Motor Turns and the torque they provide (Full Version)

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Ripcaster -> Motor Turns and the torque they provide (5/13/2008 2:03:09 PM)

Ok, I'm still a bit new but I know a thing or two about electricity and electronics.

My question is: Are low turn motors better for backyard bashing (grass, hills, some pavement, packed dirt, etc) than high turn motors?

Now here's why I ask:

The evader ext comes with a 20T motor. For all the reading I've done I thought the rule was "The higher the turns, the more low end torque you get, and the lower the turns, the more RPM you get resulting in a faster car".
Thus, low turn motors are better for racing on tracks with long straights where high top end is desirable. High turn motors are good for twisty tracks where getting out of the corners quickly (i.e. acceleration) is desirable.

I deduced that backyard bashing would warrant a high-turn motor so that the low end torque combined with torqy gearing would get through grass, over hills and bumps and so on. More turns = stronger electromagnet and thusly more pull to the permanent magnets in the can. Fewer turns give less attraction to the magnets, but makes the armature turn faster.

I just read an article on misbehavin that seemed to say the opposite, and it seems logical to me as well: more turns = more weight adding a type of flywheel effect to the armature. Inertia would make it harder to start from a stopped position, and easier to keep running when at full speed. Lower turns weigh less and thus are easier to start and get up to speed (which indicates more low end torque, the opposite of what I thought).

I purchased a 27-turn Trinity motor (TRI12000) last week and it's blazing fast now, I love it but with 17:88 gears the motor still gets quite hot after a mix of pavement and grass and hard packed dirt (we have it all in my neighbourhood). Should I have gone with a lower turn motor?

I see the Traxxas products (I'm looking heavily at a Pede incidentally) come with 12t motors (granted they're bigger, 550's).



Longhair -> RE: Motor Turns and the torque they provide (5/13/2008 2:08:10 PM)

You have to have the proper gearing so your motor does not get excessively hot no matter what motor is used.



SavageX78 -> RE: Motor Turns and the torque they provide (5/13/2008 2:19:58 PM)

The 12 turn 550 from traxxas burns out pretty quick.
And well it is very torquey its not that fast.

You may need to drop a tooth or 2 for the 27 turn.
I have a trinity p2k2 in my mf2 now and it is pretty quick and the brushes are doing very well.And im geared 19/86.
I also drive on dirt grass and hills and the motor does get too hot to touch but its still under 150F when measured with a temp gun.
I can run 2-3 packs through it without cooldown time and it still stays around 150f

I highly recomend getting a temp gun if you dont have 1 already. there about 20 bucks and its the best purchase ive made. It helps alot when trying to hit the sweet spot with gearing. And it helps with making sure you dont burn out your motor or blow your batts.



Ripcaster -> RE: Motor Turns and the torque they provide (5/13/2008 5:18:26 PM)

Stock gearing was 20:88, so I'm already dropped to 17:88. You think I should go lower? Probably have to get a bigger spur to do it, running out of motor adjustment room with the smaller pinion. :)

That said, maybe my motor is still below 150F. It's too hot to touch longer than 2 seconds sometimes, sometimes 4 seconds. Batts don't warm up much though. Sounds like even though the motor's hot it might still be operating correctly and good gear ratio?

But back to the question, do high turn or low turn motors provide more bottom torque. I still think it's high turn motors; look at the rock crawlers with 65T and so on. I'm inclined to believe that Misbehavin is slightly off in stating that the extra wire weight of high turn motors means that the power is provided at the top end. I subscribe to the theory that more wire means more magnetism and thus it's easier to start a motor that's highly loaded (going up hills, rough grass etc).




Access -> RE: Motor Turns and the torque they provide (5/13/2008 5:40:31 PM)

Not all motors are equal. The cheap motors that come in stock vehicles are in a class all their own. They can often be outperformed by a stock 27-turn motor.

Starting torque, the more turns, the better. It is a linear relationship, 60 turns will have twice the starting force than 30 at a given amount of current. But there is a saturation point where no more torque can be generated regardless of current. This saturation point is based on the cores of the electromagnetic coils, typically around 2 tesla I believe.

