Explain everything about motors to someone new

[ColosTommy]

I've read some of the stickies here, and watched a number of different youtube videos in an attempt to understand motors and their workings. While this has worked to some degree, it has also left me with many more questions than i had at the start as well.

 

I was hoping some of the more experienced people here could help to impart some knowledge, and maybe if this thread goes well it could help other new people who get into the hobby and are somewhat overwhelmed by the huge choice and options that are out there.

 

From what i can gather there are a number of different factors that will affect how a motor will perform. For the sake of simplifying i will forget about sensorless vs sensored, and assume a set diameter to the motor. If there is something I'm missing off of this list, or more importantly I am understanding something incorrectly please reply, inform me and i will try to edit it.

 

1. The length of the motor: So a 4060 vs a 4070. Both have a 40mill diameter but one is 60mm long the other 70mm (A greater length=Higher KV but lower max RPM???)

Incorrect a larger length allows more magnets which can increase torque, but does not inherently mean a motor has more Kv

 

2.  The voltage you are using: So a 2400Kv motor ran on a different voltage will give different RPM (2s=17760rpm, 3s=26640rpm, 4s=35520rpm, 6s=53280rpm)

 

 

3. The Kv of the motor. With the same 6s a higher Kv motor increases RPM (2000Kv=44000rpm, 2400Kv=53280rpm, 2600Kv=57720rpm )

 

 

Everything seems to be geared toward increasing rpm (bad pun intended) when you upgrade your motor. There is no talk about increased torque or how an upgraded motor performs (better or worse?) in the low end torque acceleration.

 

Is the only reason to ever upgrade, if you are looking for more top speed, so need the increase of RPM (again forgetting the sensored vs sensorless side of things, and replacing due to mechanical failure)

 

Or is there a natural upgrade to torque and acceleration with the increase in rpm/Kv that is just never stated/quantified?

Or if you want the increase in torque acceleration but not top end, do you increase the motor Kv/rpm then gear the motor down with new pinions etc?

Torque is a product of Kv and Amps for a given motor, so a higher or lower Kv doesent mean more or less torque by itself.

 

Just trying to understand all the angles on this, it is alot to get your head around as a newbie.

 

Edited December 27, 2021 by ColosTommy

[locky]

 

[Nitroholic]

36 minutes ago, ColosTommy said:

 

1. The length of the motor: So a 4060 vs a 4070. Both have a 40mill diameter but one is 60mm long the other 70mm (A greater length=Higher KV but lower max RPM???)

 

Not exactly.

 

The diameter of the motor will give you an idea of hte power output, but the length of the can is nothing to do with the Kv rating.

 

If you think about it, what does a longer can actually mean?  In simple terms......longer magnets and more of the wire coils in the magnetic field. This gives more torque....and Kv is not a measure of that at all.

The Kv rating of a brushless motor is the ratio of the motor's unloaded rpm to the peak voltage on the wires connected to the coils. So basically....if you multiply the Kv rating by the voltage, you get a theoretical max rpm for the motor. Lower KV motors do tend to have more torque, but thats more to do with the current draw through the wiring than the length of the can.

 

You can have a short can motor with a low Kv.

 

I have upgraded motors to get more torque ..... and I have upgraded motors to get more 'poles' ..... as that gives a smoother power delivery with less cogging. It really depends on what you were missing in the original motor and certainly for me....it was rarely just to go faster

 

 

[ColosTommy]

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Deeper down the rabbit hole

 

Thanks so far, will go back and edit.

[ColosTommy]

It seems that you really have to dig into the specific motor manufactures specs on the motors to really get all the information you need, rarely do the websites that are selling the motors to the consumers seem to have all the detailed specs. Then you start getting into windings, and theres even more to figure out.

