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Re: Ed, that is my experience,with the physics of choo-choo's as well.
Author: Chris Walker
Date: 01-23-2018 - 20:12
Zarkoff wrote:
Synopsis of findings: when wheel is rolling on a rail, the friction between the two is static frcition. When the wheel's surface is moving with respect to the rail, this is dynamic friction. The G-W tests plainly demontrated that dynamic friction can be as little as 50% of static friction, which translates to "less stopping power" no matter how you look at it.
If by reversing the motors, it causes one set of wheels in a pair of motors to spin, which is virtually always the case, then the maximum stopping power of the two axles has been reduced by about 75%.
With EMD DC-drive electrical systems, to reverse the motors, all you have to do is move the reverse lever in the control stand, and the motors will slug (BTDT too). Subsequently opening the throttle will try to drive both motors backwards, increasing the possibilites of a TM flashover, and this will trip the ground relay. As Hot Water has mentioned, once the ground relay trips, the abilities of the TMs to engage any sort of braking vanishes.
My one and only "reversed EMD" experience was while I was still a Fireman, the tired Enginedriver pulled the reverser back into reverse in the dark while running at 25mph, thinking he was pulling the selector knob sand going into DB.
Result to the '63 built G-12 was fused contactors and the unit needed a tow, since it was going nowhere. Nice flashover too!
Chris
in New Zealand
Synopsis of findings: when wheel is rolling on a rail, the friction between the two is static frcition. When the wheel's surface is moving with respect to the rail, this is dynamic friction. The G-W tests plainly demontrated that dynamic friction can be as little as 50% of static friction, which translates to "less stopping power" no matter how you look at it.
If by reversing the motors, it causes one set of wheels in a pair of motors to spin, which is virtually always the case, then the maximum stopping power of the two axles has been reduced by about 75%.
With EMD DC-drive electrical systems, to reverse the motors, all you have to do is move the reverse lever in the control stand, and the motors will slug (BTDT too). Subsequently opening the throttle will try to drive both motors backwards, increasing the possibilites of a TM flashover, and this will trip the ground relay. As Hot Water has mentioned, once the ground relay trips, the abilities of the TMs to engage any sort of braking vanishes.
My one and only "reversed EMD" experience was while I was still a Fireman, the tired Enginedriver pulled the reverser back into reverse in the dark while running at 25mph, thinking he was pulling the selector knob sand going into DB.
Result to the '63 built G-12 was fused contactors and the unit needed a tow, since it was going nowhere. Nice flashover too!
Chris
in New Zealand
