How many times has this happened to you? Saturday morning, wake up early to throw together those parts that arrived during the week…frame, motors, ESCs, flight controller and more…can’t wait to fly this thing. Rush it out into the back yard, power it up, add some throttle, and nothing…or worse, smack, an instant and violent crash, or even worse smoke, lots of smoke. I’ve done all of these more times than I care to admit, so here is a simple guide that will hopefully avoid the sunny weekend looking a busted quad.
Avoid the smoke
Double check all of the connections, especially the ESCs. Reversing the + and – on an ESC can fry everything. Lipo batteries can dump a hundred amps or more into a shorted or reversed connection, so using one of these can limit the damage. Don’t connect a battery for the first time until you’ve done some of the steps below.
No props for now
Don’t put the props on yet. There are several steps to do before you are ready to trust your new build with props.
Setup the ports
Plug your new rig into the RaceFlight configurator (RFC) and make sure your flight controller has the latest firmware. After that start your work on the RaceFlight ports page. You’ll need to configure one port for your receiver connection. How you do this depends on what type of receiver you have. Generally Sbus and Spektrum Satellite receivers should be connected to one of the UART ports. Save and reboot.
Next look at RFC’s configuration page. There are a ton on options here, but you only need to start with a few to begin with. Under the ESC/motor features, I like to turn on the MOTOR_STOP feature so my motors don’t spin up right away when I arm the quad. Also enable ONESHOT125 or MULTISHOT (but not both!!) to match the capability of your ESCs.
You should make sure USE_PWM_RATE is turned on. You will likely need to turn on SBUS_INVERTER if you are using an Sbus receiver. Don’t go crazy with the loop control yet. Choose something reasonable like M4.
For the receiver mode, choose the option that matches your receiver connection. Many receivers are serial these days, so for those choose RX_SERIAL and then select a Serial Receiver Provider.
Fail Safely! Make sure you have Receiver failsafe turned on. This tells the flight controller what to do if your receiver looses contact with your RC transmitter. In most cases you just want to go to minimum throttle which is 1000.
Leave everything else on the configuration page at its default setting. Save and reboot.
Now it’s time to make sure your motors and ESCs are connected correctly and working, so go to RFC’s Motors page. Please make sure your props are off for this step!!!
Connect a battery and click the “I understand” switch. One by one use the motor sliders to spin up your motors. You don’t need to spin them very fast – that could damage the bearings because without a prop attached they will over-rev pretty easily. You just want to verify that the motors are connected in the right order and they are spinning in the right direction. Also they should spin smoothly without twitching or excessive vibration.
[Calibrate ESCs here????]
Here you want to make sure your transmitter and receiver are bound and working well together. Make sure your receiver is powered up (you make have to connect a battery to do this) – props should still be removed! With your transmitter sticks at neutral (row/pitch/yaw centered and throttle at minimum), you should see the received roll, pitch, and yaw values as close to 1500 as possible in RFC. Most transmitters are a little noisy and won’t stay exactly on 1500. This will cause some drift while flying unless you add some RC Deadband and RC Yaw Deadband. I usually set the deadband to 4 or 5 for both.
Also make sure that when your transmitter’s throttle stick is at minimum, the received throttle value should be below 1100 [?? need the exact value]. If it is not, then you may have trouble arming your quad. You will have to make adjustments on your transmitter to make the numbers on this page look ok. Don’t forget to save when done.
Arm and Throttle
Now it’s time to arm your quad and briefly spin up the motors without props attached. If there is going to be a violent problem, I’d much rather find out about it without the props on.
You want to be in rate mode to do this so your quad will not try to self level. Rate mode is the default and should be active unless you set up a flight mode switch on the RFC’s Modes page already.
To arm, simply move your stick to min throttle and full right yaw for about a second and then go back to min throttle / neutral yaw. Then add a little throttle until the motors spin up slowly. Be ready to cut the throttle quickly.
Listen for any twitching or unusual vibrations. I have had quads freak out at this stage, going to very high RPM or shaking wildly. The causes can be many – I may write another article about how to debug the issues that come up here. It’s a good idea to click over to RFC’s Sensor’s page and look at what the gyro readings look like with the motors spinning. You will see some vibrations for sure, but you should not see glitches or twitching. Small unibody quads can transfer a lot of vibrations to the gyro. If you see twitching, you may want to mount your flight controller using better vibration isolation.
If all is well so far, then you are pretty much ready to fly. Unless you have a really unusual quad, you shouldn’t have to do any PID tuning at this stage. Raceflight’s default PIDs work well for most small quads (150 to 250 mm frames).
You may also want to set up a flight mode switch to activate Angle or Horizon modes if you prefer to fly with self leveling assistance. Using rate mode will make it easier to debug any stability issues on a new quad. Trying to debug a problem while using Angle or Horizon modes just adds another layer of complexity.
These steps should cover the basics of getting a new quad in the air running on RaceFlight. Look for other articles explaining some of RaceFlight’s more advance features.1