That would be great if you could generate the mappings for the motors under the load!
The easiest way to model dynamic load would be to drive one or a couple of disconnected 393 motors with your test motor. If you have an access to 5W 10-50 ohm resistors you can use them as an easy way to adjust the test load by connecting to the wires of the slave motor.
As you run the tests you may want to monitor the battery voltage. I would plug an external voltmeter into the adjacent motor port, because there were reported issues using nImmediateBatteryLevel.
The best voltage to conduct the tests would be around 7.5v when the battery is slightly discharged and chugging along the long, almost flat, slope in the middle:
Also, you may want to report the load in RPM drop from the idle speed at the same motor control power (or the percentage of the expected max idle speed).
Ideally, you would be able to come up with a set of mappings for 0%, 5%, 10%, 15%, … loads and a function that could interpolate between them when necessary.
The more load there is, the flatter the curve should become. Here is a graph from NbN season that I just posted in another thread:
X-Axis and column B is the desired RPM of the turbo motor under load (max idle angular velocity is expected to be 240 RPM)
Y-values for the blue line and column C is the motor control level that was necessary to achieve that velocity when motors are connected through MC29s. Red line and column D corresponds to ports 1 and 10 and column F is the ratio between the two.
As you can see at about 20% load, our test data shows almost linear dependency between motor control level and output speed in the region between 100 and 190 RPM.
20% or even higher momentary loads are ok, but for the best motor performance you, probably, want to keep the motors operating at 10%-15% load levels. That would be 90-85RPM for the speed or 1.5-2.5 for the output torque on the graph:
The above graph assumes nominal speed of 100 RPM and 10% load would be 10 RPM drop to 90. If you were commanding motors to run at 50 RPM when idle and then added similar load (same resistive torque) it would still result in the drop of approx 10 RPM (because delta RPM corresponds to delta voltage and therefore effective current and output torque). To avoid confusion I would count that 10 RPM drop as 10% load, compared to max idle 100 RPM velocity, and not vs commanded 50 RPM or actual 40 RPM.