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ThunderDragonCy

Hot 3650 motor in SCT - Do I need a 540 for the torque?

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Bit of advice please. When I built my Turnigy short course truck I used a spares box Trackstar 4370kv sensorless ESC and motor combo I acquired in a used buggy. Now the truck seems plenty fast enough and I don't seem to be getting any thermal shutdowns but the motor is getting REALLY hot. The gearing is pretty low at 12 FDR even for a truck. The motor is one of those typical Chinese finned body jobs so I am guessing it's one of the 380 rotors in a big can? Is it just struggling to drag a 2kg+ truck about? Bit lacking in torque so heating up?

Any good advice? Do I need to get a 540 motor? Or a 550? I have no idea about motors beyond standard 540 tamiya size. Maybe a brushed combo would be good? Lacks torque though but plenty of RTR trucks seem to come brushed. Thanks! 

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A full 540 would probably be better. The finned ones are good but have their limits and 4370KV is pretty high, I tend to stay closer to 3300 when I use them in bigger stuff.

You could try the gearing, I know people have run the SCT on lower KV versions of those motors and had good results. A brushed of equivalent RPM would probably run as hot if not hotter than the even the finned 390. Best choice if you need to maintain your current speed and run cooler would be a full size 540 or 550. If you could lose a little top end then playing with the gearing could be the easiest way to cool it down.

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Is it 2wd or 4wd?  I know at our club the 2wd SCT guys run into heat problems with 540 sized motors and they go through motors reasonably often, as in most would be changing each season vs a few seasons for a buggy.  I think they run 10.5T blinky so they will be geared pretty aggressively too.

4wd SCT is all but dead at our club but there was talk of allowing them to run the 8th scale motors and 4S batteries as a big problem with 4wd SCT is the strain on the 10th scale electronics, they just aren't up to it when geared for racing.

Trackstar make a brushless in 550 sized for SCT but Hobbyking only have low turn motors available.  In saying that the one linked below is "only" (yep looking at you Jason!) 4550kv and its 4.5T so maybe the lower turn are the way to go?  That I don't know.

https://hobbyking.com/en_us/turnigy-trackstar-sct-4-5t-sensored-brushless-motor-4550kv-550-size.html?___store=en_us

As a basher I would probably go for a 550 sized with closer to 3000kv than 4300 kv, or even pick up a cheap 8th scale motor as they have more torque and it won't be as stressed.  The 8th scale usually run around 1900kv - 2200kv and 4S batteries, so maybe run it with 3S (as I doubt the Turnigy SCT will be as durable as a race kit so 4S could be overkill).
 

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Cheers fellas. Sounds just as I thought. I don't really want to go to the expense of 3s or 4s batteries and some big ESC for a park basher. I would quite happily reduce the top speed too, so it sounds like my favourite speed passion 13.5 3300kv motor and the 120 amp ESC I like is the go to. I'll rob a set out of one of my other cars and see how it goes. I prefer the smoother sensored control anyway. 

Cheers! 

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I have a Serpent sct 2wd, I Have a hobbywing quicrun 3654 3800kv in it, that runs cool but thats onroad, the 380 motors do not have enough torque, even a normal 540 motor  can struggle, if its me I would buy something like a hobbywing 3660 motor to be safe certainly if you run it offroad, I am going to change the motor for the 3660 can lenght, because I am going to drive the car offroad to.

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38 minutes ago, ThunderDragonCy said:

Cheers fellas. Sounds just as I thought. I don't really want to go to the expense of 3s or 4s batteries and some big ESC for a park basher. I would quite happily reduce the top speed too, so it sounds like my favourite speed passion 13.5 3300kv motor and the 120 amp ESC I like is the go to. I'll rob a set out of one of my other cars and see how it goes. I prefer the smoother sensored control anyway. 

Cheers! 

I think that would be a better choice. I have no racing experience so can only speak from my bashing experience but I have a full size 3900KV in my Hunqai Slash 4x4 clone and feels like a good match, it can get fairly warm when I used it on 2s off road for extended periods. On road it's much cooler and I can run 3s.

I believe the genuine slash 4x4 brushless has a 3500KV 3650 motor and is rated 2-3s.

