Spring Rate Calculation

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GooseOrBust
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Spring Rate Calculation

Post by GooseOrBust »

Hello

I posted here several years ago while building my Goose. It was finished and worked well.

I now have a riding car for my RS20 and need new springs, I think.

Several people have offered assistance, and for some reason, I'm struggling.

I calculated the weight of me and the car at 320 pounds and bought 16 20 pound rated springs for the 2 trucks.

The ride is smooth as silk, but the car is tippy. When I sit on the car the springs are compresses about 25%.

How do you calculate spring rate to eliminate the tippy and retain truck flexibility?

Thanks
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Greg_Lewis
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Re: Spring Rate Calculation

Post by Greg_Lewis »

Someone once suggested running stiff springs such that the bolster barely goes down when fully loaded. Then put a round-head screw between the bolster and truck frame so the bolster will have a pivot point when the springs are at the top. I've done this and have no problems. The trucks flex when at the top and they hardly compress when loaded. The ride is fine.


Also, here's an Excel spreadsheet for calculating the deflection of leaf springs. I don't remember where I got it and cannot guarantee it's accuracy, but help yourself:
Spring Datal.xls
(19.5 KiB) Downloaded 381 times
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Bill Shields
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Re: Spring Rate Calculation

Post by Bill Shields »

Greg is correct...riding cars the 'float' on springs are unnerving...best to have them bottom out with people on them and lift / rock as needed to accommodate the track.

none of my riding cars of every scale have any springs on them at all..only pivots between the wheels to allow them to rock and track as needed.

They ride very nicely, do not make anyone seasick, feel quite stable and track nicely.

true...they do not look 'prototype...but what is prototype of 12" scale people hanging over 1/8" scale (or 1/16" scale) riding cars???

it is getting around the track safely that is important.
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rkcarguy
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Re: Spring Rate Calculation

Post by rkcarguy »

I try to run at least twice the spring weight I needed for the calculated weight, based on simply trying out a few different ones on my riding car and then sitting on it. I ended up using 8ea 135# springs on mine. I figure my weight and my riding car is around 450#'s. It seems to keep things stiff enough that it's not tippy yet I'll have the capacity for extra passengers if needed (My riding car is a 68" long hopper).
The only downside is they are a huge pain to get installed, and the freight cars are going to be much worse as I'm building them for 1-ton gross weight each.
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Steggy
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Re: Spring Rate Calculation

Post by Steggy »

I intentionally built my control car for my F-unit so it would be heavy (450 pounds minus engineer and conductor). That way, I could run fairly high rate springs and avoid that tipsy feel, while still maintaining a comfortable ride over roller coaster track. The problem of tipsy cars comes down to the mass of the car being low and low-down and the mass of the riders being high and high-up. That dichotomy can only be handled by making riding cars significantly heavier than their non-riding counterparts.
Greg_Lewis wrote:Also, here's an Excel spreadsheet for calculating the deflection of leaf springs. I don't remember where I got it and cannot guarantee it's accuracy, but help yourself:
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Johnny O
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Re: Spring Rate Calculation

Post by Johnny O »

Take a look on The Golden Gate Live Steamers site. I think I used literature from them on locomotive construction. I remember seeing a section on calculating spring rates in it also.
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Re: Spring Rate Calculation

Post by John Hasler »

Libreoffice can usually open Excel spreadsheets.
Glenn Brooks
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Re: Spring Rate Calculation

Post by Glenn Brooks »

I just went looking for a couple of 185# 2” x 1.75” replacement springs, for an old set of trucks Iam rebuilding. Several, springs had gotten lost along the way.

As FYI, I searched all the usual suspects: Amazon, eBay, and then initially ordered replacements from MSC. Afterwards, realized these were all light duty springs, e.g. in the size, between 45# to 100# load bearing. So way below the rating I needed. These springs were piano wire construction - small diameter and fewer coils.

So went off searching the Internet for heavy duty springs. I found several commercial spring manufacturing companies that offer a variety of heavy duty to super, industrial strength capacity springs. Same dimensions, but with .195” diameter wire and 3 coils to the inch- so 185#+ capacity. They cost twice what the light duty springs cost, but, are high cycle, heavy duty service, equivalent to the others already on hand.

So, what I learned is: wire diameter size, number of coils, compression rates, and material type are critical to ordering the proper style of spring. These are things I had not paid close attention to previously.

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tomc
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Re: Spring Rate Calculation

Post by tomc »

we used chevy valve springs and if we needed a bigger load carrying capacity, we used heavy duty.

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rkcarguy
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Re: Spring Rate Calculation

Post by rkcarguy »

Small Block Chev valve springs work good for larger scales like 2.5" and 3", lots of different rates, and they are sometimes progressive so they will ride nice when your car is empty but stiffen up when loaded down.
rkcarguy
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Re: Spring Rate Calculation

Post by rkcarguy »

X-1 Trucks.jpeg
These are 2.5" X-1 trucks, SBC valve springs if I remember correctly.
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