Motor sizes explained

[biggman100]

I know this is probably on here at least a dozen times, but, either im not finding it, or im just not understanding what im reading, so, here goes. If you pick a static KV, lets says for this example 3500KV, what are the differences between a 3650 and a 3660 moor? Would they be the same? Would one have more speed or more torque over the other? Some of you have already seen my other post about ESC's and motor's, and the reason i didnt just add to that thread is because in trying to understand what motor did what, leaving the ESC out of it, i got confused even worse.

 

[Gherik]

I am interested in this also. The way motors are sized in this hobby confuse the heck out of me.

 

[DoNoHarm]

Greater motor size means more torque period. If you have a 3650 can with 3500kv, a 3660 can with 3500kv will spin exactly as fast, but because it has more torque, it'll run cooler, allowing you to gear it up and have a faster vehicle overall. This goes for a diameter increase or length increase. Realize, diameter increases are much more noticeable. For example, if you take a 3674 longblock 10th scale motor and compare it to a 4074 8th scale sized motor, that 4074 will have close to double the power, despite being only 4mm wider, and the same length. Now if we take a 4082 motor and compare it to a 4074, it'll have a minor torque increase, despite being 8mm longer.

The first 2 numbers is the diameter of the motor. The second 2 are the length. Let's do an example. A hobbystar 4276 motor (my go-to company and motor) is 42mm wide (diameter) and 76mm long.

Traditionally, as you go up in motor size, you go down in kv. While you may be able to purchase a standard 3650 10TH scale motor with 3500kv, you'll realize that most 4074 8th scale motors will max out around 2200kv. However, you can run it on much greater voltage and gear it up to go MUCH MUCH faster than that 3500kv 10TH scale motor, while barely breaking a sweat. The bigger the motor the more amps it draws, so that's why 90% of the time you need a new esc as well.
Here's my rule of thumb:
For longcan 10TH scale motors, (3670 and 3674) your best bet is a castle mamba max pro, castle mamba x, or hobbywing max10 SCT. For 8th scale motors (4074) the cheapest I'd go is the hobbywing 8BL150, but personally I love castle so i go mamba monster 2, but many love the mamba monster x. I just have trouble getting with times and my MM2 has been ultra reliable (and I even run motors that pull way too many amps) but the esc just takes it.
For 6th scale motors go hobbywing max6, for 5h scale motors use a castle XLX or a hobbywing max5.

 

[biggman100]

Greater motor size means more torque period. If you have a 3650 can with 3500kv, a 3660 can with 3500kv will spin exactly as fast, but because it has more torque, it'll run cooler, allowing you to gear it up and have a faster vehicle overall. This goes for a diameter increase or length increase. Realize, diameter increases are much more noticeable. For example, if you take a 3674 longblock 10th scale motor and compare it to a 4074 8th scale sized motor, that 4074 will have close to double the power, despite being only 4mm wider, and the same length. Now if we take a 4082 motor and compare it to a 4074, it'll have a minor torque increase, despite being 8mm longer.

So, if i am reading this correctly, a 3660 would provide more torque, so, to get more speed, you would run a lower gear? This is where i get the most confused, is the whole gearing for torque vs gearing for speed. Reading this, if i read it right, it would seem that a 3650 would give more speed, whereas a 3660 would give more low end grunt, unless im really missing something somewhere.

 

[DoNoHarm]

So, if i am reading this correctly, a 3660 would provide more torque, so, to get more speed, you would run a lower gear? This is where i get the most confused, is the whole gearing for torque vs gearing for speed. Reading this, if i read it right, it would seem that a 3650 would give more speed, whereas a 3660 would give more low end grunt, unless im really missing something somewhere.

Yup you’re completely missing it. Reread this message.

Greater motor size means more torque period. If you have a 3650 can with 3500kv, a 3660 can with 3500kv will spin exactly as fast, but because it has more torque, it'll run cooler, allowing you to gear it up and have a faster vehicle overall. This goes for a diameter increase or length increase.

