Tram Weight to Gradient Ratio

DafyddElvy

1:22.5 & 15mm Scale Trams, , NG Steam Railways
10 Feb 2021
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West Lothian
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Scotland
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A question that came to mind relating to 7mm scale modelling but equally applicable in our scale.

While I appreciate their are a lot of variables when it comes to motorising our model trams, is anyone aware of an optimum weight to power ratio for a 4 wheel car?

A friend and I are at the very stages of planning a new layout which will have one particularly steep grade with a curve at the top of the gradient, and we are looking for guidance on the maximum weight to make our models which will predominantly be 4 wheel with both axles powered, any suggestions appreciated, thanks.
 

dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
25 Oct 2009
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St.Neots Cambridgeshire UK
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A question that came to mind relating to 7mm scale modelling but equally applicable in our scale.

While I appreciate their are a lot of variables when it comes to motorising our model trams, is anyone aware of an optimum weight to power ratio for a 4 wheel car?

A friend and I are at the very stages of planning a new layout which will have one particularly steep grade with a curve at the top of the gradient, and we are looking for guidance on the maximum weight to make our models which will predominantly be 4 wheel with both axles powered, any suggestions appreciated, thanks.
This really is as long as a piece of string. You do not state gradient or curve radius so tricky to reply. But in our scale an LGB tram will manage a 1:20 grade with ease on LGB R1 curves. I would therefore look to a 4 wheel tram to have a similar weight profile. But the you come to motor options, a 2 axle tram with 2 motors may do better, but the you get into steeper gradients how steep would you want to go? See possibly more questions than answers just now.
 

JimmyB

Semi-Retired; more time for trains.
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Traction, weight, gradient, so what is the stall on your motor, I have seen videos about locos up gradients, and a lot depends on the stall amps of the motor. I have 1:25 (4%) on a R2 curve, and to get some of my none traction tyre locos up this with a few items of stock behind I needed to add weight, my Otto is 2.2 kg and now has plenty of traction without stalling. My Bachmann tram (original motor) is now 1.3 kg and again pulls well. How did I get to these weights, set up a test track and add weight in a bag till you are happy with the performance, if you know the stall amperage of the motor, and can add an ammeter all the better.
 

Rhinochugger

Retired Oik
27 Oct 2009
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In G Scale, if you move away from proprietary chassis, and are thinking of kit-built or scratch-built mechanisms, the weakest point tends to be the drive gear. Therefore, irrespective of any stall characteristics of the motor, the gearbox or drive mechanism is the area to concentrate on.

Gear ratio plays an important part, and for trams, that could easily be 50:1 or even lower (i.e. 60:1) and for fairly light vehicles, 3D printed gearboxes with brass bearings could well work.
 

JimmyB

Semi-Retired; more time for trains.
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In G Scale, if you move away from proprietary chassis, and are thinking of kit-built or scratch-built mechanisms, the weakest point tends to be the drive gear. Therefore, irrespective of any stall characteristics of the motor, the gearbox or drive mechanism is the area to concentrate on.

Gear ratio plays an important part, and for trams, that could easily be 50:1 or even lower (i.e. 60:1) and for fairly light vehicles, 3D printed gearboxes with brass bearings could well work.
My OcCre Streetcar has a 3D gearbox and brass gears, however I have had to add 1kg weight to get any traction
 

JimmyB

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Wow, that sounds like a lot of weight, sorry, should know this, but are the axles sprung? I assume both axles driven.

Greg
Not sprung as such but with lateral movement, however only 1 axle is driven, but I may have to consider powering another axle
 

JimmyB

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Yeah, I would worry a bit with just one axle driven, I thought I saw some posts where someone had powered both axles. That sure seems a lot of extra weight on a single tram.

Greg
It is not a tram but a two bogie SF streetcar, quite a different beast.
 

JimmyB

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Same principle applies though.
Not totally, 2 bogies vs 1 pair of fixed axles, plus this is the size of my 10-wheeler (minus tender), and is actually lighter than that at a total weight of 2Kg, there will be more of this in my Streetcar thread.
 

dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
25 Oct 2009
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Seams to me that there is collective forgetful ness about Delrin Gear Dives. Though if you do not know about them, well you don't know what you don't know, So long as you get the right axle fit (though you can drill them for larger axles) they work very well indeed. Instantly adaptable to differing wheelbase length with extra chain. I have been using them for a while now with complete success. Here are a couple of my uses on an 0 gauge Hymec and G Steam Tram. Ok both use Swift 16 Chassis but I have used them on IP Chassis and Scratch Built ones and would have no hesitation using them for Gauge 3 that I dabble with. C63E69C8-2F74-4B43-88FA-C19B87F35963.jpeg