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Brushless car vs. boat motors - make me smart!

Old 03-20-2021, 07:59 PM
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Default Brushless car vs. boat motors - make me smart!

Hi all, can someone help me understand the differences between brushless motors and esc's that are spec's for cars vs boats, and how interchangeable they are (specifically boat to car)?

A little background, until last Christmas, I hadn't touched an RC since about 1986, but I picked up a couple little RTRs to play with my 10 year old and immediately started planning to upgrade one to teach him some diy skills. One thing led to another and I decided it would be better to build a car that we could take to our local weekend track days and I ended up with an LC buggy kit.. Local rules cap motor kv at 3500 but don't specify anything else. The LC takes a 2838/2850 motor, but I'm wondering if it's worth shoehorning a 2958 boat motor in for a little extra torque? (Short term driving skill limitations aside of course!)

Would the boat motor have cooling problems?
Is there some functional difference that would make the boat motor unacceptable for a car?
The boat specific esc's in the motor/esc combos I've seen appear to be physically different than car specific esc's. Would that piece be car-comcar-compatible?

Thanks and sorry for the new question. I haven't been able to find an answer by searching and I've been trying for days.
Old 04-04-2021, 08:08 PM
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BKoz559
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In a short answer the motors are built on the same basic principals and basically operate the same. However, the number of slots in the stator and number of poles on the rotor will usually differ, meaning different KV ratings and different power ratings. Most motors for 1/10 buggies operate in the low 2000 - 4000KV range. I do own a couple boats but I'm not as familiar with all of the options that are available. What I do know is that marine motors are built (typically) with lower KV ratings and generally higher torque output. As long as you can bolt up a motor to the buggy's motor mount and get a pinion gear on it then it will run your car. From there you will need to figure out a gear ratio that works and supply adequate power to it. You would generally run 2S LiPo batteries on a 1/10 buggy, but some marine applications can run 6S or even 8S. The guys on YouTube making speed run cars typically use airplane or helicopter motor systems adapted to fit into a surface vehicle and power it with multiple LiPo packs in series.

A marine ESC will operate a marine motor but may not operate the buggy motor because of the difference in designs for the 2 types of motors. The marine ESCs pulse timing may not line up very well with the rotation of the surface motor, or vice-versa. I'm not saying no way no how but you could very likely run into an issue there. At the very least I would expect a fair amount of cogging at startup. If you run a marine motor then use a marine ESC, but you won't have brake or reverse control.

In the end, they make these different systems specific for their applications because each application has specific needs and require different types of power and or control. If you don't already have a motor system for your buggy I strongly encourage you to purchase a surface brushless system for 1/10 vehicles.

Last edited by BKoz559; 04-04-2021 at 08:11 PM.
Old 04-10-2021, 09:11 PM
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Thanks for the response. This is more of a learning experience than anything right now and I appreciate the guidance. So the motor that got me thinking (just something that popped up on ebay. not even sure I saved it) was a 4pole, just under 3500 KV unit. I have no idea on the number of slots in the stator for either a typical buggy motor or the boat motor. Is it the stator design that impacts the pulse timing on the ESC, or is there something else to consider?
Also as long as I'm asking, I found the oddball size boat motor (was the only 29mm can I've seen). While I was looking for a breakdown of available motor sizes. Any chance there a chart or list of motor series and sizes floating around anywhere?

​​​​​​THanks!
Old 04-11-2021, 10:50 AM
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The stator design can vary depending on what the motor is intended for, meaning 1/10 2wd or 1/8 4wd off road for example. The basic setup is 2 or 4-pole rotor with 6 slots around the can. Basically each phase has 2 windings but, in the case of airplane motors the stator is divided up into smaller sections in multiples of 3. Say 18 total or 6 windings per phase. They can also be "slotless" as well. There are many ways they can be built.

Depending on the design of the motor and the ESC you run it from there might be some compatibility issues. The ESC will still create the rotating flux field electronically but the motor may cog if the number of sections / poles doesn't sync up well with the ESCs rotation as it's running. You'll find forums of guys asking about why their Castle motor doesn't run as fast as their stock Traxxas motor with the same ESC even though the KV rating was higher. It turned the motor but there were some timing issues and in the end the motor ran slower. The Traxxas motor may be slotless also because when you roll that motor by hand the rotor doesn't jump between the slots of the stator. It's a fluid motion so I'm assuming it's slotless. Someone can verify this independently. If you get a system then of course it's designed to work together. For the most part you probably won't have issues when intermixing brands but it can happen.

