Why does a brushed motor overheat on 3S?

[CoolRunning]

I know it's 'gearing' ultimately but gearing for what?

For example, I know Slash trucks and lots of RC stuff go fast with brushed motors and they don't necessarily overheat.

I have found this with my totally sock RR10 and SCX10 trucks:

Crawling heats up the motor. The more crawling, the hotter the motors get.

Going as fast as possible and bashing them keeps the motors very cool.

This is in a Melbourne summer where some days it's 37 degrees C and we're out driving around.

So we do some crawling, check the motor temps periodically with our fingers and when they get hot, we zoom around to cool them down.

So, the point of the post.

If I get a 35T motor with say the stock SCX10 gearing (which I think is 87/20) and add a 3S lipo for the extra speed, what will cause the motor to cook?

Is it the crawling or the zooming/bashing at top speed?

I am a bit at an impasse atm as I want them to go faster but lord almighty does brushless cost the earth. ESC, motor, all the upgrade parts which can cost a small fortune, just to make them a bit faster and not cook motors.

I'm wondering if I can keep the above gearing, drop in 3S and simply not crawl them too much/too aggressively to avoid a motor BBQ.

Any help would be greatly appreciated!

 

[WHITE-TRASH]

87/20 is pretty steep for anything on 3s. Your best bet really is brushless. You don't have to go with a crazy high kv which will destroy parts, a 17.5 on 2s is solid all around and won't get hot.

 

[CoolRunning]

I fully understand.

The issue I've found is that even if I don't get a parts destroyer, it's still going to cost me over a few hundred Aussie dollars per truck plus lipos ($350 plus lipos each) for the cheapest Holmes setup.

I naturally will need some beef up parts so it'll get crazy expensive with brushless. I'll easily have like $1100 per car spent when all I really want is some extra pep.

I've tried for hours to pierce together an affordable sensored brushless setup but even basic motors are $110.

I really don't feel they'll make good fast cars anyway due to the locked diffs, high ride height and ESC brake.

I can go 3S brushed for probably $200-250 vs $700.

I'm loving these little trucks as is but a bit more pep would be perfect. I thought about a Yeti or something like a SCT but it would annoy me that it can't crawl or trail as well.

 

[MattySlimz1987]

I fully understand.

The issue I've found is that even if I don't get a parts destroyer, it's still going to cost me over a few hundred Aussie dollars per truck plus lipos ($350 plus lipos each) for the cheapest Holmes setup.

I naturally will need some beef up parts so it'll get crazy expensive with brushless. I'll easily have like $1100 per car spent when all I really want is some extra pep.

I've tried for hours to pierce together an affordable sensored brushless setup but even basic motors are $110.

I really don't feel they'll make good fast cars anyway due to the locked diffs, high ride height and ESC brake.

I can go 3S brushed for probably $200-250 vs $700.

I'm loving these little trucks as is but a bit more pep would be perfect. I thought about a Yeti or something like a SCT but it would annoy me that it can't crawl or trail as well.

If you have the scx10 1 I believe "Hot Racing" makes a 2-speed drop in trans. I considered getting a 1st gen or rtr scx when getting into this hobby and researched it but ultimately got a kit scx10 II. This would probably be the most cost effective way out of getting more wheel- speed out of the thing.You can keep your brushed in there and at the flick of a switch you can have more "pep" for burning up the outback. Man, I bet Australia has some sick terrain out there to really put em to the test! Hope this helps. Cheers mate!
8)

 

[snapon boy]

I use a 12 or a 10t pinnion in all my rc crawlers brushed and brushless on 3s without any heat issues and I'm in west Texas similar conditions temperature wise to Australia I'd guess it's winter here and it's 70f summer 100f plus regularly

 

[slowmethinks]

You can get the HobbyWing Justock 60A ESC and 21T motor for about $100 US. Open up the ESC and Motor and waterproof, done. I have that setup in my sons Bomber and its been doing well for about a month so far.

 

[CarterFab]

87/18 and your heat issues should disappear. Also a good motor does help over cheap machine wound motors.

 

[Hardcoretam]

The reason your motor will be getting hot with crawling is when the motor is under higher load, it pulls more amps and that causes things to heat up a little.
Worn out, dirty or poorly maintained motors also pull more amps so if it's an old motor and getting hot that could be it.
Running them at full speed up and down can cool a lot of motors down on crawlers because they're geared so low the amp draw is very low on flat, even at full speed. Some motors have fans inside them and the high rpm from driving around forces air in to keep them cool.
3s on motors allows them to draw more current than normal so they heat up more. You usually volt up and gear down a bit to compensate.

You could put a heatsink on top of the motor or wire in a small 40mm or similar fan to aim / blow air towards the motor and generate some airflow when crawling but the benefits are negligible.

Gearing down with a smaller pinion will reduce the load on the motor and cause less heat, but doing so is at the cost of top speed.
Higher turns on the motor mean they draw less power (generally speaking) so they also cause less heat, but produce lower raw power and rpm so like gearing, speed suffers.

It's about getting a compromise between motor turns and gearing to get the right power & wheelspeed.