Once it starts to spin, there are more factors than just turns. You have things like the power / quality of the permanent magnets and such.

What the turns really controls is how quickly the torque falls off as RPM rises. A 60 turn motor might have half torque at 4000rpm and little torque at 7000rpm. A 30 turn might have half at 8000rpm and very little at 14000rpm. A 19 turn might have half at 15000rpm and little at 28000rpm.

Now brushed motors can be very picky with gearing, don't overgear or undergear them. Overgearing is the worst as it tends to cause excess heat, but undergearing (or just running the motor with the wheels lifted off the ground) can cause arc'ing or over-rpm'ing which can also be bad for a brushed.

For gearing, b'cos a 13-turn has a higher max RPM than a 19-turn, it will have to be geared lower. But the 13-turn doesn't necessarily have less torque; at any given RPM (other than very low RPMs like pushing into a wall or getting started) and especially the higher ones, it will have more torque than the 19-turn. Not less.

For brushed motors use the '5-second rule', if you cannot hold your finger on the motor for 5 seconds at any point during or after the run, it is geared wrong, typically overgeared.

Cheap stock motors or other silvercan motors are often mass-produced or built using cheap meteriels. Remember the armature, comm, and brushes make a mechanical switch so whether they use copper, aluminum, or steel/iron there makes a big difference how much current you can pass through without it getting too hot.

"I subscribe to the theory that more wire means more magnetism and thus it's easier to start a motor that's highly loaded (going up hills, rough grass etc)."
Theory? It is a proven fact...
It is not necessarily the amount of wire, but the number of turns of wire around the core.
But more turns also means higher inductance / impedience, hence the falloff of torque as the RPMs increase.



thedr -> RE: Motor Turns and the torque they provide (5/13/2008 5:43:32 PM)


quote:

ORIGINAL: Ripcaster
Ok, I'm still a bit new but I know a thing or two about electricity and electronics.
My question is: Are low turn motors better for backyard bashing (grass, hills, some pavement, packed dirt, etc) than high turn motors?
Now here's why I ask: The evader ext comes with a 20T motor. For all the reading I've done I thought the rule was "The higher the turns, the more low end torque you get, and the lower the turns, the more RPM you get resulting in a faster car". Thus, low turn motors are better for racing on tracks with long straights where high top end is desirable. High turn motors are good for twisty tracks where getting out of the corners quickly (i.e. acceleration) is desirable.


I think you're confusing power with speed with torque, and they're not the same thing. And if you're comparing closed-endbell stock motors from different companies you're also going to have a hard time making side-by-side specification comparisons. The deal is with most motors is that power and run-time is more relative to wind count, the lower the wind count the faster its going to be and the higher the wind count the more runtime you can expect, while the torque and RPM themselves is more relative to whether its single double or triple strand wind so thus a 13T x 1 (or single) is going to have more torque than a 13T x 3 (or triple) though the triple wind is going to be smoother powerwise and is going to turn more RPMs. It's been my experience the biggest thing is that you want to pick a motor relative to what you're doing and where you're running, and thus if you have a big open area in which you're running you can use the ponies developed by a lower turn motor, while if you're in an enclosed area (like your smallish backyard track) you have little need for something real powerfull and are likely more interested in getting the most runtime to increase your funtime.
The magnets really have nothing to do with it as far as you're concerned since magnet quality/power is only relative to the quality of the motor. Better/more expensive motors = better magnets, cheaper motors = cheaper/less powerful magnets. It has nothing to do with how many thruns the motor is other than lower tun motors are generally of better quality and thus they get better magnets.
As far as any perceived weight difference between lowturn and highturn motors, while what you pointed out was correct, it really has little in the way of relative benefit to what you're trying to do as you're only talking nano/milli-seconds worth of difference. This is something way overthought or overconceptualized.
When you purchased the Trinity stock motor the reason it appears faster is that it's of better quality than most kit motors that are notorious for being of low quality. But, because stock motors draw relatively low voltage and amperage, they tend to run a long time and that's why you noticed increased heat. Electric motors get hotter the longer they run and the more power they draw.

hope this helps



Ripcaster -> RE: Motor Turns and the torque they provide (5/13/2008 6:15:13 PM)

All very valuable information. It certainly helps to know more about this stuff, but I got a bit confused in your response:

A 13 X 1 motor will have more torque than 13 X 3? Why would one electromagnet pull toward the permanent mangets more than 3 electromagnets working together? I'd think it were the other way around.

