AX2850 encoder time base issue

Hello,
I am using an AX2850 motor controller in a robotics project and have a question regarding the encoder module. The robot uses two NPC-B81 gear motors, and I am trying to use them in closed loop dual speed control mode. We put a 40 tooth ferrous gear on each axle with a two-channel quadrature output hall-effect sensor reading the teeth of each gear. I am receiving values and it appears to be reading properly, but the issue is this: I cannot get the encoder to read from the gear using the full -127 to 127 range. The motors only spin up to a little over 200 RPM. Setting the controller to use a time base of 64, and the PPR to 40, the max RPM is 2862, which means running our motors at top speed only allows us to effectively use values from about -11 to 11. What can I do to allow the encoder to give us the full range of values, given our current setup?

Thanks,
Matt Lanting
Lawrence Technological University

Speed is measured by counting the number of quadrature transistion during the time base period. If you have a low number of counts per revolution, the time base will need to be longer.

Time base is limited to 64ms, and it cannot go any lower. Slower time base means also that you would get speed update information slower and this would not be good for the speed control algorithm anyway.

Try to use an optical encoder.