Electric drive motor specs

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Glenn Brooks
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Re: Electric drive motor specs

Post by Glenn Brooks »

Yep, looked and measured again today. Don’t see a way around the big sprocket requirement without 9” or 10” diameter wheels, or a gear box of some kind. Could use the existing gear box, but that doesn’t solve how to add a second motor on the other truck. Trying to do this in phases, and stay away from multiple rebuilds and sunk costs.

Plus, looked at the motor I brought home yesterday. It’s half the power rating the guy said it was. So back to “Bobs Used Motor” store and see about an upgrade or refund. Oh well, more drawing board time...

On the bright side, I found a terrific outlet for large capacity (1300 amp) 12v batteries at the local NC Cat dealer. These are 1 year old replacement batteries from hospital standby generators. Big Cat engines are all hi amp loading 24v starter systems. So these should be ideal for traction motor requirements. Apparently the bay heroes are replaced every 12 months, on schedule. 24 volts, 2600 amps, $400.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Steggy
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Re: Electric drive motor specs

Post by Steggy »

Glenn Brooks wrote: Thu Oct 29, 2020 9:56 pm Yep, looked and measured again today. Don’t see a way around the big sprocket requirement without 9” or 10” diameter wheels, or a gear box of some kind. Could use the existing gear box, but that doesn’t solve how to add a second motor on the other truck. Trying to do this in phases, and stay away from multiple rebuilds and sunk costs.
I could see doing this with a worm drive, one per axle, with the traction motors mounted longitudinally in the truck frame. Are you up for making a gearbox? It's not too difficult if you have a decent mill and lathe at your disposal.

You would need a four-start, hardened-steel worm and suitable worm gear, iron recommended (bronze, while cheaper, introduces lubrication problems). With a four-start worm, the gear ratio would be N × .25, where N is the number of teeth on the worm gear. For example, to achieve 6:1 reduction, you'd use a 24 tooth worm gear with a four-start worm. Such a gear train is reversible, unlike a single- or two-start worm drive. Suitable parts are available from Browning Power Transmission, Boston Gear and others.
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Glenn Brooks
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Re: Electric drive motor specs

Post by Glenn Brooks »

BDD, indeed my first thought was to make a worm drive. I would be up to making something as you describe. Are the shafts that enter the gear box, typically supported with bearings?

Glenn
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Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
rkcarguy
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Re: Electric drive motor specs

Post by rkcarguy »

Glenn, the "Athearn" HO scale trains come with a setup like that, they use a single electric motor mounted in the center with drive shafts extending out to worm gear boxes on each truck. Yes it's complicated but would let you put a big electric motor in the middle where there is a lot more room instead of being confined to inside or on top of each truck.
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Steggy
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Re: Electric drive motor specs

Post by Steggy »

Glenn Brooks wrote: Fri Oct 30, 2020 6:00 pmBDD, indeed my first thought was to make a worm drive. I would be up to making something as you describe. Are the shafts that enter the gear box, typically supported with bearings?
I'm not sure if I understand your question.
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Glenn Brooks
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Re: Electric drive motor specs

Post by Glenn Brooks »

Wondering about the overall design of a gear box, and how the gears and their shafts are supported inside the casing. I assume a seal around the shaft as it enters and leaves the casing, but would the shaft also be supported by a bearing at the opening to the gear box? Something to hold it in place...?

Glenn
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Steggy
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Re: Electric drive motor specs

Post by Steggy »

rkcarguy wrote: Fri Oct 30, 2020 9:42 pmGlenn, the "Athearn" HO scale trains come with a setup like that, they use a single electric motor mounted in the center with drive shafts extending out to worm gear boxes on each truck. Yes it's complicated but would let you put a big electric motor in the middle where there is a lot more room instead of being confined to inside or on top of each truck.
I was thinking more along the lines of how it was done in PLCC streetcars. The traction motors are mounted longitudinally within the truck frame and transfer power to the axles through a driveshaft fitted with U-joints. Each axle assembly uses spiral bevel gearing to shift the power flow 90 degrees and provide reduction—an arrangement that resembles the rear axle in a rear-wheel-drive automobile.

Glen could do it with spiral bevel gearing (there are sources for the parts), but may run into difficulty achieving sufficient reduction. That is why I proposed using worm gearing. I foresee that the fabrication challenges would be about the same with either gearing type.
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Steggy
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Re: Electric drive motor specs

Post by Steggy »

Glenn Brooks wrote: Sat Oct 31, 2020 1:18 pm Wondering about the overall design of a gear box, and how the gears and their shafts are supported inside the casing. I assume a seal around the shaft as it enters and leaves the casing, but would the shaft also be supported by a bearing at the opening to the gear box? Something to hold it in place...?
Worm gearing generates a combination of radial and axial thrust vectors, which given that your application would run the gearing under load in both directions, are best counteracted with Conrad style ball bearings or opposed tapered roller bearings in a straddle-mounted configuration.

One method would be to make a shaft for the worm that has a bearing on one end that is mounted in a "blind" retainer that is removable—the retainer would fit into a bore in the gearcase. On the other end of the worm would also be a bearing, it too mounted on a removable retainer and equipped with a shaft seal. That end of the shaft would be keyed or splined to accept the drive shaft from the traction motor. The shaft would be machined in varying diameters, such that the surface that mounts the worm is larger in diameter than the bearing and seal surfaces, which would be larger in diameter than the keyed/splined shaft end. Worms in the size range you would need have keyways, which means your shaft would need a matching keyset. I'd be inclined to make the worm a press fit on the shaft.

