Granite 4600Kv motor w/3s = mangled spur

[bicketybam]

Personally, I would stick with 2S. Maybe use a 2S HV pack which get you a little more speed.

Best regards,
Brian

For a 4600kv motor, yeah 2s only. If you really want 3s, run a lower kv motor.

I had to try and besides the roasting hot temps, it was a total blast!

I was looking at this esc/motor combo from Castle: http://www.castlecreations.com/en/m...5-2v-wp-esc-and-1415-2400kv-combo-010-0160-00

What I fear is that I'd have to run 4S and it still wouldn't perform like the 4600Kv motor on 3s. From what I've read, Kv is RPM per volt. A 4600Kv motor on 3s is 51,060 RPM. A 2400Kv motor on 4s is 35,520 which is a hair more than running the 4600Kv motor on 2S. I'm sure the Mamba-X will run more efficiently and cooler, but I don't need to spend $220 for that. Am I making any sense? I am new to all of this and the whole Kv/volt relationship is confusing the heck out of me.

 

[Bri26]

The 3400KV version of this combo would be ideal for 3S - https://www.rcjuice.com/hobbystar-1...hless-4-pole-motor-includes-program-card.html

The ideal motor size for the Mega 4x4 is a 540 4 pole motor, 3900KV or 4300KV for 2S and 3400KV for 3S.

Best regards,
Brian

 

[bicketybam]

The 3400KV version of this combo would be ideal for 3S - https://www.rcjuice.com/hobbystar-1...hless-4-pole-motor-includes-program-card.html

The ideal motor size for the Mega 4x4 is a 540 4 pole motor, 3900KV or 4300KV for 2S and 3400KV for 3S.

Best regards,
Brian

So if I am understanding this correctly, 37740 RPM is about the max (3400Kv on 3s).

 

[Bri26]

That's basically correct if going by nominal voltage. A full charged 3S pack will put out 12.6 volts, so in this case, you get 42,840 RPM.

Best regards,
Brian

 

[Jerry-rigged]

I had to try and besides the roasting hot temps, it was a total blast!

I was looking at this esc/motor combo from Castle: http://www.castlecreations.com/en/m...5-2v-wp-esc-and-1415-2400kv-combo-010-0160-00

What I fear is that I'd have to run 4S and it still wouldn't perform like the 4600Kv motor on 3s. From what I've read, Kv is RPM per volt. A 4600Kv motor on 3s is 51,060 RPM. A 2400Kv motor on 4s is 35,520 which is a hair more than running the 4600Kv motor on 2S. I'm sure the Mamba-X will run more efficiently and cooler, but I don't need to spend $220 for that. Am I making any sense? I am new to all of this and the whole Kv/volt relationship is confusing the heck out of me.

Your current motor is a 1408, right? and that one you are looking at is a 1415. So the rotor is almost twice as long (0.8" vs 1.5" long, if I understand Castle's naming system). So at the same RPM, same current draw, that 1415 will be making about 2x the power of your current motor. But it needs about 2x the voltage to get to that RPM. The good news is that the power needed to drive your truck at 40mph is the same regardless of which motor you are using. So the real world result is the 1415 2400kv on 4s is drawing half the amps to make the same power. At half the amps, temps will be greatly reduced - maybe not half, but a lot less. Plus bigger motor = more surface area to dissipate heat, so again, lower temps. And again, lower amps at the ESC and battery = cooler running, longer life for them too.

If you did want to run that 1415 2400kv motor to the same speeds you are currently getting with the 4600kv on on 3s, you can still get the same speeds - but you will need to gear up. My motor is 2000kv and I am currently running 15t/56t gearing - 1:3.73. Stock gearing is 14t/91 - 1:6.5. So I (about) doubled the gearing to make up for the low KV motor, and I run on 4s to keep the RPM's up. Results = Bat outta hella and smashed driveline (4074 torque (in Castle speak, this motor is closer to their 1717 fatter (more power) and longer (more power)))

Math sux, but it also works.