You might be able to find some chart or other reference for the sizes. I don't know off hand.
Old 04-30-2021, 06:41 PM
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hi [email protected] to help you a little some math with brushless motors , with KV KV X 1 VOLT = RPM 2850 KV X LIPO 2 S BATT 7.4 VOLTS = 21,090 rpm the , 3500 kv motor x 7.4 v = 25,900 rpm the 2850 kv rated motor is equal to a 17.5 turn motor brushed motor , the 3500 kv is equal to a faster 13.5 turn brushed motor , most tracks have a motor rated class 1/10 scale 2 wd buggy 17.5 turn motor and modified class any turn motor 6.5t that you ca handle LOL , 4wd buggy class 13.5 t motor and modified class any low turn motor yes they equal the playing field now, and your driving skills and set ups come into play, shock oils springs wheels and tires type tire alignment , chassis height track type hard clay , loose dirt , astro turff ok
you have to set up the right gearing for the spur gear and motor pinion gear , so you do not cook ( burn up the motor or speed control ) i use a hobbywing esc 120A it will handle down to a 4.5 turn motor with a 2 s lipo battery go on you tube and see some of the rc racers
set ups , team associated b6.1 ,6.2 4wd b64 b74 xray xb2 , xb 4 losi 22 , 22x4 , schumacher buggies tekno buggies 4wd also some of the motors and speed controls are sensor , non sensor motors cog at start and when speeding up ok
well i hope i helped you a little mugey
Old 05-08-2021, 03:39 PM
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Hey, thanks for the advice guys, and sorry for slow responses on my part (did I mention newborn and demanding work schedule? Well, add buying a new house and moving into the mix! &#128563. Anyway, I've done enough research to have a basic handle on the general concepts... Enough to be dangerous anyway which is why I'm asking questions.

So for the KV rating my understanding is that the lower of motors are generally more torquey and can be geared up to compensate, right? So how do you select the right gearing? Just do temp checks on motor and ESC occasionally? What's a safe max temp?

For my original question about can size, that was also because my understanding is that larger dia yields greater torque for the same KV rating... So in theory running a larger diameter would allow for higher gearing right?

Our local hobby store cancelled the 2021 season, but the "track" is just a handful of cones and wooden ramps in the back lot of the local home depot so it's subject to change and I'm assuming the competitive drivers are changing setups based on the configuration of the day. Either way, we have time to figure things out before it really matters at least.

Thanks again!

Last edited by [email protected]; 05-08-2021 at 03:42 PM.
Old 05-08-2021, 04:54 PM
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You should select the KV rating for the type of driving you're doing, that's after you've chosen the size of motor you need based on the vehicle you're driving. 1/10 scale motors are 36mm diameter cans, 1/8 scale are 40mm, 1/5 scale I believe are in the mid to upper 50mm range; I believe 57mm?

So, if you're going to race a 1/10 2wd short course truck then you're looking at a 36x50 or 36x60mm can. These are pretty standard so anything on the market intended for 1/10 scale vehicles will be those dimensions. If you were running a 4wd 1/10 then it would be a "short course" motor which is the same diameter at 36mm but they're around 65-70mm long.

Honestly, you don't need to get that technical about it unless you're trying to custom build a specific vehicle for another purpose; like a dedicated speed run machine or something else extreme. Based on the vehicle you intend to use you would search for a brushless system that is intended for a vehicle that size. Also, sensored systems are much preferred in racing versus unsensored motors. In organized racing the club may have certain requirements regarding the type of motor system they will allow you to run. Check for any of those rules at your track. If it's just buddies having fun then I guess anything goes.

Back to KV ratings, it also depends on the vehicle and track conditions. For most 2wd racing I would suggest no higher than 3500KV. You generally see low 2000s up to low 3000s on the tracks running 2S LiPo batteries. 4wd SC motors can start in the mid 2000s and run up to 4000 or so KV, again on 2S. Going above 4000s in racing environments is not advisable and again, tracks may have rules in place too. The 5000+KV systems you see available are best suited for open spaces and bashing. You wouldn't fare well on a track with such a high RPM motor unless your track has long stretches and big sweeping turns.
Old 05-09-2021, 05:03 AM
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hi @ 9000 and BKoz559 well glad we helped stay with the 36mm dia can motor stay with the motors around 2500 to 2850 kv which is probably around 13t turn motor you will need to gear it properly
due to weight of buggy , run time , track , add a fan to cooling motor , temps should be no higher than 170 . i never heard about a LC BUGGY KIT , mostly the race buggys , truggys TEAM ASSOCIATED , LOSI , XRAY, TEKNO , SHAUMACHER , KYOSHO these are some of the best on the planet for racing and bashing, see the youtube videos on this stuff for set ups motors gearing racing for 2wd and 4wd your
buggy has a internal gear ratio divide pinion into spur x internal drive ratio = FDR FINAL DRIVE RATIO , then toy can go up or down in pinion gears as to keep motors and esc with in a good temperature ok hope i helped ok mugey

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