Talon vs. Talon SR

Can someone explain (to a simple programmer) the difference between the Talon and Talon SR?
What is the practical difference between “Locked Antiphase Rectification” and Synchronous Sign Magnitude Rectification"?
Was the change made to address any specific problem or application?

Generally speaking, you shouldn’t see any impact from the change. From what I understand, it is supposed to give the same motor performance (in other words, you can swap one for the other and not notice a difference in how the robot drives), but provides lower temperatures in the Talon itself when the motor is stalled. This means the Talon will be less likely to burn out when used.

from the Web:


locked-antiphase allows for regenerative braking. Unfortunately, the low inductance of most brushless R/C car motors results in very quick current changes in the phase windings. Since locked-antiphase depends on the winding inductance to smooth out and reduce circulating/ripple current, this was a major problem; at reasonable PWM frequencies, the ripple current was very high – while, at high PWM frequencies, the MOSFET switching losses were unacceptable.

Switching to sign/magnitude resolves most of those issues, but introduces some of its own. Most importantly, the body-diode on the MOSFETs must now come into play during PWM off-cycles. The body diode is a lot higher loss than the MOSFET, so it results in more power dissipation. Synchronous rectification would help with this, but would be tricky to implement in firmware (especially given the rapid current decay rate). Many dedicated motor controller ICs have integrated hardware for implementing synchronous rectification.


Locked-antiphase PWM is somewhat counter-intuitive and at first seems like it would just burn up a lot of power. The motor is alternately driven forward and then reverse; this actually works because the motor’s inductance low pass filters the current to a DC value. At 50% duty cycle the average current is zero, and so the motor remains stopped. Increase the duty cycle and the average current becomes positive and the motor turns “forward”.

Of course, the motor isn’t a perfect low pass filter, and the resulting waveform will have ripple. If the motor has too little inductance for the PWM frequency used, then there will be a lot of ripple and the power loss will go up. You’ll also be able to feel vibration in the motor when it is stopped.

See also Pages 17 & 18 of this PDF from Siemens:


Still absorbing the material, and I will likely have additional questions, but thank you for the links.

According to Mike Copioli (from CTRE) it means that the Talon SR will run cooler when stalling the motor. Aside from that, basically no practical difference. Technically speaking, Talon and Talon SR would behave differently when outside forces (like gravity, on a slanted surface) are contributing to the drive force. Mike says the difference in practice is negligible to non-existent.

Check out the latest user manual (text in orange) …

…or andymark…
…for the details but basically Talon SRs are more efficient at stall (less heat), expanding the no-fan usecase. Also the led blink pattern is more distinct between Full throttle (full forward/reverse - led solid) and “Less then full” throttle (99.999% in either direction - led blink). Led blink rate still indicates magnitude though (just like before).