I've run those finned motors in fairly big vehicles such as a TL-01B monster truck at 3300KV and it was honestly fine but the higher in KV you go, the hotter they get just like any motor and they run comparatively hotter than a full 540 all else being equal. I found 3000-3300 to be about the limit for a 4x4 1/10 truck. I've actually even run one in an 8th scale truck and it did ok but I wouldn't use that setup every day!
 


The highest KV finned motor I'm currently running in a truck is a 3900KV in my heavy dump truck but despite the name, that's actually quite a small truck so it works ok.

The price difference between a finned 380 and a full 540 or 550 is so small these days there's really no point getting the finned one looking forwards unless you have a application where it's more suitable. For me this usually involves older vehicles with dubious gear strength and/or handling qualities. The finned motor gives me some of the brushless benefits such as good performance, usually cooler running vs a brushed motor even though they have a 380 core, low maintenance and better run times but at the same time, the slightly lower power vs a full size 540 brushless can make things easier on the drive train and be less likely to overwhelm a primitive chassis.

It might be worth getting a temp gun too, opinions vary but around 160-180f seems to be considered the very highest temp that's still safe. Most people are unable to keep their finger on a motor that is even 120f/50c

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Does it have bigger tires?  (You said FDR 12, so tire size must have been considered already)  Running that hot, even for a 390 motor is rather surprising.  I wonder some cogging could have caused the extra heat?  

Neodymium magnets (used in the core of brushless motors) are one of the strongest magnets.  But it loses a lot of power when heated.  I would think a 540 sized motor would run cool.  If not, FDR of 15 or 16 could solve the problem even with a 390 sized motor. 

DF03 weighs 1.1kg.  390 sized motor would do okay for DF03, but perhaps 2+ kg might have been pushing it a bit.  

 

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@nowinaminute I have been noticing the RTRs come with mid 3000s kv. To be honest I am not really getting any obvious performance issues but it is quite hard to drive on loose surface because of the lack of low speed throttle control and all the torque flooding. I am not at all married to this level of power or motor format. They were literally what was spare when I built the truck. I also don't want to burn out this setup then have to buy something else. Would rather sell it running nicely (which it is) and fund something more suitable. I have seen some Racestar 3300kv 540 size sensorless motors for under 20 quid so I might get one of those and plug it in to the existing ESC.

@Juggular Yes, standard SCT wheels have mostly 3" rims and fairly tall tyres, plus they are effectively 1/8th scale in terms of size even though everyone calls them 10th. Certainly the chassis is broadly similar to my TRF201 but its much wider and 50mm longer wheelbase. With the big shell as well its a pretty heavy vessel. When I had the same motor in my TRF201 I was running fdr under 9 with no issues at all, but that buggy feels like half the weight of the truck! 

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I have a Losi XXX-SCT running on an 11.5t Novak Ballistic motor, somewhere around 3800kv. It barely gets warm. I'm messing with the gearing now because I can, but it's at a good speed so I may leave it as is. A 540 will run it no problem once you get it geared properly.

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How about a low cost sensored brushless set up? The Trackstar Stock ESC is excellent, although you'll need the program card, and a 13.5 or so will shove a 2WD SCT around nicely with nice linear power. Sensored brushless is so nice to drive that you'll never want a sensorless system again.

I've never had one of those finned can motors, and they seem to be more difficult to find than they were a few years ago. I'd really like them in a 2 pole sensored version for vintage or fun use, where the lower torque/higher RPM would better suit the chassis.

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2 hours ago, Big Jon said:

How about a low cost sensored brushless set up? The Trackstar Stock ESC is excellent, although you'll need the program card, and a 13.5 or so will shove a 2WD SCT around nicely with nice linear power. Sensored brushless is so nice to drive that you'll never want a sensorless system again.

I've never had one of those finned can motors, and they seem to be more difficult to find than they were a few years ago. I'd really like them in a 2 pole sensored version for vintage or fun use, where the lower torque/higher RPM would better suit the chassis.

Totally agree. This is the only sensorless system I own. All my others are sensored. I have ordered a cheap 13.5 3100kv 540 size motor to hook up to a spare tamiya tble02s ESC. 

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Hey ThunderDragon,

I have a couple of new in box Atomic 550 sensored motors.  I picked them up directly from Atomic one Black Friday but I haven't had a need for them since.  I'd be happy to let you have one for $30 +S&H if you'd like.  PM me if you're interested and I'll take some pics for you.

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