[Bajadre]

Brushed is a lot easier Colos the lower the turn the faster the motors the heavier the windings ie x2 will add more torque as for BL systems it is a mind field lol 😂

[ColosTommy]

It seems that you really have to dig into the specific motor manufactures specs on the motors to really get all the information you need, rarely do the websites that are selling the motors to the consumers seem to have all the detailed specs, and even it seems the manufactures themselves don;t help much.

Then you start getting into windings, and theres even more to figure out.

 

So you basically want the largest can you can (length) possible fit in your chassis, correct? As this should have more magnets? And will help with heat dissipation,  reduce thermal throttling and reduce the likelyhood of burning out the motor? Please tell me that statement is at least true

[Ross9999992]

Yes the bigger (diameter and/or length) it is the more powerful it is (generally) but usually amp draw is higher because of this.

 

Given the same size motors the lower the kv the higher the torque and so the larger the pinion usually can be. The lower the kv also the higher the voltage they can run up to a maximum of 40000rpm-60000rpm depending on manufacturer guidelines afaik

 

Heat is dealt with by gearing and driving style mostly though there are a couple of other factors (timing, punch, drag brake and brake force) that also effect it.

In short - Larger motor/lower kv/higher voltage = more torque.

 

Is there a specific vehicle you are looking at? Many options (motor/battery) can work for many models 😄 

[Nitroholic]

23 minutes ago, ColosTommy said:

So you basically want the largest can you can (length) possible fit in your chassis, correct? As this should have more magnets? And will help with heat dissipation,  reduce thermal throttling and reduce the likelyhood of burning out the motor? Please tell me that statement is at least true

No..... you want the RIGHT length can for the use. Not the biggest.

 

Let me tell you a cautionary tale....learnt the hard way.

 

I was converting a Hobao truggy to brushless, and I wanted to make it a beast....so I fitted the largest can I could get in there. A 4082 Leaopard motor. 150A ESc and planned to run it on a mix of 5S or 6S packs. Sweet, I thought. MAde some careful gear calculations, bought the right pinions...and took it for a spin. Ate the centre diff on first pack. Rebuilt the diff...shimmed it....tyres ballooned, and came off the rims. Re glued. Shredded the diff again. This time it got so hot internally, it melted the plastic diff case. Rebuilt with a locked centre diff filled with epoxy. Shredded front diff.

 

Just because it fits, doesn't mean its right. I ended up with a car that wheelied constantly, turned its tyres into pizza cutters, ate diffs, and could crash in a straight line. Fun....nope. After the ESC blew I sold it on as a roller.

 

 

[ColosTommy]

I own an Arrma Outcast 6s. I am not really looking to buy a new motor for it (hopefully), just started down a rabbit hole, realised i knew nothing (a common occurrence), and wanted to learn/understand a bit more about it all. There's plenty of threads of people saying fit this motor to that car, but i was more trying to understand the WHY and what advantages/disadvantages came along with each variable, and my god there are a lot of variables.

 

The only manufacturer i have found that really lists specs for their motors, and isn't just a glorified advert is TP Motors. Where you can choose windings and they give you a spec sheet to reference.

 

 

[Tug]

1 hour ago, Nitroholic said:

No..... you want the RIGHT length can for the use. Not the biggest.

 

Let me tell you a cautionary tale....learnt the hard way.

 

I was converting a Hobao truggy to brushless, and I wanted to make it a beast....so I fitted the largest can I could get in there. A 4082 Leaopard motor. 150A ESc and planned to run it on a mix of 5S or 6S packs. Sweet, I thought. MAde some careful gear calculations, bought the right pinions...and took it for a spin. Ate the centre diff on first pack. Rebuilt the diff...shimmed it....tyres ballooned, and came off the rims. Re glued. Shredded the diff again. This time it got so hot internally, it melted the plastic diff case. Rebuilt with a locked centre diff filled with epoxy. Shredded front diff.

 

Just because it fits, doesn't mean its right. I ended up with a car that wheelied constantly, turned its tyres into pizza cutters, ate diffs, and could crash in a straight line. Fun....nope. After the ESC blew I sold it on as a roller.

