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Jul 16, 2015, 10:04 PM
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Discussion

Simonk Braking


Hello,
I'm building a robot with Hobbyking F-60A ESCs, flashed with the Simonk firmware, and need the controller to be able to change the motor speed as quickly as possible. I see two different ways of slowing down the motors, COMP_PWM and MOTOR_BRAKE. From what I understand, COMP_PWM does regenerative braking, putting the energy back into the battery, while MOTOR_BRAKE turns the energy into heat in the motor and FETs. Is this correct?
Does COMP_PWM run cooler?
Which one gives more braking force?
Which one reacts quicker to changes?
Do they work whenever you reduce the throttle, or only when you bring it to zero?
How do I find the optimal values for dead time?
Thanks!
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Jul 17, 2015, 02:49 AM
g0t rabb1t?
ABLomas's Avatar
Braking is only in "stop mode" - it does not slow down props, it only prevents them from turning again.
Comp_pwm does.
About dead time- measure it (but it's already in .inc file, set and correct for F-60A).
Jul 19, 2015, 11:43 PM
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I assume I would measure the dead time with an oscilloscope on the motor leads? Or do I put it on the FET gates? What am I looking for?

And the bs.inc file says the dead times were calibrated for F-40A ESCs. I tried flashing the bs_nfet version because this is an N Channel board but it didn't work. Why does bs.inc work when it says at the top:
Quote:
For HK Blue Series with n- and p-Channel FETs (old version)
Last edited by ahalekelly; Jul 20, 2015 at 12:05 AM.
Jul 20, 2015, 12:52 AM
g0t rabb1t?
ABLomas's Avatar
Hmmm, IIRC i used:
DEAD_LOW_NS = 300
DEAD_HIGH_NS = 300

For HK-60A.
But that was smth like 2 years ago... I can try to find old .inc files if that value does not work.
Jul 20, 2015, 12:56 AM
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300 seems to be the default for .inc files that have not been calibrated. The bs.inc file calibrated for the F-40A has these values, which seem to be working, but I'm wondering how to find the optimal values.

DEAD_LOW_NS = 1400
DEAD_HIGH_NS = 1700
Oct 07, 2015, 01:30 AM
hacker
Hello! F-60A and friends have changed PCBs a few times, so I'm not sure what the best values are for them. It's a bit of a nuisance, but you can check yourself by setting high values and lowering them until you start to see shoot-through. You can do this with no motor attached and an oscilloscope probe on the battery connection at the ESC, and some sort of "bad cable" (as I often use), like a cheap alligator jumper cable, to act as a sort of power resistor actually connecting the power source.

You can either trigger just off of the voltage at the ESC dropping below your supply voltage. If you also attach a second channel to a motor phase, you can see which "end" of the PWM cycle is causing shoot-through. When it occurs, the voltage will drop -- maybe just for some nanoseconds, but when this happens, additional heating occurs, and if it's excessive, it can damage things.

When it's set correctly, complementary mode should take no more power and usually be more efficient than with it off (since it avoids diode losses). Note that without drivers, the dead-time will become voltage-dependent. You should be fine on the F-60A, however.


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