Detailed Explanation of Upgrade; BEMF and Regulated Throttle Control Features
QSI- BEMF
Message: 20
Date: Tue, 28 Feb 2006 01:35:04 -0000
From: "g_pruss"
Subject: BEMF in QSI equipped locomotives
There seems to be some confusion in regards to the use of BEMF in QSI equipped locomotives. Hopefully I can clarify the matter in this note.
All QSI equipped HO locomotives use BEMF voltage to measure the speed of the locomotive. One or more pre-production models of each of these locomotives are calibrated at QSI to map the BEMF voltage to scale MPH.
The BEMF to SMPH mapping is used in a variety of ways in all locomotives, including:
(1) To determine the amount of doppler shift.
(2) To determine whether the locomotive is quickly decelerating so that the brake squeal should be played.
(3) To determine that the locomotive is moving or stopped.
BEMF is also used to determine the chuff rate in steam locomotives.
All the above uses of BEMF are present in all QSI equipped HO locomotives and have never been disabled.
What has been "disabled" is the use of BEMF to try to maintain a constant locomotive speed. QSI equipped models which support Calibrated Speed Control try to maintain the BEMF which maps to the SMPH corresponding to the DCC throttle speed step. For example, if the throttle setting were at 10 the locomotive would attempt to maintain a BEMF which maps to 10 SMPH. It is this Calibrated Speed Control feature which has been "disabled".
The legal issue does not really have anything to do with BEMF. It is the Calibrated Speed Control. It does not matter if BEMF or a optical or mechanical cam is used to measure the speed. The legal issue is maintaining a constant speed based on a throttle position communicated digitally to the locomotive.
As far as you model owners are concerned, the Calibrated Speed Control feature has been REMOVED from the firmware. QSI deliberated whether or not to keep this feature in the firmware in a disabled state to be enabled later by some mechanism, but our lawyers advised against this. If one of you clever guys actually discovered the enabling mechanism and posted the mechanism on the internet, then it would be as if we had not disabled the feature in the first place.
From my point of view as a software developer, the Calibrated Speed Control feature is DISABLED. The feature exists in the source code for the firmware and I can enable/disable it at will for each firmware build by defining/not defining a compiler flag. When the compiler flag is not defined, the source code for the feature is skipped by the compiler and the executable code for the feature does not exist in the resulting firmware module.
It is often hard to communicate subtle distinctions such as the difference between "disabled at compile time" and "removed from the firmware", but hopefully you can see the difference.
Will future QSI equipped locomotives include Calibrated Speed Control? I am told not until the legal issues are settled.
However, the issue of Calibrated Speed Control is becoming less and less important to QSI. We believe we have a much more prototypical control mechanism in Regulated Throttle Control (RTC). Calibrated Speed Control is roughly equivalent to automobile Cruise Control, where the automobile attempts to maintain a constant speed up hill and down hill, regardless of load.
Do any modern Diesel or Electric prototypes have Cruise Control?
RTC operating under Analog DC has been available in all version 6
firmware modules.
With the Quantum Upgrade Program, RTC operating under DCC will also
be available.
Gerry Pruss
QSI
