RC Motor Q&A: Are Motors Always Running at Max Potential? How can they?

[@robaki-dev]

Hi, thanks for the video. I like your reasoning and you’re right, but I think you might be overlooking one thing when designing optimal RPM range for the power sytem - iron losses. In my opinion, targeting 60k mechanical RPM for a power system isn’t (always) optimal. Iron core losses increase exponentially with electrical RPM (eRPM). This means we can’t increase RPM without consequences, even if the motor's physical limits allow it. For a 4-pole BLDC motor, 30k mechanical RPM = 60k eRPM. (number of poles /2 * RPMs) = eRPM So how much eRPM can a motor handle before iron losses become significant? I believe it’s somewhere around 60k eRPM. That’s why manufacturers typically pair 3000KV 4-pole motors with 3S LiPo batteries and target max 30k mechanical RPM (60k eRPM). I don’t entirely buy the explanation that manufacturers simply have an excess of 3000KV motors lying around. :) Maybe you could compare the performance of the two systems on the dyno? If we use a 2-pole 3650 motor in a 1/10th scale RC car and aim for 60k max RPM/eRPM, it becomes impractical to design a drivetrain with such a high gear reduction while maintaining a reasonable wheel speed. I recommend the article "Choosing the Right BLDC Motor and Battery Setup for an Electric Skateboard" from Benjamin Vedder's blog - the author of the VESC project. Keep up the great work educating others about RC tech!

[@alexandermcalpine]

Excellent Post!

[@RCexplained]

Thanks for the comment.

[@2down4up]

Took my Traxxas Hoss, now the “new” stampede 4x4 VXL, and took out the 3s ESC and dropped in the 4s from the Max. Absurdly overpowered! Absurdly fun!

[@RCexplained]

Love it!

[@ullmastarenopenings9763]

Thank you for the thorough answer! I do understand now, and it will help me a lot with my builds! As you probably understand, I don't like to take statements as fact, without an explaination how. Conversation is necessary for true understanding. Thank you! 🤝

[@jparker785]

Comparing to internal combustion engines, and racing, is perfect. You have to match components for what you intend to do with the vehicle. Learning spec sheets is very good, too! The math is simple when you grasp it. Keep the vids coming 😊✌️

[@RCexplained]

I'll keep them coming! Thanks for your comment! 😊

[@brandongollach]

I use tires as my gearbox

[@RCexplained]

Haha, well done

[@brandongollach]

@RCexplained i have a wltoys 12th scale with a 3660 3500kv stock gearing and my personal best is 79mph with 80mm tires it might sound crazy but with my 65mm i run around 60ish so theoretically ill need 100mm+ to go 100mph

[@RCexplained]

@brandongollach no doubt. Overall tire size makes a significant difference.

[@fromthebackofmymind]

NITRO Drag cars rely on tire growth for top speed.

[@zid_just_zid]

Very useful to see explanations of how some of this stuff works. I found your channel when trying to figure out kind of the opposite of optimizing/speed running -> scale driving. My limited understanding of things tells me that to get scale style performance one would want to be able to limit max current draw(torque/acceleration) and max rpm(top speed). Am i off or on target with this and do you know if there are readily accessible ESCs that allow for adjusting these parameters (probably down by a lot) to mimic scale, rather than to target speed?

[@RCexplained]

All you would need to do really is select your power system and gearing to match the top speed you'd like to achieve.

[@surfside75]

I keep it simple, overpower the motor with bigger esc and batteries⚠️😁

[@RCexplained]

I understand what you mean it's a good approach

[@DanielK-xn5si]

I like your in depth explanations and altgough factual I feel they are somewhat biased. Why always push high KV motors as appearing to put out more watts etc when you are varying the current but not the voltage? If I run a motor half the Kv but double the volts I have similar watts, similar max rpm but cooler running temperatures. A more specific example I would like to know is take for example the hobbywing motors, you have the 56113 at 800kv or even 1100kv and the larger 70125 at 560kv..most people tend to opt for the higher Kv smaller cans as they are limited up to 12s in most cases but im wondering even though the 560kv is potentially over 16s capable even on 12s being a larger can size and being almost 2kg vs 1.2kg with similar motor construction (same product family) shouldnt the larger lower Kv motor be able to handle way more current and be geared much more aggressively making use of its torque to create an overall faster vehicle? I dont see a reason why a manufacturer would bring out a larger heavier motor of lower Kv in the same product line and for the same scale of vehicle for it to offer less performance and both are limited to the brands 12s escs? If both can be run max 12s on the brands on escs why would when choose the larger lower Kv can over the smaller higher Kv can if both cans are aimed at the 1/5 scale market?

[@RCexplained]

The video these questions come from literally show a high and low kv motor producing the same total wattage. This image was on the screen for most of the length of this video.

[@MangoJim90]

🥳👍👍💯

[@fromthebackofmymind]

Peak power just before motor failure?

[@fromthebackofmymind]

741 watts is 1 hp.

[@fromthebackofmymind]

Clamp an ammeter on the motor wire from the esc. Scale down a hobby Dyno for max power under load.

[@fromthebackofmymind]

Get two bakers ball bearing rolling pins. Align them in a diy jig to make a chassis roller dyno.strap car down with Bungees. Gear a dc motor to the pin and wire in a dc voltmeter and series ammeter for power measurements.

[@ruuster83]

electric motors are way better than IC. can't wait to get an EV.

[@BUILDEMTORIDE]

That's a troll post if I've ever seen one.... good luck!!

[@ruuster83]

@@BUILDEMTORIDE gas is 10 cents a mile. ev is 3 cents a mile. ymmv

[@rtz549]

Bolts are real cheap now. And Leafs.

[@BUILDEMTORIDE]

@ruuster83 ev has its place, but making mandatory ev goals and laws is asinine, when the grid capacity is multiple decades past that goal. We also don't produce enough "clean" energy to justify moving your tailpipe to the electrical plant and expecting fewer emissions. As well as other countries offset any real progress, we are a drop in the bucket on the entire planets pollution scale.

[@ruuster83]

@BUILDEMTORIDE so this makes me want to pay 100$/ month for gas when I can charge at home for $25/month? Also how could a car possibly out perform a Power plant emissions wise? Many small engines are much worse than one big engine. EVs are 80%+ efficient and IC cars are 25% thermal efficiency. This isn't news.