Fine tuning locomotive operation
The factory settings normally provide good performance for most locomotives in H O-Scale. You
may want to improve or fine tune performance by adjust the starting characteristics or top speed .
There are 6 CVs that define:
➙
The voltage at which the motor starts
➙
How often and how hard the motor gets kicked a slow speeds to keep it turning smoothly.
➙
The maximum motor speed
➙
The mid speed range response characteristics or ‘speed curve’.
➙
Compensation for a motor that runs faster in one direction
Start Voltage - CV2 (Vstart):
This is the amount of voltage sent to the motor when first starting up. We set CV2 so the
locomotive is
almost
able
to maintain movement at speed step 1. We then use CV116 and 117 to
apply enough torque compensation to keep it turning on speed step 1. Typical values for CV2 are
in the range of 0-35.
Torque compensation kick rate - CV116:
How
frequently
the motor is ‘kicked’ at slow speed. Typical adjustment is 2 to 4. The smaller the
number the more often the motor gets a brief v oltage ‘kick’. Factory default is 0 (off). A value of 1
applies kicks continuously. The maximum practical value is about 6.
Torque compensation kick strength - CV117:
How
hard
the motor is ‘kicked’ at slow speed. Typical adjustment is 4 to 25 The larger the number
the more voltage is applied in each ‘kick’. The strength of these kicks fade out ratiometrically as
speed is increased providing a smooth transition to normal motor operation. Factory default is 0
(off), usable range 0-50.
Vmax - CV5:
If your locomotive runs too fast you can use CV5 to lower its maximum speed.
Setting CV5 to 255 uses the maximum possible voltage to run the motor when full speed is
requested. Set CV5 to a smaller value to reduce the top speed. A value of 128 will yield
approximately ½ full voltage to the motor at top speed. 192 will provide about ¾ full voltage. All
speeds from the middle speed step to the maximum will be proportionally reduced (see diagram). If
CV5 is set to 0 the decoder will use 255 for maximum speed. Always make sure CV5 is greater
than CV6 to avoid erratic operation.
Vmid - CV6:
CV6 determines how the motor responds through its middle speed ranges to
advancement of the throttle. If you set CV6 lower than half the maximum speed you’ll have smaller
increases in motor speed through the lower speed ranges. Then, as you hit the upper speed
ranges there will be larger increases between speed steps. In the diagram below you can see this
best illustrated by the ‘customized’ line. If you set Vstart larger than 0 you’ll will most likely want to
raise Vmid so a reasonable slope is maintained in the ‘speed curve’. If CV6 is set to 0 the decoder
will use 127 as the value. If you use high values in CV117 you will want to increase CV6 by a
proportional amount to keep a smooth acceleration curve.
Reverse trim (also forward trim) - CV95:
Values from 1-127 make decoder run
faster in reverse
than forward. 1 is one speed step faster in
reverse, 2 is two steps faster, etc.
Values from 129-255 make decoder r un
faster in forward
than reverse. 129 is one speed step
faster in forward, 130 is 2 speed steps faster, etc. 0 and 128 add nothing to either direction .
255
000
064
192
128
1
128
64
32
96
Vmid
Vmax
Vstart
factory default
customized
Motor 'Speed Curve'
Speed steps
Vol
tage
**Last revised: 17 November 2003
Page 3
D15SR
