Have tech questions? Will answer.

[westerlycarrot9]

Good evening people. I'm trying to understand how the Amps of an ESC can affect the performance (speed, torque etc) of an rc car combined with the specs of the motor and the battery.

 

[durok]

Update, i had some time this weekend, and tore the rig down for maintenance.

I found a drive shaft set screw rubbing the transmission case, thus the surging! I guess the power of the trail master overwhelmed it in normal power, but not going downhill and on the flats.
Lesson learned always check mechanical before blaming electronics....

Thanks for posting this update - it's always useful to hear what the end cause was of particular problems, especially when they aren't necessarily common!

"thumbsup"

 

[Voodoobrew]

Good evening people. I'm trying to understand how the Amps of an ESC can affect the performance (speed, torque etc) of an rc car combined with the specs of the motor and the battery.

Think of the amp limit like a fuse, if you exceed it, it can burn up. And it's not easy to find out how many amps you have, the battery amps is not the amps the esc is talking about.

But Basicaly if your amps are high, your electronics will probably be hot, if they are not hot, then you are probably fine.

But it's much more complicated than that. You can pick the motor and the voltage. That combination determines your amp draw for the most part. The battery does not determine the amp draw so much as it facilitates and allows the amp draw.



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[Voodoobrew]

Good evening people. I'm trying to understand how the Amps of an ESC can affect the performance (speed, torque etc) of an rc car combined with the specs of the motor and the battery.

Another point, two main ways to increase amperage are as follows.

You can get a faster motor of the same size by getting a lower turn motor. (you can also convert this speed into torque by gearing down.

Or you can get a higher torque motor of the same speed by getting a larger motor.

More amps means more power,
Power can be speed or torque or both, it can also just be more heat but let's ignore that for simplicity.

Now since our motors have more power and thus a higher amp draw, our battery will not last as long and our runtime will be reduced.

Another way to increase amp draw is by increasing the battery voltage. Doubling your voltage will double your torque, speed and amp draw.



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[westerlycarrot9]

Another point, two main ways to increase amperage are as follows.

You can get a faster motor of the same size by getting a lower turn motor. (you can also convert this speed into torque by gearing down.

Or you can get a higher torque motor of the same speed by getting a larger motor.

More amps means more power,
Power can be speed or torque or both, it can also just be more heat but let's ignore that for simplicity.

Now since our motors have more power and thus a higher amp draw, our battery will not last as long and our runtime will be reduced.

Another way to increase amp draw is by increasing the battery voltage. Doubling your voltage will double your torque, speed and amp draw.



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So basically if i want better performance whether that means speed or torque i should mess around with amperage and amperage draw right? I know about gearing because i've already done that part to my TRX4..changed to a 9T pinion gear I'm planning to start a touring car project and obviously i'd like to make it as fast as its chassis will allow it to be so i'm looking for ways to do that besides gearing. When you say "More amps mean more power" you mean the ESC's amps right? What about the C discharge rate on LiPo batteries? Is this a contributing factor as well?

 

[Voodoobrew]

When you say "More amps mean more power" you mean the ESC's amps right? What about the C discharge rate on LiPo batteries? Is this a contributing factor as well?

No, neither battery c rating or esc change amps. (they do slightly because quality matters but for simplicity no)

Battery voltage and motor turns change amps.


You don't change amps. You change the motor to one that draws more power. The amps changing is a side affect.

Adding amps is not really a thing.

An esc or a battery with a higher amp "rating" means it can handle a more powerful motor with out burning up.

So you have a motor that draws 40 amps. If you have a 60amp esc and upgrade to a 120amp esc, you end up with less money. That's it.

But if you have a 40 amp motor and a 30 amp esc. The esc will burn up.

Motor manufactures don't tell you the motors amp draw because it varies with voltage and resistance. They could tell you the maximum amp draw at 6volts is 40amps. So a 60amp esc would be ok? It is at 6v, but if you go to 12v batteries you just turned that 40amp motor into an 80amp motor and the esc's amp rating is still at 60, so the esc burns up.


A higher 120 amp esc is twice as hard to burn up as a 60 amp might be a simple way of stating it?

Same with batteries a higher c rating has less chance of overheating and exploding.

You may want to youtube basic electronics and ohms law. I might not be explaining it clearly.

I am probably over complicating it.
But but we generally don't think about adding amps in rc. We add voltage, or a more powerful motor. This causes the amps to increase. And the battery's c rating (amp draw rating) (not to be confused with amp capacity rating ex 2700mAh) and esc amp rating must be higher then the amp draw of the motor at a peticular voltage. Or they burn up.






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[Voodoobrew]

So basically if i want better performance whether that means speed or torque i should mess around with amperage and amperage draw right?

Yes and no.
You're not wrong per say, but your not wording it right. Let me try to reword it for you.

So basically if i want better performance whether that means speed or torque i should mess around with motors and this will change my amperage draw and performance right?

Or

So basically if i want better performance whether that means speed or torque i should mess around with voltage and this will change my amperage draw and performance right?