The worm gear would be supported by the axle and keyed to it. The axle, of course, would require seals at its exit points from the gearcase. Worm gears generate both radial and axial thrust vectors, same as the worm, with the axial thrust being significant.

Another bearing solution would be use of drawn cup needle bearings for radial loads and needle thrust beatings for axial loads. My principle beef with that approach is the bearing surfaces on the shafts would have to be hardened and ground.

Regardless of the bearing type that is chosen, a means must be present to set endplay to a minimum. Tapered roller bearings must be preloaded.
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rkcarguy
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Re: Electric drive motor specs

Post by rkcarguy »

Glenn, you could use sprockets and chain and only one right angle gearbox per truck to keep things simpler and still have all wheels driven.
Surplus center has all that stuff it's fairly inexpensive.
Glenn Brooks
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Re: Electric drive motor spec

Post by Glenn Brooks »

Thanks guys,

I’ve lined up a new right angle gearbox with the correct sized bores for each truck from the local distributor. The one existing truck I am working with already has existing sprockets to drive the second axle. So just need the proper size motor, fab up a motor mount on the truck, and short connection to the gear box/axle. (I want to experiment with one powered truck, then power the second, if the experimental truck performs well enuf. My plan is the second power truck will add additional tractive effort to pull added weight of several passenger cars.)

Thinking I will order the tolomatic with a 2:1 reduction then couple it with some sprocket and chain reduction off the motor to get into the ball park. Then experiment with variable voltage inputs to see how it pulls on the low end of the curve. Should be able to achieve 200 - 300 rpm with around 15-20 volts DC. Even if the top end (36v) would blow the loco off the curves at full speed. That’s my theory anyway.

My biggest problem is proving to be sourcing the components. Only one shop stocks used forklift motors anymore in the Seattle area. Their 24v 6” diameter motor I bought new turned out to be way underpowered, so I took it back. And nothing else turned up, until yesterday. Now finally I’ve been in contact with a local EV club member who has several 8” and 9” salvage forklift drive motors available, that he is willing to give away. Perfect for experimenting with “feeds and speeds” with variable voltage inputs, if they spin over... I’ll find out next Tuesday...

Glenn
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John Hasler
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Re: Electric drive motor specs

Post by John Hasler »

If they don't spin, rebuild them. 9 times out of ten all a DC motor needs is brushes and to have the commutator turned.
Glenn Brooks
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Re: Electric drive motor specs

Post by Glenn Brooks »

Happy New Year everyone. Looks like we all made it to ‘21.

Don’t know what to say about 2020, except “... the witch is dead. Huzzah, Huzzah, Huzzah”. And, thank you for your assistance figuring out Elextromotive power on my old tired yard goats.

This is down time in the shop, due to the necessity of lounging around in the southwestern desert til winter goes away up north. So, decided to get out of the “spa”, and recheck my calcs and confirm the backyard engineering for this ET (electric train) Conversion.

Here’s a summary of the operating envelope I think i can achieve:

train speed: 10 MPH max.
max overall train weight: 10,000#, (30 passengers, riding in 5 rail cars, pulled by a 1500# locomotive)
operating time: 8 -10 hours per day.

Tractive Effort:
total train resistance @ 5 tons gross weight = 310#
locomotive tractive effort @ 1,450# on drivers = 362#
Drive wheel axle torque (6.5” OD drivers) = 1080 inch pounds at 517 RPM (max train speed of 10MPH)

Motive power: Correction- 6.9”(not 8”) series wound, 48v forklift motors, (over clocked to 72v maybe?). One per truck.

After having a number of conservations with EV (electric vehicle conversion) folk, I’ve become confident these smaller 7”, 8”, or 9” series wound DC motors will be a good solution for park gauge scale locomotives.

The key seems to be these motors have an effective range of horsepower that varies according to current input.(thanks John!). For example, they do not have fixed horsepower ratings, such as an ICE. Rather the controller can vary power input, to achieve varying, horsepower outputs to the drivers ; from 0 volts/0HP (stopped, motor not turning) up to 30+ Hp at 96 v input. The key is not rated engine HP, rather axle torque (and traction) delivered to the rail by the motor output and drive train. So Iam more confidant now than before, on building and testing thenyard goat center cab with one 48v (1000 pound inch) drive axle traction motor per truck. This should provide the torque necessary to move the 310# of train resistance resulting from a 10,000 consist. Adding additional weight on drivers (more batteries) can increase tractive effort, as necessary, and extend amp hour reserve for longer operating time.

I’ve been looking into lithium batteries to extend battery life and operating capacity. However, in the case of the yard goat, lead acid batteries are actually a plus. They add the needed weight to the locomotive to achieve the required tractive effort.

I still need to confirm a speed reducer design to operate these motors at the slow, low voltage end of their power curve. The DC motors produce full torque at start up, but I still don’t understand how they function continuously at reduced voltage, say 15-20 volts, without melting down. So,far the gear reducers I’ve found are very expensive - $1000-$3000 each, and don’t seem to be readily available in the 3000-4000 input rpm range.

Also, haven’t found much data about torque or Hp rating. Except most speed reducers I’ve seen are rated for small <2hp motors. I doubt these will hold up to higher torque loads. The EV people don’t worry about this much, as they have already have OEM transmission and rear differentials engineered and mass produced for each make and model of car or truck. So, still sitting here in kind of a black hole.

BDD’s recommendation to make worm gear reducers looks like a good solution. Golf cart rear ends are a possibility (12:1 gear boxes), but I question if they are robust enough for this kind of service. It would be ideal to avoid having to build gear boxes from scratch. More research to be done, I guess. Fortunately my iPad does have connectivity at the pool.


Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
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