 

[bicketybam]

Your current motor is a 1408, right? and that one you are looking at is a 1415. So the rotor is almost twice as long (0.8" vs 1.5" long, if I understand Castle's naming system). So at the same RPM, same current draw, that 1415 will be making about 2x the power of your current motor. But it needs about 2x the voltage to get to that RPM. The good news is that the power needed to drive your truck at 40mph is the same regardless of which motor you are using. So the real world result is the 1415 2400kv on 4s is drawing half the amps to make the same power. At half the amps, temps will be greatly reduced - maybe not half, but a lot less. Plus bigger motor = more surface area to dissipate heat, so again, lower temps. And again, lower amps at the ESC and battery = cooler running, longer life for them too.

If you did want to run that 1415 2400kv motor to the same speeds you are currently getting with the 4600kv on on 3s, you can still get the same speeds - but you will need to gear up. My motor is 2000kv and I am currently running 15t/56t gearing - 1:3.73. Stock gearing is 14t/91 - 1:6.5. So I (about) doubled the gearing to make up for the low KV motor, and I run on 4s to keep the RPM's up. Results = Bat outta hella and smashed driveline (4074 torque (in Castle speak, this motor is closer to their 1717 fatter (more power) and longer (more power)))

Math sux, but it also works.

My current motor is a 1406. I don't understand the relationship of rotor size to RPM.

 

[Jerry-rigged]

There really is no relationship to rotor size and RPM, that I know of, other than larger motors tend to be lower KV. But they can be wound for higher KV, it just is not normally done. BUT bigger rotors = more torque, so bigger motors can make more total power. At least, that is my layman's understanding.

 

[GuyFromCanada]

BUT bigger rotors = more torque, so bigger motors can make more total power.

The magnetic fields generated by a given length of rotor (rotating part) and stator (attached to motor case) will add for each unit length. So a rotor/stator pair that is twice the original length will generate magnetic fields that are "twice as long" generating twice as much attraction for twice as much "torque". Torque is dependent on RPM though, so you need to factor that in. In 1:1 scale cars, they will supply the torque for a given RPM, say 6000 which is often near the "red line" on your tachometer and the reason is simple: higher RPMs mean higher torque:

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

Now when it comes to the kV rating, a single loop of wire will generate 1 "unit" of magnetic attractive force. If you wrap the wire around twice, you will get more attractive force...I'm sure it isn't twice, but it is some positive scaling factor. The reason for this is that the attractive force from the first loop will add to the attractive force of the second loop, and so on for additional loops (I don't want to use "turns" because that is already used by people to rate real motors, and I don't want to add confusion since I'm not sure what a turn means exactly...) The strength of the magnetic field is proportional to the current through the wires, and the current through the wires is equal to roughly voltage across the loop divided by the total resistance of the loop (I say roughly because I'm not differentiating between DC circuit theory and AC circuit theory...AC circuit theory factors in the effects of capacitance and inductance...the inductance is significant since it is proportional to the number of loops). Increase the voltage, and you increase the current, which increases the magnitude of the magnetic field, which increases the attractive force, which increases the rate at which the rotor rotates...hand wavingly of course.

What @Jerry-rigged said about the current is also very important...for a given amount of power transfer, since Power=Voltage*Current, you can achieve the same power with a higher voltage and lower current. The power dissipated (and therefore heat dissipated) in the windings of the motor, or the switching circuitry of the ESC is Current*Current*Resistance...so reducing the current while increasing the voltage can have a significant impact on the efficiency of the overall power system.

...or something like that.

 

[bicketybam]

There really is no relationship to rotor size and RPM, that I know of, other than larger motors tend to be lower KV. But they can be wound for higher KV, it just is not normally done. BUT bigger rotors = more torque, so bigger motors can make more total power. At least, that is my layman's understanding.

