Improving Low Speed Aristocraft & USA Trains
QSI Aristo Decoder
QSI Magnum Decoder
Users have reported that QSI decoders may exhibit some low speed oscillations when running BEMF on certain locos. These locos are usually high current dual motor or large Pittman motors with "loose" gear-trains. This problem appears as a "chatter" in very slow speed running. In addition, sometimes the loco may surge. This usually occurs at DCC speed steps under 15 of 128.
To solve the low speed “chatter”, see CVs 56.18. This CV provides for (4) distinct speed ranges where all 3 motor control parameters (Proportional, Integra, Differential Gains) or “PIDs” can be set.
QSI recommends setting all 4 ranges as shown below specifically for Aristocraft and USA Trains locomotives respectively.
The PID CVs can be set using the Quantum Engineer, any modern DCC system or the Quantum Programmer.
For USA Trains Locos
P I D
6 2 13
6 2 13
6 2 13
6 2 13
| CV56.18.0 | Very Low Speed Proportional Gain | 6 |
| CV56.18.1 | Very Low Speed Integral Gain | 2 |
| CV56.18.2 | Very Low Speed Differential Gain | 13 |
| CV56.19.0 | Low Speed Proportional Gain | 6 |
| CV56.19.1 | Low Speed Integral Gain | 2 |
| CV56.19.2 | Low Speed Differential Gain | 13 |
| CV56.20.0 | Medium Speed Proportional Gain | 6 |
| CV56.20.1 | Medium Speed Integral Gain | 2 |
| CV56.20.2 | Medium Speed Differential Gain | 13 |
| CV56.21.0 | High Speed Proportional Gain | 6 |
| CV56.21.1 | High Speed Integral Gain | 2 |
| CV56.21.2 | High Speed Differential Gain | 13 |
For Aristo-Craft Locos
P I D
10 2 5
10 2 5
10 2 5
10 2 5
| CV56.18.0 | Very Low Speed Proportional Gain | 10 |
| CV56.18.1 | Very Low Speed Integral Gain | 2 |
| CV56.18.2 | Very Low Speed Differential Gain | 5 |
| CV56.19.0 | Low Speed Proportional Gain | 10 |
| CV56.19.1 | Low Speed Integral Gain | 2 |
| CV56.19.2 | Low Speed Differential Gain | 5 |
| CV56.20.0 | Medium Speed Proportional Gain | 10 |
| CV56.20.1 | Medium Speed Integral Gain | 2 |
| CV56.20.2 | Medium Speed Differential Gain | 5 |
| CV56.21.0 | High Speed Proportional Gain | 10 |
| CV56.21.1 | High Speed Integral Gain | 2 |
| CV56.21.2 | High Speed Differential Gain | 5 |
- Set the Minimum BEMF to 7 for both USA and Aristocraft. This should give you a minimum speed of about 0 .4 to 0.5 scale mph.
- You can set the minimum BEMF higher to get smoother performance if needed. Just for reference, most HO decoders are set at 1.5 scale mph.
- Make sure you set CV2, Start voltage low enough that you get minimum speed; otherwise this can cause some odd low speed behavior.