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[Voodoobrew]

Also if we have an rc dragster.
That is all about fast takeoff.
Telling the dragster to go from 0 to 60mph in 1 second requires a massive amount of amps (let's say 200 amps).
But driving a quarter mile at 60mph may only have an amp draw of 25amps.

So in the case of a dragster and the short amp burst. A low c rating cannot supply enough power, so the dragster starts slow, or the esc glitches out, or the battery over heats.

It's not that higher c rating makes you start faster, it's that too low of a c rating is inefficent and potential dangerous.

So our 200 amp dragster has a 2000mah 10c battery. This means the battery is rated to allow for 20 amps. The dragster will start slow and never get to 60 mph. The battery will get damaged, hot and unsafe.

Again with a 200 amp dragster that has a 2000mah 50c (that's 100 amps) the dragster will start kinda slow and will eventually get to 60mph, the battery is working beyond its safety limits, and is probably getting hot. This will cause damage to battery, and reduce the overall life of the battery.

Again with a 200 amp dragster that has a 2000mah 100c (that's 200 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. But we are pushing the battery to its limit, it may still be warm. Probably No damage to battery

Again with a 200 amp dragster that has a 2000mah 200c (that's 400 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. But now the battery is well in its safe range. No damage to battery

Again with a 200 amp dragster that has a 2000mah 1000c (that's 2000 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. Zero performance increase over 100c rating. But easy for battery to handle. No damage to battery

So you will only see a performance gain if the battery you have is being pushed beyond its c rating. (again there are performance gains but for simplicity sake, it's pretty minor gains)


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[JohnRobHolmes]

I'll sum it up, lol! The motor speed, size, gearing, and voltage being run will determine the amperage needs. In a crawler, you can basically just use about any 1/10th scale ESC and be fine since the rig gearing is so slow compared to other segments of the hobby. If it isn't running hot, there is no issue.

 

[westerlycarrot9]

Also if we have an rc dragster.
That is all about fast takeoff.
Telling the dragster to go from 0 to 60mph in 1 second requires a massive amount of amps (let's say 200 amps).
But driving a quarter mile at 60mph may only have an amp draw of 25amps.

So in the case of a dragster and the short amp burst. A low c rating cannot supply enough power, so the dragster starts slow, or the esc glitches out, or the battery over heats.

It's not that higher c rating makes you start faster, it's that too low of a c rating is inefficent and potential dangerous.

So our 200 amp dragster has a 2000mah 10c battery. This means the battery is rated to allow for 20 amps. The dragster will start slow and never get to 60 mph. The battery will get damaged, hot and unsafe.

Again with a 200 amp dragster that has a 2000mah 50c (that's 100 amps) the dragster will start kinda slow and will eventually get to 60mph, the battery is working beyond its safety limits, and is probably getting hot. This will cause damage to battery, and reduce the overall life of the battery.

Again with a 200 amp dragster that has a 2000mah 100c (that's 200 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. But we are pushing the battery to its limit, it may still be warm. Probably No damage to battery

Again with a 200 amp dragster that has a 2000mah 200c (that's 400 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. But now the battery is well in its safe range. No damage to battery

Again with a 200 amp dragster that has a 2000mah 1000c (that's 2000 amp rating). The dragster takes off at full speed and reaches 60mph at minimal time. Zero performance increase over 100c rating. But easy for battery to handle. No damage to battery

So you will only see a performance gain if the battery you have is being pushed beyond its c rating. (again there are performance gains but for simplicity sake, it's pretty minor gains)


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First off thanks for taking the time to write down so many things! Especially that last part with the RC dragster example was really educational about the C rating of LiPo batteries. For example i use a 2S 3500mAh 20C battery for my TRX4. The truck is a slow crawler so a 20C discharge rating should be fine since i don't need any fast startups right?

Concerning the motor and ESC stuff, right now i'm using a HW 1080 which is an 80A ESC and an RC4WD 35T Crawler Motor whose specs i just paid real attention to after reading through your replies :lmao: At 7.2V (no load) it draws 1.25A and at 7.2V (max. efficiency) it draws 4.62A. So even if i use a 3S LiPo which if i'm correct is a 11.1V battery, the 80A ESC can still work without any problems. The 55T version of the same motor draws less Amps, specifically 0,75A at no load and 3.35A at max. efficiancy, which seems to be the reason why higher turn brushed motors produce more torque! And then for example a Tamiya RS-540 Sport Tuned Motor 23T which is a faster one draws 12A at 7.2V (max efficiency). However this particular motor's specs say that it can be used at 6V up to 8.4V so my question is which kind of voltage is this one? I mean the only other place on an RC where these kinds of voltage numbers are present is the steering servo.

So basically if i want to start building a new kit (which i do actually xD) i should first choose a motor, then a battery and then an ESC that can handle those two without any issues right?

