Open loop power

I am controlling a Roboteq with an analog 0-5V open loop. As noted this is a power command. An increase in voltage increases both speed and power. What is the ratio? How do I get good power at low speed. Or should this project be a Toque mode?

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Drive HBL2350
Brushless Servo Motor

In open loop, the power is the PWM ratio. At 50% power, this is the equivalent to giving half the battery voltage to the motor.

If you want power at very low speed, then the best is to add encoders on the motor in order to sense speed and run in closed loop speed mode.