Troubleshooting continues
Greg Gimlick | [email protected]
TAKING OFF: I'm going to continue with troubleshooting issues we discussed last time. I'll concentrate mostly on Electronic Speed Controls (ESCs), because often that is where problems lie and it's not always obvious.
Size Matters
Many problems people run into with a setup not running properly have to do with choices they've made and the reasons behind them. One such choice has to do with the size of the speed control. I'm not talking about physical size, but "electronic" size. They're choosing an ESC that just isn't up to the task.
If your setup is going to pull 60 amps at full throttle, you need to select an ESC that is rated for at least 60 amps, and I recommend going beyond that. A common argument is, "But I'm going to be flying at half throttle most of the time, so I thought I could get away with a 45-amp ESC." That doesn't hold water—or electrons!
At the most basic level, an ESC is nothing more than a switch. The controller is either full on or off; it turns on and off thousands of times a second and the time it's on or off varies by throttle position. All the way off means there is no power being sent to the motor; all the way on means power is being sent to the motor. Any throttle position between off and on means the ESC is switching on and off to achieve the power required for that position.
Why do we care? What it means is if your system draws 60 amps at full throttle, it also draws 60 amps at half throttle. It's only there for a microsecond at a time, but it's still 60 amps. You can't expect a 45-amp controller to handle the setup even at half throttle. If I'm planning a setup to pull 60 amps, I like to use a controller that is rated closer to 80 amps. That gives me plenty of safety headroom for spikes, etc. Bigger is better if you have the room.
Basic Rules of ESCs
- Read the instructions. This may sound elementary, but it's the number-one reason behind most of the questions I get and why people manage to damage equipment. ESC instructions are not exciting, but they are terribly important. They tell you about programming options and how to avoid damaging your airplane or equipment, and include important safety tips.
- Learn how to enter programming mode. The directions explain how to enter programming mode so you can adjust the ESC to fit your needs. Some controllers can be programmed with external devices, but all can be programmed through a series of stick movements on the transmitter while listening to the tones emitted by the controller/motor.
- Always remove the propeller (or rotor blades) before programming. Never trust an armed controller. Treat controllers as if they are about to start up, whether or not they have arming switches.
- Never leave a motor battery plugged into a controller when not in use. A slight current drain will eventually kill your battery, so always remove the battery when you're done flying.
Basic Settings
Controllers have myriad features that can be changed to optimize your system. Some you will use and others you will disable. In most cases, your controller will come with factory defaults that are suitable for 90% of user applications. Below are the most common elements.
Brake Setting
Most controllers let you decide if you want a brake set or not. The brake can be set to "on" if you want your propeller to stop when you reduce your throttle to idle/off. This is mostly used for folding propellers, but some prefer to stop their propeller for better glide with the motor off even if it's not a folding type.
There are settings for soft brake, hard brake, and no brake. The default for most manufacturers is no brake or soft brake, but again, read the instructions. Some Jeti controllers default to full brake. If you're flying a helicopter, be sure the brake is set to off.
Low-Voltage Cutoff
This feature ensures you don't damage your LiPo pack by drawing the voltage too low during a flight. The default on most controllers is "auto," and most of the time that is fine. Various brands use different methods to determine cutoff, but the standard is roughly 70% to 75% of the voltage level detected when first armed.
This is important because if you fly more than one flight on a pack without recharging between flights, the controller may misinterpret the number of cells and therefore allow the voltage to drop too low. A three-cell LiPo pack is fully charged at 12.6 volts and the nominal voltage is 11.1 volts. The ESC detects the cell count and sets the cutoff at about 75% (9 volts), assuming it sees 12 volts when you connect it.
Example: You make a flight and land with plenty of power left. After a break, you reconnect the same pack without charging and the ESC detects 11.5 volts. Now it sets the cutoff at 75% (8.12 volts). That's too low for a three-cell pack; you've discharged it to about 2.8 volts per cell and they don't like much below 3.0 volts per cell. This illustrates the potential problem with multiple flights before recharging.
Check your ESC instructions. Most ESCs will emit a tone upon arming that indicates how many cells the ESC thinks are in your pack. Verify it is correct before flying. Some controllers allow you to override the auto setting and select a minimum discharge voltage. Always fly with a freshly charged pack so the controller has the best chance of properly identifying the cell count.
Cutoff Mode
Most controllers allow you to choose whether you want a hard or soft cutoff when minimum voltage is reached. A hard cutoff means the motor will stop when the voltage is reached. A soft cutoff means the motor will pulse on and off to let you know it's time to land.
When the cutoff activates, you can often reduce your throttle to idle for a second and then return to normal operation long enough to land the aircraft. Don't abuse this capability; it is overriding the cutoff and meant to give you more control to avoid a dead-stick landing. Helicopter pilots will want a soft cutoff or likely none at all because a hard cutoff would stop the motor and put the heli into an autorotative state.
Start-up Mode
This defines how the motor starts when you open the throttle. Common choices:
- Normal — usually the default and fine for most airplanes.
- Soft start — eases the load on the motor and drivetrain at startup.
- Super soft start — even gentler for sensitive gearboxes or large rotors.
If you're flying an airplane with a gearbox, you might want a soft start to reduce stress on the gears and motor when starting. Helicopters generally need a soft start most of the time to soften the strain on the main gear while the motor attempts to get the rotor blades started. Using normal on a helicopter can often strip a gear.
Timing
Timing causes more questions than a paragraph or two can answer. The default for most ESCs is "standard" or "medium." Unless you want to dive into motor theory and optimize for competition, you're safe leaving this alone. The instructions will give special notes if your motor is not running smoothly.
Pulse-Width Modulation (PWM) Switching Frequency
Stick with the factory defaults unless there is a problem. If you encounter an issue, check the instructions or contact technical support. PWM switching frequency is the number of times per second a pulse is sent to the motor; this may range between about 8,000 and 32,000 times per second. A full description of PWM is beyond the scope of this column.
Operating Mode
Some controllers give the option of selecting a preprogrammed set of parameters such as "airplane," "glider," or "helicopter." When choosing one of these operating modes, the ESC will apply preset features to optimize that choice.
- Helicopter mode often activates a governor to help with throttle/collective coordination and uses the softest start mode.
- Glider mode usually sets a hard brake for folding propellers.
I'll discuss governor modes and helicopter specifics in the next column.
One Last Thing
I receive many questions about how to connect the three wires to the motors. This is easy — it doesn't matter. Hook them up in any order and if the motor runs backward, change any two wires. You won't hurt a thing. Some ESCs also let you reverse motor direction in programming.
Final Approach
There is much more to ESCs than we've touched on here, but I'll go into more detail on some of the features next time. This should get you over the main stumbling blocks and help avoid the most common problems.
I hope you all have a very happy holiday season and a great New Year! —GG
Sources
- Castle Creations
- (913) 390-6939
- www.castlecreations.com
Transcribed from original scans by AI. Minor OCR errors may remain.
