Brushless Motor Theory: Adjust ESC timing to control power and heat

My recent guide on upgrading the 144001, 124018 and 124019 with a drop in 2445 5400kv made for a very fast car but also generated a lot of heat for the motor and ESC. In this guide I have a brief look on the impact of adjusting ESC timing on power output as measured by speed and the resulting change in heat of motor and ESC plus efficiency.

Most cheap ESCs, notably the Surpass/Racerstar are impressive in that there is some basic ability to programme the ESC for throttle punch, dead band, low voltage cut off plus braking and reverse as you can see in this guide. Step up to a more premium ESC like the hobbywing 16BL30 and 10BL120 as recommended in my brushless guide and amongst other items you also have the ability to adjust motor timing.

Basic timing theory

In your internal combustion engined car the motor timing can be adjusted - the point that the sparkplug ignites the fuel in the ignition chamber relative to the piston location. The advance that is applied here compensates for the delay between spark and combustion (related to the octane rating of the fuel). I am oversimplifying things here but advancing timing can benefit power at the cost of efficiency. This relies on engine design fuel, rpm, throttle and other factors so as you can imagine there is no one generic timing ideal.

Much the same is true with your brushless motor but instead of a spark we are talking about the magnetic coil of the motor energising to create a magnetic field to rotate the stator - advancing timing can increase power but typically generating more heat and dropping efficiency. The difference is that this can be managed by ESC programming rather than physical angle adjustment on the motor (although this is true for brushed motors)

So although it is super fast (78kph on 2s), my 2445 5400kv drop in brushless upgrade runs hot and has been known to trigger esc thermal cutout. On any other car I'd look to drop the gear ratio (smaller pinion) but on this car the 15t is already the smallest pinion available. Although cooling solutions like venting, heatsinks and fans can improve I wanted to see if this could be helped with adjusting timing down based on the overly simplified theory that:

Increase timing

• More peak power
• More peak RPM
• More heat
• Less efficiency

Decrease timing

• ​Less peak power
• More torque at lower RPM
• Less heat
• ​More efficiency​

Well I have more speed than I know what to do with which means everything in the right column sounds ideal.

How to Decrease Timing

I decreased timing on my Hobbywing 16BL30 using the programming button next to the power switch but if you are not confident counting beeps and LED flashes then the programming card is much easier and not expensive. Note: this is different to the surpass/racerstar one.

​Hobbywing Quicrun Program Card For RC Car

Here is the magical programming button on the Hobbywing 16BL30 ESC

If you wish to use the programming instructions the manual can be found here but specially here are the programming details and parameters available for this ESC:

As you can see it is 11.25 degrees advanced from the factory meaning this is plenty of room to drop (or increase if that is your thing). Because I wanted to see a reasonable impact I went with reducing timing advance to 3.75 degrees. Read on for my results

Results for reducing ESC timing

Definitely slower but still fast - specifically I dropped 10kph top speed going down from 78 kph top speed to 68kph top speed. I didn't pick up on a noticeable increase of torque however punch was kept at the stock setting of 5 with plenty of room to take this up as high as 9 if I want.

11.25 degrees timing (stock)

3.75 degrees timing

Good news is that motor and ESC temp have definitely come back. I gave this car a good 10-12 minutes of hard street bashing in a large area meaning decent speed pulls, spinning out and accelerating hard again from standstill. After this the motor and ESC was hot but I could keep my finger on either for more than 3 seconds. At no point did I hit thermal cut off which did tend to be a feature of this setup in my earlier runs at 11.25 degrees advance. The 1800mah 2s battery I was using was just under 3.8v per cell at 12 minutes which is a 10-20% improvement in runtime on the previous setting so this is a nice little gain in efficiency as expected - less energy being wasted as heat.

It is worth noting that the ambient temperature has dropped about 5 degrees from when I ran with stock timing and I am enjoying the additional venting mods that I outlined in my original drop in brushless article. 

Conclusion

Decreasing the esc timing advance from 11.25 degrees to 3.75 degrees has definitely reduced the top speed to a more manageable level with the 2445 5400kv motor but has more importantly reduced motor and ESC temp. The difference is noticeable and was enough for me to have confidence that I would not overheat the motor and not hit ESC thermal cutoff along with the improvements I made to the poorly ventilated 124018. This simple change to programming on this excellent ESC means I can now run my car the way I want it without worrying about damage. I will test other options in the future but for now, this is exactly what I was looking for.

Next up I'll be looking at 2s vs 3s and bringing in a lower speed 3600kv motor to compare.

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