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Testing Methodology

Utilizing an in-house dyno, CTR Electronics empirically tests motor performance both during our iterative product development process, and also to ensure quality assurance during the pre-production and manufacturing phases of a project.

Our process has been peer reviewed by "motor experts" from both inside the FRC community as well as industry. This same process has been used successfully on several past motor design projects for FRC and OEM customers. In addition we validated our methodologies against existing motors with known "real-world" performance data.

Test Equipment

  • Torque Sensor (accuracy to <1%, up to date calibration)
  • Velocity Sensor (accuracy to <1%)
  • 12V regulated power supply with sense leads for the motor under test
  • Supply side ammeter
  • Supply side voltmeter
  • Braking motor system (provides controlled braking torque)
  • Isolated power source for braking motor system

  • Strategy to ensure consistent electrical and mechanical efficiency outside the motor under test

    • Custom mounting brackets, when needed
    • Proper coupling solution to ensure concentricity/coaxiality
    • Proper power connection strategy
    • Comparable cable lengths on all test motors

  • Redundant markers to ensure no slip anywhere in the rotor/connection stackup (paintmarks)

  • CTR Electronics in-house Dynamometer Software built using Phoenix 6

    • Data collection via CAN bus

Power Harness

All integrated motor testing uses the stock cabling that arrives with the product. Power/ground leads cut to a common length of 9.75 in (with the exception of the Spark Max, which was cut to a smaller length of 3 in, NEO leads left at their original lead lengths).

Software and Control

  • All motor controllers had current limiting disabled, and were commanded using 100% duty-cycle over CAN bus.

Motor Performance Curve Testing

Test Setup

  • Mechanically & electrically install the new motor into the dynamometer.
  • Confirm torque sensor tare is accurate. This involves a procedure that profiles the tare point and confirms it is near zero.

Initial Test Run

Utilizing the dynamometer software, drive both the test motor and braking motor in the same direction at 100% output (effectively applies little to no brake).

  • Confirm redundant markers are present and aligned at all torque couplings and potential "slip" locations.
  • Motors under test are run with no current limit in place, under 100% commanded output with no in-line circuit breaker or fuse.
  • Motors under test do not receive any active "thermal assistance" such as an outside fan, external heat-sink or other method.

Utilizing the dynamometer software, increase the brake amount marginally. Pause, and wait a period of time before taking readings. This eliminates many sources of error including error stemming from the rotor inertia.

Repeat sampling at chosen intervals until load exceeds 1Nm (for FRC size motors this usually terminates around 65 Amps).

For each sample, the dynamometer software reports/logs: torque, supply current, supply voltage, velocity, power, and efficiency.

Test Validation

Confirm the redundant markers are still aligned and no slip occurred during the test run.

Review Data:

  • Validate the supply voltage was constant and sufficient (Typical error < 0.3%)
  • Confirm Torque vs Current linear regression: R^2 > 0.999
  • Confirm Current vs Velocity linear regression: R^2 > 0.996
  • Confirm Torque vs Velocity linear regression: R^2 > 0.996
  • Check for outlier data points in current vs velocity, torque vs velocity, torque vs current, velocity vs efficiency.

Repetition for Data Repeatability

  • Wait in between tests to ensure all components properly return to ambient temperature
  • Repeat the procedure at least three times
  • Confirm values are comparable across three runs
  • Repeat test procedure with FOC enable/disable flipped
  • Repeat with additional motor sample(s) as desired.

Data Reporting & Extrapolation

Each motor is tested 3 times in a single configuration. This results in 3 runs for trapezoidal commutation per motor and 3 runs for FOC commutation (when supported). Each run is compared to each other to confirm consistency.

At this point we now have the extrapolated linear regressions to generate torque and current as a function of velocity. We also have linear regressions to generate torque and velocity as a function of current.

Once we've identified the key performance numbers, we are able to generate the full motor curves as a function of velocity.