Exploit That Speed Control

Mar 18, 2014 No Comments by

Modern speed controls come with a myriad of features that many of us don’t know about or use. Why? Well, most of the time the factory preset defaults are good enough, but what if they aren’t? What if we’re doing something weird or getting some weird actions from the motor and don’t know why? Check the speed control settings and read the instructions!

It’s said that instructions are just one person’s opinion and that may be partially true, but I can assure you that many of the questions I receive could be answered if the writer had read the instructions. Also, don’t disregard the help files. In particular, Castle Creations help files can answer a lot of questions.

TOOLS FOR PROGRAMMING
Most modern speed controls have some sort of programming card or USB interface device to help you access the program mode. I’ve never seen one that didn’t allow you to program it through a series of throttle stick movements from the transmitter, but this can be cumbersome at best. It’s a great tool if you’re at the field and need to change something, but be sure to take a cheat sheet with you so you’ll know what all the sounds and lights mean as you do it.

I prefer a USB or programming card because I’m lazy and it shows me exactly what’s going on. The USB device also allows you to access help files and update firmware as it becomes available.

MIND THE LEDS
Practically all speed controls now employ some sort of error or status code that flashes through an LED. Some indicate normal operation and others show nothing unless there is a problem. If yours uses an LED, take a copy of the signals and their meanings with you to the field. I never remember what each one means — especially if I’m using more than one brand of speed control.

WIRE THE SPEED CONTROL PROPERLY
This is a real safety issue. After a recent discussion about arming switches, I received way too many emails with descriptions of how users have cut the signal wire from the speed control to the receiver and installed various types of switches, etc. in the line. The reasoning was that if the speed control doesn’t receive a good signal from the receiver, it wouldn’t arm. This couldn’t be further from the truth. There is only one way to ensure a speed control won’t arm: remove all power! Depending on the control’s programming, to ignore power if there isn’t a signal is a fool’s folly.

CASTLE CREATIONS’ NEW WHITE WIRE

Most manufacturers have the means to program speed controls without using the transmitter stick method. Some of these are standalone and others can be used alone or as USB devices.

This new AUX line is designed for several applications and is completely different than the signal wire on the line from the speed control to the receiver. It offers the ability for helicopter pilots to remotely adjust their gyro’s gain or obtain rpm from 3-axis gyros that support sensors. The real plus for airplane fliers is the ability to provide one more level of arming safety. Right now, each of the controllers in the new Edge line comes with a coupon for a free Arm Lock Harness. Think of this as an additional arming switch with a “remove before flight” flag attached. When this plug is installed and the “key” is inserted, the speed control will not fully arm; when it is removed, the speed control arms completely. If the motor is running when the plug is inserted, the motor will stop. It is also possible to plug the white wire into an unused channel of the receiver and assign this as an arming switch. If the level of the assigned switch is below 50%, the speed control won’t arm. This allows radios without a designated throttle cut/hold function to have one. This new AUX wire is a great addition to controllers, but remember it is a secondary safety device. There is only one way to ensure a motor is not armed: remove all power!

GOT DATA?

The AUX wire is wired to a lock harness and is completely different than installing a switch in the receiver’s signal wire. Never cut the receiver’s signal wire or modify it.

More and more speed controls provide some means to log data during a flight. A lot of folks say they don’t care about telemetry and such, but knowledge is power when it comes to diagnosing problems. If your speed control can log data, use it! You don’t need to check it after every flight, but I recommend doing a baseline reading with a new plane. This gives you something to compare later data to if a problem develops. It can also answer questions about props and why one does better than another. Seeing how they unload in flight can tell you a lot. It can also answer some timing questions if you’re tweaking a setup and find that things are getting too hot. If your speed control doesn’t log data, you can install a third-party data logger from someone like Eagle Tree Systems and get a good picture of what’s going on.

6 Rules for a Happy Speed Control

  • • Read the instructions thoroughly
  • • Never cut the signal wire
  • • Always test with props removed
  • • Keep wires as short as possible
  • • Check to see if default settings match your application
  • • Never trust that a system is unarmed unless there is no power connected

KNOW YOUR COMMUTATION FREQUENCY

I saw your eyes glaze over, but stay with me. Most speed controls have switching frequency or pulse-wide modulation choices in the settings. A lot of the time, the default is fine, but knowing the commutation frequency will allow you to choose the best setting and increase efficiency. There is an easy formula to figure this out: (number of motor poles * motor rpm) / 20.

DBY Power Battery Checker

Here the checker is plugged into a 3S pack and shows the voltage of each cell.

The side of the case has six plugs for up to 6S packs.

The bottom of the case has plugs for receiver packs and external power from a JST plug.

Monitoring and maintaining our batteries is a big deal in electric flight, and the DBY power battery checker (dbypower.com) has a small price tag and is a huge help. I discovered this gem on the Heads Up RC website (headsuphobby.com) and figured for the price (less than $20), I’d give it a try.

This three-in-one checker is good for up to 6S packs of either LiPo or LiFe cells and will give you a status of the individual cells by just plugging the balancing plug into the appropriate plug on the side. It can also be programmed to balance or discharge. I plugged a 3S pack of LiPos in, set the discharge for 3.8 volts, and watched as it discharged and balanced the pack to the proper storage level. It does get fairly warm as it discharges because it doesn’t have a cooling fan, but it gets the job done and within .003 volts. It can also be used to check the status of receiver packs, but requires an external power source through a JST connector on the side. This is a pocket-size checker that will do more than most and is now a permanent part of my field equipment.

Practically all motor manufacturers provide a data sheet that will tell you the number of poles in a motor. Multiply that by the projected rpm of the motor (just multiply the Kv by the voltage) and divide the result by 20. Easy! Here’s an example of how that will work:

(8 * 24,000) / 20 = 9,600

An eight-pole motor running at 24,000rpm will have a commutation frequency of 9.6KHz (9,600) commutations per second. My speed control shows that the “outrunner mode” is 8KHz, and there are 12KHz and 16KHz settings. In this case, I would choose the closest to my 9.6KHz result. Not all speed controls label a setting as “outrunner,” and you can see you might come up with a situation where that setting might be too low even though it’s an outrunner.

Left: Keep a copy of your speed control’s LED cheat sheet in your radio box so it’s available at the field for diagnosing problems. Right: This is a copy of my transmitter’s adjustable settings. I keep this just in case I need to do a transmitter method at the field.

CONCLUSION

You don’t have to be an engineer to fine-tune your electric flight system; if you did, I couldn’t do it. With a bit of reading and paying attention to your speed control’s instructions, you can fine-tune it or troubleshoot it without frustration. Don’t accept a system that isn’t operating quite right — fix it. Study the help files and experiment with the prop removed. Most speed control problems can be traced back to operator error, and I’m proof of that.
BY GREG GIMLICK

Electric Basics

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