Also, my automotive mind takes over here a bit and thinks about torque vs. horsepower. Torque residing in the lower RPM range, making the motor difficult to bog down, and horsepower residing in the top rpm range, providing the power required for high speed/high gearing applications. Power is defined as the total area under the torque and horsepower curves whether they're weighted toward torque, HP, or both. :)

THUS: backyard bashing in grass and such would require a lot of torque (on a global scale) since the car can get bogged down. Sure torque to the wheels can be changed by gearing, smaller tires etc, but purely in the motor's context I'd like something that provides a lot of torque as opposed to a lot of top end. Now a very "powerful" motor would probably provide both top speed and low end torque (certainly more than a factory motor :P), and that's what I'm interested to find out. Do motors with a lot of low end torque have a high number of winds, or a low number?



Access -> RE: Motor Turns and the torque they provide (5/13/2008 7:24:20 PM)

quote:

ORIGINAL: Ripcaster
A 13 X 1 motor will have more torque than 13 X 3? Why would one electromagnet pull toward the permanent mangets more than 3 electromagnets working together? I'd think it were the other way around.

Also, my automotive mind takes over here a bit and thinks about torque vs. horsepower. Torque residing in the lower RPM range, making the motor difficult to bog down, and horsepower residing in the top rpm range, providing the power required for high speed/high gearing applications. Power is defined as the total area under the torque and horsepower curves whether they're weighted toward torque, HP, or both. :)

You can't compare the two. Forget everything you know or assume about an internal combustion recipricating engine when dealing with electric motors.
You have basically unlimited torque at the very low RPMs, and torque starts to fall off in a semi-hyperbolic fashion as the RPMs increase. At very low RPMs, the only limit on torque is the mechanical construction of the motor.

What he discusses above are winds (not turns). This is basically akin to limiting the thickness (and hence the current maximum) of the wire used. If you learn the proper technique for driving an electric from the ground up, this is not really necessary. If on the other hand you are trying to drive an electric like you drive a gas or a nitro vehicle, too much torque on a low-traction surface is a bad thing, lowering the torque can make it easier to drive consistently or just stay on the track. Just don't 'gun' it, walk that throttle up gradually and be patient getting up to speed.

If you imagine your torque curve as a hyperbole that slowly falls off as RPM increases, now cut off the top of that hyperbole, flattening it, based on the maximum current allowed to flow (could be limited by batteries, ESC, or motor winds).



thedr -> RE: Motor Turns and the torque they provide (5/14/2008 2:45:55 AM)


quote:

ORIGINAL: Ripcaster
A 13 X 1 motor will have more torque than 13 X 3? Why would one electromagnet pull toward the permanent mangets more than 3 electromagnets working together? I'd think it were the other way around.


I think you think something is happening with motors that isn't. Electric motors generally speaking all have two polar opposite magnets, not a varying number. So a 13x1 motor is a single wind motor (13 wraps of a single strand of wire), while a 13x3 is a triple wind (13 wraps of a small gauge triple strand of wire) and that's why the single wind has more torque. Basically the single strand by being more direct allows the current to grunt its was through, while the triple strand is a little more efficient and doesn't overpower the armature as easily. Does that make sense?
So in this case motors with torque can come in all sorts of numbers of winds. It all depends on what sort of runtime you're looking for. More winds 27T vs. 13T = more runtime for the 27, while the 13T will be faster and give you shorter runtimes.
As Access said, don't let your automotive mind take over conceptualizing this in your mind. You're talking electric motors here and not internal combustion engines.
Otherwise, all the stuff Access said. [8D]



xism -> RE: Motor Turns and the torque they provide (5/14/2008 3:47:52 AM)

interesting... i always believed a motor was stronger if it had more winds



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