Hello,

The Pod product descriptions mention brushless DC motors. A quick search in the forums gave 2 threads matching "brushless", apparently mostly concerned with servos and steppers.

Other threads mention that the PWM outputs come in pairs that are synchronized with a "dead-band" to prevent a direct short circuit through a single half-bridge. I suppose this is configurable to cope with differences in switch-on and switch-off times in different MOS-FETs.

I also believe I've seen in one thread that three pairs of PWM outputs can be synchronized to drive a 3-phase motor.

The brushless DC outrunners are awesome motors for direct drive electric flight (model aircraft) with RPM in the range 1000 to 10-15000. The Peter Rother site http://www.aerodesign.de/peter/2001.../index_eng.html
provides loads of information on the operation of these motors. Each full PWM cycle (6 pulses in proper permutation) will rotate the motor 1/7 of a 360 deg turn (for a 14 magnet motor).

Each pulse is created by connecting one of the three motor leads to the battery, and one to ground (meaning one half bridge must receive a high-side on, and one half bridge must receive a low-side on - the third motor lead must be disconnected during this pulse, and all three are disconnected between pulses). The pulse frequency must be synchronized to the required motor speed, and the duty cycle adjusted to give exactly the torque that will keep the actual rotation speed in sync with these pulses. The phase relationship between the rotation and our pulsing will need to be fine-tuned (based on speed and load) to provide maximum torque with minimum power consumption (and minimum power loss in the electronics - essential to keep the electronics cool and the batteries long-lasting).

I would like to use the International Rectifier 3-phase driver IC IR2133 with 6 suitable power MOS-FETs. These driver IC's take care of the required dead-band, so this function may probably be disabled in IsoMax. At first sight it looks like the IC is only suitable for large AC 3-phase drives, but it is just a modern integrated version of the three IR2101 half-bridge drivers seen in Actronic speed controllers for small Actro DC brushless outrunners.

The first task at hand is to create the correct PWM pulses to the 6 driver inputs. Are the Pods geared towards grouping three pairs of PWM outputs into this exact permutation scheme with hardware only, controlled by one frequency setting and one duty cycle setting? Or do we need to divide by 3 or 6 somewhere to space the pulses correctly between phases, and program each pair of PWM outputs separately? Does someone have a code example at hand?

Regards, Terje