I'm going to be running 13/87 in my SCX10 with a rebuildible 21t brushed motor on 3s and i think it will be just right for me as i mosty do trailing, but if i was always doing rocks where i might get binds i'd change to 35t motor and probably 13t pinion as well (48p gears)

 

[CarterFab]

That's insanely low gearing ^

 

[WHITE-TRASH]

That's insanely low gearing ^

Meh, my rental sporty runs a 35 turn tekin with 12/92 on 4s. That's low gearing. :lol:

 

[ryan_zimmerman]

I know it's 'gearing' ultimately but gearing for what?

For example, I know Slash trucks and lots of RC stuff go fast with brushed motors and they don't necessarily overheat.

I have found this with my totally sock RR10 and SCX10 trucks:

Crawling heats up the motor. The more crawling, the hotter the motors get.

Going as fast as possible and bashing them keeps the motors very cool.

This is in a Melbourne summer where some days it's 37 degrees C and we're out driving around.

So we do some crawling, check the motor temps periodically with our fingers and when they get hot, we zoom around to cool them down.

So, the point of the post.

If I get a 35T motor with say the stock SCX10 gearing (which I think is 87/20) and add a 3S lipo for the extra speed, what will cause the motor to cook?

Is it the crawling or the zooming/bashing at top speed?

I am a bit at an impasse atm as I want them to go faster but lord almighty does brushless cost the earth. ESC, motor, all the upgrade parts which can cost a small fortune, just to make them a bit faster and not cook motors.

I'm wondering if I can keep the above gearing, drop in 3S and simply not crawl them too much/too aggressively to avoid a motor BBQ.

Any help would be greatly appreciated!

I would think it's the weight ratio of the truck is heavier for the motor to push. But since you say it's stock I'm not very sure

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[rngrchad]

I'd say it simply comes to down to the fundamental relationship between voltage, current and resistance in your electrical system.
The greater the Voltage (think 3s greater than 2s) the greater the force being pushed into the esc and motor. If you increase the Voltage, your current goes up if you decrease the voltage the current goes down. IF the voltage is high the current is high, if its low the curernt is low. So the determining factor of what causes your stuff to overheat and motors to fail is simply they become the resistor in the chain of electrical flow and over time they cause a bottleneck of current flow, get hot, draw too many amps because of this and burn up. I think i have it right. The higher quality the brushed motor the less resistance they have to current flow and therefore shouldn't draw as many amps at similar situations so in effect they do as much or more torque with less electrical input as they are more efficient and their electrical efficiency makes them last alot longer. Maybe I'm talking out of my ass. But this is how I understand it.

 

[Hardcoretam]

That's insanely low gearing ^

<iframe width="560" height="315" src="https://www.youtube.com/embed/0yq63T1_h7c?rel=0" frameborder="0" allowfullscreen></iframe>

That's 27t, 2s lipo and 13/87 on 48p gearing
Even though the wheels were ridiciously heavy (10.5oz each front / 6.3oz each rear) the motor was good for doing this all day, but it was quite cold outside.

Wheel speed wasn't great, but 3s would have woke it up.

 

[CarterFab]

That's 27t, 2s lipo and 13/87 on 48p gearing

Even though the wheels were ridiciously heavy (10.5oz each front / 6.3oz each rear) the motor was good for doing this all day, but it was quite cold outside.



Wheel speed wasn't great, but 3s would have woke it up.

That explains why you have it geared so low, wheel weights. Get rid of those and you can run the 87/18 and have same/probably more torque and way more wheel speed, even on 2s.
Wheel weights are the worst thing for a car. Any unnecessary rotating mass robs power, adds lots of strain to the entire drivetrain, and will cause premature failure on shafts, gears, motors and esc.

 

[Hardcoretam]

I was pretty new to crawlers and scalers when i set it up and filmed this.
I still like a little weight in my wheels because most of them are plastic but instead of 10.5oz they're now more like 3.5oz which is probably isn't same as unweighted, alloy 2.2's

Despite the ridiciously heavy wheels, never broke anything, never killed an ESC or motor either but i'm quite a sympathetic driver.

I was in a similar poisition to the OP so instead hoping 21t motor, on 3s and 13/87 will be a good mix of wheel speed and low end control but still to set it up.

 

[EddieO]

That's insanely low gearing ^

A 27t at 13/87 is about right on 3s, I typically advise 12/87 for 27t, 13 or 14/87 for a 30t, and around 17 or 18/87 for a 35t...while you can sometimes bump up a tooth or two, depending on weight.....an 18/87 with a 27t isn't going to last long in many trucks with most drivers...

Later EddieO

 

[EeePee]

The stock, included with the kit gearing on my SCX is 14/87.

 

[CarterFab]

A 27t at 13/87 is about right on 3s, I typically advise 12/87 for 27t, 13 or 14/87 for a 30t, and around 17 or 18/87 for a 35t...while you can sometimes bump up a tooth or two, depending on weight.....an 18/87 with a 27t isn't going to last long in many trucks with most drivers...



Later EddieO

Original post was asking for a 35t motor on 3s. So you agree.

 

[kongluc]

CC sidewinder paired with a trx 21t on 3s is a good start... i run 32p gears 56/11 or 10 not sure it's RRP so it hasn't given me any problems... it's in a slash

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