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May 20, 2018, 10:29 PM
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Speed Control Failure

If an Electronic Speed Control (ESC) fails in flight there may not be power to the receiver to operate your servos. The result will be a loss of control and possible crash damage to a person, place or thing. If the ESC fails on the ground before or after takeoff the risk of crash damage is still present but is minimized. The use of seperate receiver and servo battery power can be used or a back up pack but you will still be faced with a power off landing that might be cause damage. This is how I usually verify and validate new or suspect speed controls.

1. Measure the amp load (using a Wattmeter/ Current meter) and confirm it is below the rated amp load for the ESC. The amp load can be reduced by changing to a lower pitch prop or a smaller diameter. Reducing the cell count for example from 6 to 5 lipos will reduce the amp load.

2. Run the motor for at least 10 seconds with a prop and measure the heat of the ESC. Use an ingrared thermometer and ensure temps are less than 140 F. If you do not have one you should be able to keep your finger on the ESC for 3 seconds or more. If it hurts at 3 seconds the ESC is too hot and the resultant heat can affect or damage the internal electronic components. Increase ram air cooling and have more exhaust area than intake area. Keep the ESC from being insulated. Don’t glue the ESC to the wood or foam fuselage. Keep the heat sink out in the cooling air flow.

3. For new speed controls or used ones that you suspect might be unreliable taxi the model for 5-10 minutes on the ground. Use high power and reduce power to limit the taxi speed. Try not to take off. If the ESC fails right after takeoff you probably will have to land straight ahead and the result may cause damage.

4. After 5-10 minutes check the heat of the ESC. Most likely the ESC will be hotter than if there is in-flight cooling air.
In flight there will be reduced current because the prop will unload. How much? Tom Hunt had an excellent article on using the Castle Phoenix ESC units with data collection. By downloading the data on the Castle software you can see the maximum amp load with full power in flight. There are approximate formulas for estimating the reduced current but the most accurate way is to measure by inflight data collection.

I recently installed a 40 A 2-6S ESC made by RCLander in my Maule float plane. With a 3S pack and 12x4 Timber prop I measured 32 amps forward and 34 in reverse. After taxiing on the ground in forward and reverse for about 5 minutes I put a fully charged 3S 3200 40 C pack and took off. Climbout was scale like and not steep. On the downwind I reduced power to off and then applied half power. I notices there was no power and so immediately turned toward base and final but I was too low and could not make the runway. The resultant landing on rough ground broke both of the floats away from their plastic mounts to the foam. At the site I still had flight controls and the ESC was slightly warm but not hot. I could not get motor power at the site. I carried the Maule and floats back to the pit table and checked again. After a few attempts the motor started to work. I checked the new Thrust 40C pack and it was showing 85% capacity remaining. Initially I thought it might be my 3 postion Aux channel switch that was programmed for +100%, 0%, and -100%. I figured that if it were in the 0% position it would cancel the forward and reverse out and yield no power. After repairing the floats and testing the ESC with taxi I did not see this to be the case. The 0% switch position would either stay at forward or reverse power but not go to zero power. I programmed my DX9 Digital switch E to have +100% in the 0 and 1 postion just to make sure. The 2 position remained program for reverse at -100%.

To make sure a subsequent ESC failure would not occur I tested the Maule by full power acceleration then reject runs on the grass runway. After the prop would come to a stop I would test out the reverse with full power. After doing this for about 5 minutes the Maule had no thrust and I had to carry her back to the pit table. The ESC was warm but not hot. Pack capacity was measured at 60%. I removed the RC Lander ESC at installed a 60 amp ESC that I was previously using for about 10 flights. There were no problems with this ESC. My conclusion is that the Turnigy RClander 40 A reverse ESC failed either from over heating and/or internal component damage/failure.

A few days later I received a new Turnigy AeroStar RVS 60A ESC and installed her in my Maule. I practiced forward and reverse taxi on my street with the amphib floats. With EPP foam wedged between the rear tires and balsa/ply mounts I had built in brakes to limit the speed and provide braking on the street. I noticed a different operation with this unit. After closing the throttle I could not change motor direction until about 1 second after the prop came to a stop. With the previous unit I could change direction as soon as the prop came to a stop. This operational difference should not cause a problem but might be a safety design to ensure there is not overloading the ESC components.

In 2 days I will be doing 5-10 minute high speed taxi testing on the grass runway before inflight forward motor flying. I also will be testing another prop that will provide approx 50 amps of power. A 4 cell will also be tested. In all cases I will be climbing to a “dead stick” position so I can glide back to the runway and not the rough field areas. I will report my findings in a week.
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