KV is KV. Size doesn’t change it. Size changes torque. Speed doesn’t change unless kv changes.

 

[biggman100]

Ok, so, overall, a 3660 is better, as long as it is geared right (by better i mean will run cooler, which in turn causes less heat overall, which translates to less destruction of equipment). That little bit made more sense to me than the last few months of reading combined did. Thank you for that. My next question is, is a 60A ESC too small for say a 3660 in the 3100 to 3900KV range for the following trucks: my Warhawk, which right now has a Racers Edge Pro2 3600KV of unknown size in it, an Associated SC10 4WD, and a Losi TEN-SCTE 4WD?

 

[Cheapbastard]

KV is (loosely) RPM per volt. Apply the same voltage they will both spin the same amount of RPM's per volt. The difference is rotor size.

Different rotor size as the numbers change in the size of the motor the rotor is either longer, shorter, wider, or skinnier. A 3650 motor will have a shorter rotor than a 3660 motor.

Put a crank (on the shaft) and belt (the width of the rotor) on each one and apply a load the larger rotor will have more power as the load increases but take a greater amount of power to sustain the load (more surface area to turn). The smaller rotor will be easier to turn until the load increases (smaller belt).

Take a 3074 and 4074 motor. The 3074 will have the same length but smaller diameter rotor. Each rotation of the larger diameter rotor will require more power to turn but with each rotation have more torque (small cog big cog).

Since a lower Kv motor spins at a slower speed the difference (in RPM's) is made up in voltage then you go into gear ratios and is a different story.

 

[joostin420]

Greater motor size means more torque period. If you have a 3650 can with 3500kv, a 3660 can with 3500kv will spin exactly as fast, but because it has more torque, it'll run cooler, allowing you to gear it up and have a faster vehicle overall. This goes for a diameter increase or length increase. Realize, diameter increases are much more noticeable. For example, if you take a 3674 longblock 10th scale motor and compare it to a 4074 8th scale sized motor, that 4074 will have close to double the power, despite being only 4mm wider, and the same length. Now if we take a 4082 motor and compare it to a 4074, it'll have a minor torque increase, despite being 8mm longer.

The first 2 numbers is the diameter of the motor. The second 2 are the length. Let's do an example. A hobbystar 4276 motor (my go-to company and motor) is 42mm wide (diameter) and 76mm long.

Traditionally, as you go up in motor size, you go down in kv. While you may be able to purchase a standard 3650 10TH scale motor with 3500kv, you'll realize that most 4074 8th scale motors will max out around 2200kv. However, you can run it on much greater voltage and gear it up to go MUCH MUCH faster than that 3500kv 10TH scale motor, while barely breaking a sweat. The bigger the motor the more amps it draws, so that's why 90% of the time you need a new esc as well.
Here's my rule of thumb:
For longcan 10TH scale motors, (3670 and 3674) your best bet is a castle mamba max pro, castle mamba x, or hobbywing max10 SCT. For 8th scale motors (4074) the cheapest I'd go is the hobbywing 8BL150, but personally I love castle so i go mamba monster 2, but many love the mamba monster x. I just have trouble getting with times and my MM2 has been ultra reliable (and I even run motors that pull way too many amps) but the esc just takes it.
For 6th scale motors go hobbywing max6, for 5h scale motors use a castle XLX or a hobbywing max5.

I also thought the same about motor length until I purchased my tp 4070cm 2200kv motor; which is 40mm diameter but 107mm long

 

[2fast4u]

So, if i am reading this correctly, a 3660 would provide more torque, so, to get more speed, you would run a lower gear? This is where i get the most confused, is the whole gearing for torque vs gearing for speed. Reading this, if i read it right, it would seem that a 3650 would give more speed, whereas a 3660 would give more low end grunt, unless im really missing something somewhere.

