Why are worm gear drives the most common?

[tsgtbob]

Got in a discussion at the LHS about locomotive drives. Now, I'm a 2 rail O scaler, so I'm expected to understand the mind of the 3 rail community (why, I don't know) Okay, here's the question on drives. Why are worm gear drives so common? Is it cost, or is there some other reason? Other hobby drives (slotcars for example) use a scaled down pinion and ring gear system similar to automotive drives, or electric R/C flyers that use a gear reduction that allows freewheeling when batteries are discharged? Yes, I remember the old Tyco "powertorque", and no, I don't want to EVER go back to THAT! I have been thinking on this lately, using a pinion system to reduce motor RPM to usable levels at the wheels. I had an HO scaler ask me why O gaugers (and by inferrence O scalers) have to have dual motor drives. The only answer I had was "it goes back to the old Lionel F-3s, they had two motors, so to that market, two motors means quality." Personally, I prefer a single motor drive, (such as an All-Nation or a end tower Weaver), rather than a dual motor. Any comments?

[NeO6874]

I think the biggest reason (for HO) is space.  there's just no room for anything inside the loco after you've added the weight and stuff - so making the motor-to-wheels connection as simple (and small) as possible, you can cram as much weight in the locomotive as possible... as for two motors... I don't know. Maybe in O scale where there is more room to cram in weight (and heavier things in general) the second motor keeps the train "alive" longer - ie each motor is doing only half as much work as compared to a single-motored loco....

[Virginian]

Worm gears give you the biggest possible single stage gear reduction ratio.  At the motor power levels we are at fit is not critical.  Hence, lower cost, less space required.  Slot cars were looking to go fast, model trains are supposed to go slow well.

[Anonymous]

Also remember slotcars were driving one powered axle. Model trains drive 2 or 3 per truck the easiest way to power several axles like that is a worm gear.

[Paul3]

I think the main reason why worm gears are used is that they provide the best tourqe for the size and speed we want for model railroading.

The other, and quite important reason is that with worm drives, we're able to stop our locomotives and therefore our trains on grades.

Some old Key (brass) steam locos had the "coasting" drive, and it was very smooth running.  However, if you ever tried to go downhill, you found yourself at the controls of a runaway, and the only way to stop it was to throw it into reverse and apply power...then it stopped on a dime.

Paul A. Cutler III
*************
Weather Or No Go New Haven
*************

[R. T. POTEET]

tsgtbob, just call me former-tsgtjay!!!

I am not a mechanical genius by any stretch of the imagination but the only other drive system besides a worm/worm gear drive system I can think of is what I will call a differential drive system - and that may very well be the same as your pinion/ring gear drive system.  This drive system was, I have been lead to understand, quite prominent in O-Scale/O-Gauge in the twenties and thirties and perhaps even lasted into the post-WWII era.  There may have even been some use in HO-Scale in the 1930s and into the late forties but I never encountered it in HO-scale.

I did, however, encounter it in O-Scale/O-Gauge.

In the mid-60s I joined an HO club in the Springfield, Mass area.  This club went back into the late-thirties and had, several years before, converted from outside third-rail AC to 2-Rail DC but we had one cantankerous (but likeable) old codger - a WWI veteran well into his sixties if not already into his seventies - in the club whose home layout was still an outside third-rail pike.  He was having to double purchase things - one locomotive for the club and one loco for home and he was genuinely tired of having to convert his newer HO purchases from DC to AC so they would run on his home pike.  So, for about five or six Saturdays in a row, the club descended on his place to relay track and rewire his layout from AC to DC.  He had, until converting to HO in the thirties been an O-Scaler/O-Gauger and I got looking over some of his O-Scale/O-Gauge models from the twenties and thirties and discovered this strange mechanism on the axle of his steamers.  The looked surprisingly like the differential of my '59 Chevy and when I ask about them I was told that that was what they were, differential drives. 

[jeffrey-wimberly]

I remember the drive system that was used on some HO scale locomotives in the 50's and 60's. It was called a rubber-band drive and used exactlt that to turn the wheels. They had NO crawl capability, starting at a slow speed was nearly impossible and they went fantastically fast, so fast they would flip off the track in a 30'' radius curve! I for one, am glad this drive is no longer used.

As for the worm drive, I can think of three good reasons for it's popularity.

1. It gives good control at slow speeds.

2. It's cheap to manufacture.

3. It's ruggedly dependable.

[rrebell]

tsgtbob, just call me former-tsgtjay!!!

I am not a mechanical genius by any stretch of the imagination but the only other drive system besides a worm/worm gear drive system I can think of is what I will call a differential drive system - and that may very well be the same as your pinion/ring gear drive system.  This drive system was, I have been lead to understand, quite prominent in O-Scale/O-Gauge in the twenties and thirties and perhaps even lasted into the post-WWII era.  There may have even been some use in HO-Scale in the 1930s and into the late forties but I never encountered it in HO-scale.

I did, however, encounter it in O-Scale/O-Gauge.

In the mid-60s I joined an HO club in the Springfield, Mass area.  This club went back into the late-thirties and had, several years before, converted from outside third-rail AC to 2-Rail DC but we had one cantankerous (but likeable) old codger - a WWI veteran well into his sixties if not already into his seventies - in the club whose home layout was still an outside third-rail pike.  He was having to double purchase things - one locomotive for the club and one loco for home and he was genuinely tired of having to convert his newer HO purchases from DC to AC so they would run on his home pike.  So, for about five or six Saturdays in a row, the club descended on his place to relay track and rewire his layout from AC to DC.  He had, until converting to HO in the thirties been an O-Scaler/O-Gauger and I got looking over some of his O-Scale/O-Gauge models from the twenties and thirties and discovered this strange mechanism on the axle of his steamers.  The looked surprisingly like the differential of my '59 Chevy and when I ask about them I was told that that was what they were, differential drives. 

I would like to know about running with ac, was it a low votage form or something like that.

[lonewoof]

Unless you mount the motor SIDEWAYS, you'd have to have bevel or helical gears to get power to the axles. And if the motor WAS mounted sideways, the pinions wojuld all be crammed over to one side. Would also have to have more than one set of gears to get down to a reasonable speed. Worm drive seems to eliminate all that, at least in the smaller scales.

 

[johncolley]

Lonewoof is correct! For the most torque transfer/speed reduction at right angles a worm drive is the only way to fly!jc5729

[R. T. POTEET]

rrebell, I can't answer your question with any certainty - I really do not know just exactly what the voltage was on this old outside third rail HO.

I understand that the early HO imported from Europe came in with 6 volt motors and these motors were relatively large.  To get more torque they went to AC motors because AC motors could be designed and built smaller than their DC counterparts.  These locomotives picked up power through a wiper that extended outwards from beneath the locomotive and contacted a rail outside the two running rails.  This outside third rail conducted the AC voltage for use by this locomotive.

Twelve volt AC motors as used by O-Scale would have been much too large for use in HO sized locomotives - as I understand it even 6 volt DC motors were too big to be practical as HO power in those days and it wasn't  until after WWII that DC powered HO began to take a foothold - motors had, by this time, shrunk in size making DC practical for HO.  I am, therefore, going to surmise that 6 volts was the standard for outside third rail AC.

This was the only time I ever encountered an outside third rail HO layout - and I never saw this one run.  My military duties at the time kept me from going out the first two weekends that the club was helping this guy rewire and retrack his layout - by the time I got out there on the third Saturday most of his outside third rail trackwork had been torn up.