 

 

 

Sorry, but that's not a cautionary tale, it's a hilarious tale!

[Ross9999992]

Ahh fair enough. You can usually find info for specific motors with a bit of Googling I find but yeah there are many many options.

 

It’s not even just as simple as “use x motor for model z” because of the other factors. Speed runners I guess use far higher kv/taller gearing/higher voltages than bashers. Bashers generally just want reliability on all surfaces with reasonable speed etc. 

For 1/8 models most people run 4s-6s but if running 4s only then you can get away with hot <2800kv…running 6s <2200kv is about the limit. Regardless a 40mm+ diameter can seems to be the norm though it seems there are models out there running 4s with 36mm motors.

 

To a certain point voltage can decide max kv and then gearing to control speed/heat although lower kv can often be geared taller to achieve a similar speed as higher kv.

Run a pinion that’s too big and risk overheating your esc/motor….run a pinion that’s too small and risk burning your motor.

Running more volts than suggested for more torque but never hitting max rpm to keep temps down (throttle limit settings) can work but it’ll also pull more amps from your esc etc etc.

 

Tis a minefield. If/when a decision needs making then often the wisdom of the crowd is most helpful in these cases as long as you can decide on a few of the variables for yourself (model and voltage mostly) 🙂 

[babylon]

I have always had a much simple motor calculator, Buy anything in the 2000-2250 region, Job done.

When just bashing I believe there is sometimes just a little too much thinking going on. 

[ColosTommy]

This is less about the right motor for my purpose, as you say, just bashing around popping wheelies, in all honesty the stock motor is fine for my needs, and i dont 'plan' on upgrading excluding mechanical failure, was just more interested in the workings and details because its all like witchcraft to me.

[Nitroholic]

Its far from witchcraft ..... and the only things liable to get burned for it are ESCs!

 

It's like anything, really a question of how far down the rabbit hole you want to go. But as you have already found out, there is limited use in this for the hobby, as you simply will not find the necessary specs on a lot of motors. Same goes for ESC. Castle famously used to keep their max ampage on the ESCs a secret. Probably becuase it wasn't enough to make them sound good. If you find specs for a motor, they will tell you it's max amps....but knowing a max amp draw doesn't tell you what load they measured it under. Over gear a motor, and it will struggle to spin, pulling more current from the ESC as it tries. Pull enough current and the wires will melt from the heating effect....but your ESC will die before then. So really...the max amps your motor can draw would be a fairly big number....but not in normal usage. The Kv rating is based on no load rpm ....but you never run it that way. Its only useful to make comparisons and to predict likely performance and gearing needs.

 

Then, of course, these are 'manufacturers figures' which are liable to be inflated for sales reasons...

 

So, by all means jump in and do a load of research, but do it for the interest. Don't expect it to be all that useful in the hobby. You can use the knowledge to compare relative products, and to get an idea of what will be suitable for what model.....but there is still a big chunk of trial and error left for all of us. You get a feel for which makers give good data and which ones give a load of rubbish.

 

Lastly....I would suggest you broaden your research if you want to know more about brushless motors and how they work. They are used in a lot more applications.....but the principles remain. You will also find more solid articles about motors, magnetic fields and how the ESc works to drive the motor. Its a very different thing compared to a brushed motor....and probably help to make the motor stuff more understandable too.

[jariworsley]

If we are going down rabbit holes ...

Dare I bring up terms like "voltage sag" and ripple voltage? as well? 🙂

 

Its all interesting, but the more you pull on this thread the more is revealed. 

 

 

[ColosTommy]

 

 

Thanks Locky for posting that link.

 

I've now spent way too much time going through loads of his videos confusing the hell out of me 🙂

 

So according to this all things being equal, a longer can size will produce more torque and like wise all things being equal a larger diameter will produce more torque. Again as was said before it becomes somewhat useless when its very hard to get specs for motors in order to compare, but he has some interesting videos none the less.