 

[Voodoobrew]

At 7.2V (no load) it draws 1.25A and at 7.2V (max. efficiency) it draws 4.62A. So even if i use a 3S LiPo which if i'm correct is a 11.1V battery, the 80A ESC can still work without any problems. The 55T version of the same motor draws less Amps, specifically 0,75A at no load and 3.35A at max. efficiancy,

But the max load amperage is not listed. Max load would be when a wheel is bound up and can't turn but you apply power. Your 0.75A motor is probably over 100A if you power it when the wheels are locked. The amp draw of the motor is not constant. It increases as you increase load to the motor, like having a heavier rig.

You don't really need to think about it all that much. Basicaly if you want more power get a bigger or lower turn motor. If you have the trx4 sport you can get a 45t spur also.

Brushless motors offer more torque and speed as well. The Puller pro is pretty good if it's within your price range. I like the 2200kv on 4s. Then I gear it down.

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[westerlycarrot9]

But the max load amperage is not listed. Max load would be when a wheel is bound up and can't turn but you apply power. Your 0.75A motor is probably over 100A if you power it when the wheels are locked. The amp draw of the motor is not constant. It increases as you increase load to the motor, like having a heavier rig.

You don't really need to think about it all that much. Basicaly if you want more power get a bigger or lower turn motor. If you have the trx4 sport you can get a 45t spur also.

Brushless motors offer more torque and speed as well. The Puller pro is pretty good if it's within your price range. I like the 2200kv on 4s. Then I gear it down.

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That's right! Is there a way to calculate something like that? Well i'd like to dive deep into that stuff in order to know exactly what i'm getting when buying electronics and how to better pair a motor with an esc etc. Hmm i can understand brushless motors being able to produce more speed but torque too? I suppose that KV doesn't stand for kilovolts right?

 

[durok]

That's right! Is there a way to calculate something like that? Well i'd like to dive deep into that stuff in order to know exactly what i'm getting when buying electronics and how to better pair a motor with an esc etc. Hmm i can understand brushless motors being able to produce more speed but torque too? I suppose that KV doesn't stand for kilovolts right?

https://www.motionrc.com/blogs/motion-rc-blog/understanding-brushless-rc-motor-specifications

 

[svt923]

Hmm i can understand brushless motors being able to produce more speed but torque too?

And some brushless motors make a lot more torque. For example, the Revolver makes like 3 times the torque of a 35T Trailmaster and that was all the dyno could measure before the belt started skipping.

Hopefully JRH chimes in with some of his dyno charts.

 

[Voodoobrew]

That's right! Is there a way to calculate something like that? Well i'd like to dive deep into that stuff in order to know exactly what i'm getting when buying electronics and how to better pair a motor with an esc etc. Hmm i can understand brushless motors being able to produce more speed but torque too? I suppose that KV doesn't stand for kilovolts right?

If the manifacture dosent Gove it to you then you would get it by testing. Basicaly by locking the armature in place and mashing the throttle for a split second and measuring the amp draw. The mamba x and other logging esc's can tell you your amp draw over time also. The hobbywing 1080 dosent log the information.

The amp ratings on the esc and battery are not hard ratings either. Most of the time your probably under 20 amps, but on the 80A hw 1080 if it spikes to 120A for a second your probably fine, the number is more of a guideline then a hard rule.

From rotor drone. Com
Answer: “Kv” refers to the constant velocity of a*motor*(not to be confused with “kV,” the abbreviation for*kilovolt). It is measured by the number of revolutions per minute (rpm) that a*motor*turns when 1V (one volt) is applied with no load attached to that*motor.

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[Voodoobrew]

I run a hand wound 550 crawlmaster 10t motor which is a very powerful motor on my hw 1080, it's a 10lb rig on 2.2 tires. I reduced the acceleration or punch in the esc to 4 so it starts slower on a drag race. I have a 96t spur and a 9t pinion with a wraith transmission and scx10 2 axles so it's geared pretty low. The esc takes it like a champ and stays cool.

You don't need that punch. Real crawlers don't have it. It's just for fun an breaking stuff.

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[strap624]

How does a 540 magnum compare to a 550 crawlmaster pro?

 

[Voodoobrew]

The magnums have a bigger armature than the 550, so more torque, slightly higher minum startup speed I believe. Magnum is also a smaller can, so it fits anything that uses a 540 motor.

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[strap624]

Thanks, there's very little info on the magnums, aside from a coulple Holmes videos on YouTube. Couldn't find any real running videos of one in action showing a slow start/crawl. I'm kind of still torn between a revolver or a magnum. Possibly just a regular crawlmaster 550 pro .Couple guys I run with have the revolvers and they are cool .

 

[Thloftus]

As far as the ESC goes, the Mamba X for sensored is the best available IMO.
If you were looking at a Revolver or other sensorless motor, then yes the SW4 would probably be the better choice for 2/3s use.
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What he said. I would choose a standard over a stubby for a bigger rig. They run cooler.

Thank you for the feedback! I ended up going with a 1400 kV Revolver + SW4. Should be here Tuesday. Looking forward to trying my first outrunner!


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