Gotcha. I think my choice is down to either the Castle 1410 3800 Kv motor running 2s or the Castle 1415 2400 Kv motor running 4s. With my new understanding of Castle's numbering system (first two digits refers to the diameter of the stator and the second two digits refer to the stator length), I am leaning heavily towards the 1410-3800 running 2s. I am fearful that the 1415 will be too much torque for the drivetrain.

 

[GuyFromCanada]

The 1410 3800kV is what I'm running, with the Mamba X and I really like it. With softer start and braking, I think 3S could be done for speed, with 2S for general bashing. If you can control yourself with starts and stops, then 3S is probably pretty reasonable, but I'm heavy on the throttle and brake and don't trust myself. The problem with the 3800kV motor is finding stock...you could buy the Mamba X for the programmable BEC, then pick up a cheap China sensorless motor, and that would get you going pretty quickly...

 

[bicketybam]

The 1410 3800kV is what I'm running, with the Mamba X and I really like it. With softer start and braking, I think 3S could be done for speed, with 2S for general bashing. If you can control yourself with starts and stops, then 3S is probably pretty reasonable, but I'm heavy on the throttle and brake and don't trust myself. The problem with the 3800kV motor is finding stock...you could buy the Mamba X for the programmable BEC, then pick up a cheap China sensorless motor, and that would get you going pretty quickly...

Yep - the combo is back ordered everywhere, including Castle's site. I signed up for alerts from Tower and Amain. I'll just run my current setup until they come in. Thanks everyone for all the help!

 

[GuyFromCanada]

Yep - the combo is back ordered everywhere, including Castle's site. I signed up for alerts from Tower and Amain. I'll just run my current setup until they come in. Thanks everyone for all the help!

You might want to place backorders at a bunch of places. There were supposed to be parts coming in June 22nd and July 5th, but I never got alerts. I presume stock was used up by backorders, and then some. Once you get a shipping confirmation, just cancel your other backorders.

 

[bicketybam]

You might want to place backorders at a bunch of places. There were supposed to be parts coming in June 22nd and July 5th, but I never got alerts. I presume stock was used up by backorders, and then some. Once you get a shipping confirmation, just cancel your other backorders.

I ordered from Amain. Hopefully the wait isn't too long.

 

[Jerry-rigged]

Gotcha. I think my choice is down to either the Castle 1410 3800 Kv motor running 2s or the Castle 1415 2400 Kv motor running 4s. With my new understanding of Castle's numbering system (first two digits refers to the diameter of the stator and the second two digits refer to the stator length), I am leaning heavily towards the 1410-3800 running 2s. I am fearful that the 1415 will be too much torque for the drivetrain.

Yeah, me too. I have had that 1410, 3800kv Mamba X combo on backorder from Amain for a while now. The last chat I had with them was on the 5th, and they said that Castle was showing stock arriving at their warehouse, on the 5th. Amain said it takes about a week for that stock to get to them (amain) then probably another week to me. So I am hoping to get mine somewhere around the 19th...

 

[bicketybam]

Yeah, me too. I have had that 1410, 3800kv Mamba X combo on backorder from Amain for a while now. The last chat I had with them was on the 5th, and they said that Castle was showing stock arriving at their warehouse, on the 5th. Amain said it takes about a week for that stock to get to them (amain) then probably another week to me. So I am hoping to get mine somewhere around the 19th...

Is that going in your Granite?

