Quick little guide for those of you who wish to try overmodulation on 6.06 firmware.
Disclaimer: Do this at your own risk, If you have to ask “Should I run overmod?” the answer is no. This is intended for users who understand the risks and know their way around building and tuning DIY Vesc boards and are OK with taking a fall if something goes wrong.
Overmodulation Basics:
Without getting too deep into this, and into territory I don’t really understand myself, Overmodulation changes the motor drive waveform from a sin wave into something closer to a trapezoidal shape. It kind-of chops off the top of the sin wave, Increasing the area under the curve driving the motor. Put another way, it increases the effective voltage that gets to the motor thus increasing the motor speed.
Overmodulation also scales the duty cycle, overmodulation 1.00 and overmodulation 1.15 duty cycles are not the same. You will see lower duty cycles because the sin wave motor drive is compressed into a smaller portion of your new duty cycle. There is a chart below.
This overmodulation is done with a variable. No higher than 1.15 is officially recommended. 1.10 is likely more appropriate, however other users have run as much as 1.21. If you stop reading here and set 1.21 you should know that there is no way for you to know it will drive the motor properly when overmodulating. The motor drive may work fine, It will likely be a little bit grumbly or less smooth, It may also drop you.
Why potentially run Overmodulation?
The main advantage I see from running overmodulation is allowing you to utilize closer to the max output of sin wave motor drive. If you treat overmodulation as only “extra headroom” it allows you to fly a little closer to the sun and have some extra to keep you and your board balanced when you inevitably hit something at speed and need the extra output. All things equal you end up using a little less field weakening since your duty is now lower so the board feels much more solid at speed.
Validate motor drive?
Sales pitch aside, you need to ensure the motor will work as intended during overmodulation. This is done at near 95 duty cycle. (above 86.4 duty on overmod 1.10 or 82.6 duty on overmod 1.15)
My first suggestion would be to know your current setup is 100% reliable.
Next test the free spin speeds with and without overmodulation. This is a good indicator that overmodulation is doing what you expect. Some controller and motor combinations show higher free spin speeds and others show no increase. This doesn’t mean the controller will fail to drive the motor while overmodulating and also having higher free spin speeds does not validate the motor drive either, it is just another indicator.
Following this I recommend testing on a treadmill (powered off, using it as a load / resistance) at a low state of charge. I personally tested with various field weakening values and with and without haptic buzz. This isn’t easy to do. Ashton at Atlowshop has a short video or two showing this technique.
Alternatively you could fully gear up and test at a very low state of charge on the road, however this may not be reasonable depending on your motor and battery voltage.
Duty is Scaled?
Overmodulation scales the duty cycle based on the overmodulation value you input.
The motor drive only overmodulates the waveform above the traditional 95 duty of sin wave motor drive. (above 86.4 duty on overmod 1.10 or 82.6 duty on overmod 1.15)
If you decide to treat this overmodulation as headroom it means you should not exceed those duty cycles during normal riding.
What this means practically is that you should lower your pushback duty in Refloat CFG.
My pushback recommendations would be dependent on your level of risk. I would use your prior pushback duty as an indicator. Please keep in mind we already should not be running 88 duty pushback on refloat 1.1 as duty pushback and haptic is smoothed meaning spikes will be less likely to activate pushback early.
| Overmod 1.00 | Overmod 1.10 | Overmod 1.15 |
|---|---|---|
| 80 | 77 | 76 |
| 85 | 80 | 78 |
| 88 | 82 | 80 |
Do not be deceived, overmodulation is not “doing something” because your duty cycles are magically lower after setting overmodulation to 1.15. Your duty cycles are indeed lower but they are simply scaled down, leaving room at the top of your duty cycle for the additional overmodulation headroom.
I know the risks, are there any other reasons not to try it?
If your battery not up to the task. You will likely scale the motor output up 10% or 15% beyond what you normally use simply because you can ride faster. I would avoid this all together on anything but the highest end batteries.
Don’t bother If you are overheating your controller regularly. This will just add more heat.
If you don’t care about going fast or don’t really run into duty cycle limitations. There is little need on high voltage builds outside of the very fastest riders. If you treat this as overhead only you will only gain 5% to 10% more speed out of overmod 1.15
Currently validated configurations (treadmill or high duty log)
Me:
Focer 3.0 (rion) - XR Hypercore - 19s - Ortega Original, No saturation compensation
Drives the motor fine at field weakening up to 45a but is a little less smooth. Haptic was also intermittent or quieter.
Focer 3.0 (rion) - SF HS - 19s - Ortega Lambda Comp, No saturation compensation
Drives the motor fine at 50a field weakening. Smooth. Did not test overmodulation haptic
Nexinty:
Floatwheel XRv kit - SF HS - 18s / 19s - Ortega Lambda Comp
Drives the motor well in overmodulation and is smooth.
Additional Resources:
Vesc Development Thread: Discord
Scaled duty estimates:
