WTF is Duty Cycle?

VESC Bible Tuning and Riding
1

What is duty cycle and why do we care?

Note: If you want to know all the details on duty cycle and how exactly it works and what it does - google it. This is not the purpose of this page

Alright - so here it is for us Onewheelers: Think of duty cycle as a measure of a motor’s capacity to make a motor spin faster.

At 100 percent duty cycle you’re at max speed. As you accelerate your duty cycle increases until you hit max duty (technically 95% is usually the safe maximum a controller can handle).

Another Note: there’s more nuance to it at very low speeds, but if you remember just the above statements then you will be fine!

Voltage Dependence

Your max speed (aka 95% duty cycle) is pretty much directly proportional to your pack voltage.

On a fully charged Onewheel with stock 15s (63V) battery 95% Duty Cycle will be around 20mph.
When the battery is empty 95% Duty Cycle will be around 16mph.
see note about field weakening down below

Using a 20s aka 84V battery 95% duty will be 30 percent higher, due to the 30 percent higher voltage.

Why does duty cycle fluctuate so much?

In short: Voltage sag
When you accelerate you use more amps. Amps drawn from the battery cause the voltage to sag, i.e. to decrease temporarily. So the consequence is that you will hit 95% duty cycle sooner.

If you’re cruising downhill your battery will not sag, or sag much less, so your speed at the same duty cycle will be much higher.

Note on Field Weakening

It is possible to extend the top speed by adding field weakening current. With 30 Amps of field weakening speed at 95% duty cycle will be another 30-50% higher

See other pages here for more details on field weakening

What happens when I hit max duty cycle?

Once you're at 95% duty cycle that board is no longer able to accelerate you further. The controller is able to safely maintain that speed at 95% duty but it may still cause you to nosedive because balancing requires the ability to accelerate/decelerate the motor...

In short: try to remain below 95% duty at all times :slight_smile:

How do I configure my VESC to maximize duty cycle?

You don't - it works itself out. None of the config choices affect it. It is only affected by your battery voltage, how much/little it sags, and how you ride.
3 Likes
2

How is going uphill affecting duty cycle?

I would believe it raises the duty cycle. If that’s true does it mean that if duty cycle is lower then 95% it is possible to go faster uphill or do the motor “run out of” torque?

I have no plan doing any speed records going uphill. But it would be nice to know I’m still in a safe zone when going uphill :sweat_smile:

3

duty cycle when going uphill scales down a bit due to voltage sag.
you can only run out of torque if you hit your max motor or battery amps

4

ChatGPT, what is an easy explanation for duty cycle in a pev?

ChatGPT Answer:
In a PEV (Plug-in Electric Vehicle), the duty cycle refers to the percentage of time that the electric motor is actively powering the vehicle.

The duty cycle is determined by the driver’s use of the accelerator pedal, which controls the amount of power that the motor produces. For example, if the driver accelerates gently and maintains a steady speed, the duty cycle may be relatively low because the motor is only providing enough power to maintain that speed. On the other hand, if the driver accelerates aggressively or climbs a steep hill, the duty cycle will be higher because the motor is producing more power to meet the demand.

A higher duty cycle means that the motor is working harder and using more energy from the battery, which will result in a shorter driving range. Therefore, it’s important for PEV drivers to be aware of their duty cycle and adjust their driving behavior accordingly to maximize their vehicle’s range.

1 Like
5

@surfdado How about we add it to FAQ - Frequently Asked Questions (Wiki) - #6

Or as an alternative, we can setup a glossary.

6

Glossary is a great idea idea, but I’d want to keep this particular page on its own (we can of course link to it from the glossary, but there should be a single paragraph summary for duty cycle in the glossary)