The guy in the video includes braking performance in his dyno pulls and again, zero detectable difference.

Going back to my simple circuit analysis, I think perhaps viewing the load as simply resistive rather than inductive may have hindered my understanding of what's going on. I mentioned the instant voltage changes you'd see without the caps in my previous post, but that only happens with purely resistive loads. With the inductive nature of the motor windings, when the switches close the voltage across the windings will not change instantly. The moment the switches are closed the inductor will act like an open circuit and over the course of 5 time constants it will change to acting like a short circuit. So in that regard I don't think the cap is doing anything to maintain a higher voltage during the PWM pulse that the coil isn't already doing itself.

Man, if I had a dyno and an oscilloscope I'd really love to dig into testing all of this to see what's really happening. Every youtube video I've seen where someone hooks up a scope to an ESC is showing the output to see how the motor is commutated. I haven't seen anyone put the scope on the battery side of the ESC to get a good understanding of ripple. I have to imagine there's some combination of motor kv, ESC PWM frequency, and capacitor value that could result in some interesting behavior.

I wouldn't expect to see ESC PWM frequency in a dyno run. Dyno runs are usually at full throttle, which is 100% duty cycle. That'll be a solid signal, effectively no PWM.

Some data. Purely observational, but different capacitor configurations have a measurable effect on ripple voltage.

Test rig was a Hobbywing XR10 Stock Spec with a GensAce 21.5

Test subjects were:
1) Standard electrolytic cap as supplied with ESC
2) Single-sided array of "100uF" ceramic capacitors. The rating is not 100% accurate, since the tolerance on these things is quite large (within 0->-20%)
3) Double-sided array of same capacitors (sealed in epoxy for coolness factor)





Progressively see a reduction in peak ripple voltage. Annoyingly, I only just realised that the first run was in sensored more and the latter two I forgot to plug in the sensor cable :-(

The testing could be a bit more rigorous, but I think is reasonable.

First of all, that's awesome! The cap banks and the scope readouts are great!

It looks like the switching noise gets reduced for sure which is always a good thing, but I don't think that would result in any meaningful impact on performance. I'd like to see a smaller time scale to get a better picture of what's happening between the switching spikes. The first capture is really interesting, it looks like there's a clear 50us period of time where the FETs are switched on and the voltage sags under the load then a clear indication of inductive kickback after the FETs turn off. That's the portion of the signal I would really examine if I had a scope. I'd want to see how far that voltage sags before the FETs turn back off. And I'd also want to see what happens when you run no cap. My gut says the difference I'd see between cap and no cap is orders of magnitude larger than I'd see between any two differently sized caps.

I also think there's zero power contribution from the capacitors - their function is to reduce the noise that affects MOSFET operation. I've got a whole bunch of things I should be doing this weekend, but I'll see if I can get the gear out again.

In the first image, the peak ripple is 228mV. Eyeballing it says the voltage drop is in the hundredths of a volt range. Anyway, I'll certainly post it up if I can find the time.

My reason for building the cap boards was to make something compact and easy to mount without sacrificing anything compared to the standard ones.

That's the same reason I built a ceramic cap bank - space. Made a huge difference in my Mini-B. I was able to tuck the cap neatly between the ESC and receiver in the second pic. Anyway, you don't need to waste your time on my account. You're right, I didn't even think about the vertical scale and how little of a drop that actually was between the spikes. Negligible at best. I think between your scope readouts and the video of the dyno runs, we can safely debunk the notion that caps have any kind of effect on performance.

There is a difference between a basher and a high level racer. A high level racer does feel everything in his car, he is more connected with it.

I'm not going to make any claims of performance, but it comes in many ways. It is well understood (by smarter people than me) that ripple noise has an effect on MOSFET operation/reliability. Do those things translate to better laps times? Like a lot of thing in RC, YMMV and many of us are Ahab on an obsessive hunt for something elusive.

Its more of a time constant applied over the impedance (Zin) of the on-state resistance within the entire circuit.

I always seemed in technique to cap the gates to ground when building a pwm circuit.

Its clear to me how impedance, voltage, existing capacitance, reluctance and time is showing and interacting in the oscilloscope, however I have would been zoomed in looking at the forms and edging, the flora of it all... in-all LoL

Going to throw in one another experiment, since we’re talking about discharge rates and impact to performance. One thing I never understood was why people keep saying that higher amp escs have better acceleration or brakes.

If I were to trust data sheets, even something like a lowly hobby wing stock esc has a pulse load rating of over 300amps. That’s well over the stall current of any reasonable motor, and I can’t imagine how that’d be a limiter to any form of motor braking, whether it be shorting the coils or shunting it back to battery.

so what’s the deal?

Well. I think that has more to do with the internal resistance of the FET's. Low current ESC's have due design and its selling price lower specs FET's with a higher internal resistance. Some FET boards have room to stack 2 or 3 FET's parallel. so you can sell for instance a 35A, 60A and 80A version of a same model. But 3 FET's parallel acting as one will lower the internal resistance like you connect 3 resistors parallel. The more higher current ESC's have with its design and selling price much more room to use much better spec FET's with a much lower internal resistance.

For sure with stock/spec classes people say to use a high current ESC because the lower internal resistance giving much less voltage loss and so less power loss when some current is asked by the motor.

To pressure test the resistance aspect, let's consider a super-old 45 amp hobbywing esc, and consider that a worst-case scenario.
https://www.amainhobbies.com/hobbywi...qztswqlcqxactz

Its resistance is listed as 0.0006 ohms.
Voltage drop = current * resistance, let's assume it's operating at its max 45amp capacity.
Vdrop = 0.0006 * 45 = 0.027 volts

At my club, we charge 2S batteries to 8.4 volts.
0.027 / 8.4 = 0.3%.

So let's say a very expensive ESC can deploy twice the FETs to lower resistance by half.
We'd be talking about a 0.15% improvement.

I seriously don't think human perception feel changes that small. And even if it theoretically does improve lap times, surely there are better ways to chase laptimes per dollar?

Higher rated ESCs usually also have more tuning options for the punch, drive frequency, brake modes etc that changes how the ESC feels. If it feels different, many people will equate that to being stronger. And different braking algorithms can actually improve brake strength without increasing the current capacity.

Totally agree with roelof on this one.



Xtracripsy

No pressure here.

Try not to over think this one young padawan