Here are a few tips I have picked up while researching which ESCs to put on my quadcopters.
On a quadcopter, the flight control board’s firmware monitors measurement devices like gyros and accelerometers along with pilot stick inputs and sends signals to the ESCs attached to each the four motors. The ESCs use these inputs received from the flight control board to deliver the power required to control the speed of the motors. Each ESC has a processor, firmware and other electronics that manage this task by rapidly switching the power to the motor on and off. Continue reading for some tips on choosing the right ESC…
Max Amp Rating
Brushless ESCs are used to control brushless motors that are used on most quadcopters. The maximum amperage an ESC can handle needs to be greater than the motor/prop combination will draw. If the amperage rating is not high enough, it could overheat and die.
Other Things to Consider
Since quadcopter flight control boards need to make exact and minute adjustments to all four motors within a fraction of a second, off the shelf ESCs may not do the best job of stabilizing a quad. Two possible problems with off the shelf ESCs are:
- Not handling fast refresh rates
- ESC firmware that is not optimized for quadcopters / multicopters
Handling Fast Refresh Rates
Signals are sent from flight control boards to ESCs at rates of 400Hz or more. This translates into 400 or more updates per second. Some older ESCs may not be able to handle these update rates. The faq on the MultiWii wiki page states:
However, according to this post by Timecop at rcgroups.com, many modern day ESCs have this capability. So, while some ESC vendors advertise that they have update rates of 400Hz or greater, it appears many cheaper ESCs accept these speeds too. Whichever ESC you choose, ones that accept faster refresh rates are a better choice for a more responsive and stable quadcopter.
Even ESCs that can process high refresh rates probably have firmware that is not optimized for quadcopters. Luckily, a fellow named SimonK has written firmware that is optimized for quadcopters and it can be loaded on to many common ESCs. This requires that the ESCs be reflashed. Since flashing requires some skill, tools and effort, it may be best to purchase ESCs that have been flashed by someone familiar with the process. Here is an rcgroups post that lists a few folks selling ESCs flashed with the SimonK firmware.
For those brave enough to try it themselves, the rcgroups thread on reflashing and the open pilot wiki on flashing are two excellent sources of information about flashing ESCs with SimonK’s firmware. Beware, if it doesn’t work, the original firmware is gone forever unless you have a copy of the original code. Also, SimonK has different versions of his firmware for different ESCs and it is important to use the correct version.
ESCs should be chosen that will handle the maximum amperage drawn by the motor and prop it will drive. ESCs that accept fast refresh rates should be chosen and many inexpensive ESCs have this capability. Flashing ESCs with firmware that is optimized for multicopters is a good option to get maximum stability. However, the process of flashing requires the right tools and firmware and there is probably no going back if it doesn’t work.