There's a trick to setting ESC endpoints with a 7200BX in the mix.
Remove blades from the heli. You will need the motor connected so remove the blades and make sure the rotor hubs are clear of any loose clothing or drapes or other stuff that can get tangled. The motor should not start spinning during this process, but just in case it is vital to take these safety measures. It is easy to do something out of step and end up spooling it up accidentally.
Set the transmitter's throttle curve setting so that it has a full linear diagonal 0-100 range.
Unplug the throttle cable from the 7200BX. Power up the 7200BX with transmitter on and throttle low. Throttle needs to be low to initialize the 7200BX so it will send out signals on the throttle line. But if the throttle is plugged in at this stage (and the ESC is powered up) it will cause the ESC to initialize instead of entering endpoint programming mode.
Once initialized, move throttle on Tx to midstick. Go into servo travel settings for the throttle channel and move the min and max to 25% and 75%. The actual values will vary based on transmitter type/brand, but you're wanting the two points to be closer toward the middle of the range so you can "creep up" on the high and low points during the next steps.
Plug the throttle into the 7200BX and power up the ESC (if it isn't already) with the throttle still at mid-stick. The ESC will beep (motor will beep actually) a couple times and then you move thottle to full up position. Then goto servo travel screen and adjust the MAX setting until the ESC beeps. Add a couple/few more points upward servo travel. Then move the throttle stick to low position. Change the min servo travel until the ESC beeps and initializes. Add a few more points of travel for safety.
All done. Disconnect power. Change throttle curve back to what you want it at. Leave the throttle channel servo travel settings where you ended up with them.
Power up the 7200BX one more time to make sure it initializes with the low stick position still. If it does not you will need to make the min throttle servo travel value lower until it initializes. This will create a deadband in your low throttle position for the ESC, but it is a necessary evil in order to get the 7200BX to see a low enough signal to consider it a low position and initialize.
