[bdebde]

Found this:

To set up for twin BLMs operations:

1. Make 3 sets of Y-lead out of heavy gauge wire.
2. Insert the pinion gears onto the motors shaft. Do not tighten the set screws at this stage, the pinion gears have to be free to rotate on the motors shaft.
3. Mount the motors onto the model.
4. Connect the Y-leads to the motors and ESC. Please take note of the connection in accordance to the colour of the wires.
5. Run the 2 motors together at low to medium speed for a couple of seconds. The spur gear should not turn as the pinion gears are free to rotate on the motors shaft.
6. Disconnect the battery.
7. Apply some good quality thread-lock to the set screws and tighten the set screws to the pinion gears. Be extremely careful not to turn the pinion gears, spur gear or the motors shaft as they must remain at the position where they stopped.
8. Use an oscilloscope to confirm that the voltage generated by the 2 motors is in phase (as shown in the photo). The ESC will now treat the 2 motors (or even more than 2 in other applications) in sync as a single unit.
9. A less accurate method is to use a Multimeter (set to AC current) to check the phase-phase current between the 2 motors. Disconnect 1 set of Y-lead and connect the Multimeter probes to the original lead of the 2 motors. The current measured should be in the order of 0.1mA if the spur gear is turned by hand.
10. You must use step 8 or 9 to confirm your setup. The ESC can still run the 2 motors even they are way out of phase. In such case, large amount of current will flow between the 2 motors and if you turn the spur gear by hand (with all 3 Y-leads connected to the motors but the ESC disconnected), you will feel a braking effect or resistance (The motors are now acting as generator and motor in turn).
11. Other considerations:
(i) The backlash of the gear train may affect the phase angle of the 2 motors.
(ii) The close proximity of the motors may cause cross coupling by stray magnetic Flux.

So, looks like running them will synch them up?