such motors will run much slower under load. Even just the load of the gears will drop the speed a lot, perhaps 50%. The unloaded speed doesn’t tell us very much about how well the motor will function in a locomotive.
For small permanent magnet motors, running unloaded, the rpm tops out when bearing and brush friction equal motor torque. The motor’s torque falls off as speed increases because the motor generates a higher back EMF which opposes the driving voltage and reduces armature current. Torque is directly proportional to armature current. A high unloaded rpm indicates either lower friction or more torque, both of which good things to have in model locomotive service. The major reason motor makers quote motor rpm is because it is easy to measure.
Any permanent magnet motor small enough to fit inside a model locomotive has the potential to be a very good motor. The potential is high enough to make it worth while going to the trouble of fitting the motor into the model. Odds are, it will work just fine. And, lacking fancy test equipment that none of us have, there is no good way to predict motor performance after installation. You just to try it and see.
If a motor is losing 50% speed with no more than the gears, something is very, very wrong. Typically, a motor should lose no more than about 5% of its RPM when running an engine alone, and maybe 10% when an especially small motor is required. With a heavy load of freight cars, it shouldn’t drop more than about 15%. 20% max. If it’s running constantly with a 50% drop, it will burn out in no time.
About the only exception I know of is the old toy train motors. They do lose a lot of speed when running under load, but they’re made to handle that kind of stress. HO scale can motors are more sensitive, and require a free running, high torque mechanism if you want them to last.
Some of the trucks at work use a motor driven gear drive actuator for the HVAC doors. I replaced one one day because of a stripped out gear. I ended up taking it apart. I found a small can motor that measured 1.25 long X .75 inch round. It had an 1/8 inch shaft with a plastic worm gear. I could not test the RPM but this little motor had a load of torque. I swapped out the motor in my old Bowser I1sa with it. Even though there is no flywheel it runs real smooth and draws less than .05 amp stalled. Making a mounting bracket was the hard part. With a good decoder that has BEMF this became one of my best running locos.
Finding little devices like these are a great source of parts for our hobby.
Pete
I agree, something is wrong for sure. For a motor to build RPM it needs torque. When looking for replacement motor stay around the 15 to 20 thousand RPM range with a torque figure of at least 1 oz/in. The torque number is important or you will just end up with a junk loco. Try NWSL motors, they produce some great replacements. Stay away from the junk stuff. Sure they will spin at whatever RPM they are rated for but without torque they are nothing.
Many thanks to you guys for your feedback. The cheap, cheap stuff is intriguing, but with your info, at least I have a better idea of what to look for. The e-bay route is one I have not done a lot of research on, but there is another avenue to explore. I just wish that this stuff was more directly available locally,at swap meets, but there are a lot of mystery locomotives to be found at those venues-I know, I have bought a number of them! Cedarwoodron