I think you understand that a physically larger motor of equal Kv to a smaller one will produce more torque. This in turn can allow a higher gear ratio to attain more speed at the same rpm. The confusion I think may be with gear ratio's in itself. A higher ratio (lower numerically) will net more speed for a given rpm, but puts more load on a motor. A lower gear ratio (higher numerically) will produce less speed for a given rpm, but puts less load on a motor. That ratio is attained by dividing the number of teeth (or diameter of a pulley) on the driven gear/pulley by the number of teeth (or diameter of a pulley) on the drive gear/pulley. So for example if you have a 12 tooth pinion and a 50 tooth spur the ratio is 4.16 to 1. If you have a 16 tooth pinion and a 50 tooth spur the ratio is 3.12 to 1. The former is slower (lower) but more torque multiplication, the latter is faster (higher) but less torque multiplication.
If you allready understood this,,, Sorry.
It's difficult to ascertain who may allready know what.

 

[DoNoHarm]

Ok, so, overall, a 3660 is better, as long as it is geared right (by better i mean will run cooler, which in turn causes less heat overall, which translates to less destruction of equipment). That little bit made more sense to me than the last few months of reading combined did. Thank you for that. My next question is, is a 60A ESC too small for say a 3660 in the 3100 to 3900KV range for the following trucks: my Warhawk, which right now has a Racers Edge Pro2 3600KV of unknown size in it, an Associated SC10 4WD, and a Losi TEN-SCTE 4WD?

Exactly!

 

[DoNoHarm]

I also thought the same about motor length until I purchased my tp 4070cm 2200kv motor; which is 40mm diameter but 107mm long

Then you got scammed or hooked up (depending on how you look at it) or the seller mislabeled it.

 

[joostin420]

No, I think you misinterpreted ? It is the correct size to the specifications but the tp 4070cm 2200kv is not 70mm as you would think going by the logic of the 10’s signifying the motor length; instead it is 107mm. So why doesn’t it follow the logic is my question

http://www.tppowerusa.com/tp-4070-cm-2200kv

It’s so long ?

 

[DoNoHarm]

That is by far the weirdest thing ive heard. Learn something new every day. Anyway yeah, those tp’s are sooo long. I’d mount one in my revo if the shocks didn’t get in the way.

 

[jamesbcn]

Joostin, on your TP motor, did you order 5mm or 8mm shaft?

 

[joostin420]

5mm shaft

 

[Jerry-rigged]

On the motor sizing think, realize different manufacturers measure motors differently. Most Chinese motors are an can diameter times can length. Other Motors are size stator diameter X rotor length. Castle and Tekin both use this second measure system. However, note that castle motor dimensions are in tenths of an inch not millimeters. So that a castle 1406 is actually the same size as a Chinese 3650.

 

[Evol_13]

The first 2 numbers is the diameter of the motor. The second 2 are the length. Let's do an example. A hobbystar 4276 motor (my go-to company and motor) is 42mm wide (diameter) and 76mm long.

Thant you for this!!! And honestly your whole explanation just cleared this whole thing up for me!

I have been trying to understand how these motors are being rated. And while I understand the Kv and even Ohms Law, I was missing how the sizes where being measured.

 

[olds97_lss]

However, note that castle motor dimensions are in tenths of an inch not millimeters. So that a castle 1406 is actually the same size as a Chinese 3650.

Can you explain that a bit more? How do you get 36mm or 50mm out of 1406?

 

[Jerry-rigged]

For the 1406 -
The diameter is 14 = 1.4" = 35.5mm
The rotor length (not can length) is 06 =0.6" per castle specs, this motor can is 49.5mm long. So this is a 540 size motor.

For a 1410, same 1.4"=35.5mm can diameter, but the rotor is now 1.0", and the can is 53mm, so a 550 size motor.

For the 1415, same diameter, but the rotor is 1.5", can length is 70mm. So 3670 size

Interesting, though, the 1515 is listed as 75mm long, even though it has the same 1.5" rotor length. 1515 = 4075 size.

 

[DoNoHarm]

Can you explain that a bit more? How do you get 36mm or 50mm out of 1406?

To be honest I just know that a castle 14 series is 36mm wide and 15 series is 42mm wide, and 17 series is 45mm wide