 

[Jerry-rigged]

The magnetic fields generated by a given length of rotor (rotating part) and stator (attached to motor case) will add for each unit length. So a rotor/stator pair that is twice the original length will generate magnetic fields that are "twice as long" generating twice as much attraction for twice as much "torque". Torque is dependent on RPM though, so you need to factor that in. In 1:1 scale cars, they will supply the torque for a given RPM, say 6000 which is often near the "red line" on your tachometer and the reason is simple: higher RPMs mean higher torque:

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

Now when it comes to the kV rating, a single loop of wire will generate 1 "unit" of magnetic attractive force. If you wrap the wire around twice, you will get more attractive force...I'm sure it isn't twice, but it is some positive scaling factor. The reason for this is that the attractive force from the first loop will add to the attractive force of the second loop, and so on for additional loops (I don't want to use "turns" because that is already used by people to rate real motors, and I don't want to add confusion since I'm not sure what a turn means exactly...) The strength of the magnetic field is proportional to the current through the wires, and the current through the wires is equal to roughly voltage across the loop divided by the total resistance of the loop (I say roughly because I'm not differentiating between DC circuit theory and AC circuit theory...AC circuit theory factors in the effects of capacitance and inductance...the inductance is significant since it is proportional to the number of loops). Increase the voltage, and you increase the current, which increases the magnitude of the magnetic field, which increases the attractive force, which increases the rate at which the rotor rotates...hand wavingly of course.

What @Jerry-rigged said about the current is also very important...for a given amount of power transfer, since Power=Voltage*Current, you can achieve the same power with a higher voltage and lower current. The power dissipated (and therefore heat dissipated) in the windings of the motor, or the switching circuitry of the ESC is Current*Current*Resistance...so reducing the current while increasing the voltage can have a significant impact on the efficiency of the overall power system.

...or something like that.

Specing motors can get confusing...

Talking about turns gets a bit crazy. Per textbook physics, yes, increasing the turns on a motor pole increases the magnet field, which increases motor power, but in real world physics, it also increases wire length, which increases voltage drop, which reduces power... Think of a 50t crawler motor vs a 26t "Stock" brushed motor vs a 12t motor. Exactly backwards from what textbook physics says. The "Real true physics" involvs a dozen or three different variables that no-one talks about, wire diameter, wire length, power source, brush type, magnet type, etc...

KV is not much better, as "all things being equal" higher KV should give higher power - but all things are never equal, and we almost never use our motors at max power anyways - not for more than about half a second, anyways.

Even trying to read max wattage can get misleading, as otherwise identical motors may have radically different max wattage, just due to one being a 2s max motor and another being a 4s max motor.

So, (IMHO) in the end it comes down to finding some general rules that mostly work most of the time, and trying to fit them with the way you run your hobby. For my car I don't really race, so I want a big can, lower KV, that I can run at a higher voltage so everything stays cool.

 

[Jerry-rigged]

Is that going in your Granite?

I bought that combo 'for' my Hobao SCT, but I will for sure run it in the Granite 4x4 too, just to see how the truck runs on that size motor.

 

[GuyFromCanada]

So, (IMHO) in the end it comes down to finding some general rules that mostly work most of the time, and trying to fit them with the way you run your hobby.

That was an "all else being equal" examination. I hadn't really thought about things until I wrote that down so it was as much for me as it was for anyone else. If anything, some "textbook" knowledge can help you ask questions on why two otherwise similar rated motors or ESCs might be rated differently...there is a lot of stuff that doesn't make it into marketing materials, and possibly it could be for a good reason.

In the end, I couldn't agree more...being new to driving, I'm still learning some general rules of what not to do so I don't screw up my truck again. I'm happy if I can make it through a single lipo with the truck still working.

 

[bicketybam]

Man, I just lucked out! I went to a LHS I have never been to before and asked about the Mamba X 1410-3800 combo. He didn't have it bit he had the Mamba X in a crawler combo and the 1410-3800 in an SCT combo. He split the two and sold me the combo for the same price as the Mamba X/1410-3800 comno! I'm so pumped!!!

 

[GuyFromCanada]

Man, I just lucked out! I went to a LHS I have never been to before and asked about the Mamba X 1410-3800 combo. He didn't have it bit he had the Mamba X in a crawler combo and the 1410-3800 in an SCT combo. He split the two and sold me the combo for the same price as the Mamba X/1410-3800 comno! I'm so pumped!!!

Nice! Just to double check, what is the motor shaft diameter on the motor you scored?