brushless questions to prove a point
 

I am having an arguement with a friend of mine and want to prove my point. So as to not suggest what I think and just get your answers, I am onlt allowed to ask the question and get your answers.

1. What KV is a faster motor. a 3500kv or an 8000kv motor?
2. When an esc is rated for 6S, does this mean two 3 cell batteries, or does it mean two 6 cell batteries?
3. Can you run 2 brushless motors on the same spur gear and gain twice the speed, or is there a slight gain with 2 brushless motors?
4. Are there faster and better RC Brushless electronics than Novak, and LRP?
5. Can Lipo batteries explode with out proper balancing?

Thanks, Hopefully your answers will be the same as mine to prove a point.

Ohh and are any of them ESC motor combo's on ebay for the heli's fine to run in an RC18T. This one I dont know and would like to get some opinions on if so and which one? Laters.

The higher KV number, the more RPM per volt, doesnt mean the motor is faster, just spins more RPM per volt, higher KV motors are less efficient, which means heat

6s is 6 lipo cells, so thats 22.2 volts, doesnt matter how many of what cell you use, its a 22.2 volt limit......

2 BL motors is dumb really, the gain is more torque, so yoou can use the toque to gear up, but really its not much a gain..........

theres much faster stuff the LRP/Novak...... NEU, LMT, Pletty, Mega, KB, ETC And then low end motors like BK, feiago (sp?)

Lipos will only blow up if they are damaged like punctured or, shorted out..... Balancing doesnt mean the cells wont blow up, just keeps the cells voltages the same which makes the pack last longer, and have better performance....

1. 8000kv will spin faster for given input voltage but may be slower due to having to gear down for lack of torque.

2. 6S means 6 series connected Lipo Cells at a nominal voltage of 3.7V/cell

3. Most people only get a marginal amount of increase in speed, nowhere near double.

4. Definitely

5. Typically, no. Also, most don't explode when they have a problem, they catch on fire. Balancing will help keep the cells from dropping too low in voltage relative to the other cells in the pack though. So, if you have perhaps a 6V cutoff, they both stay at 3V each, versus one staying much higher and one much lower. If one perhaps does drop too (<3V), there is a potential for the Lipo pack to puff up, but typically nothing more than that.

1. The 8000kv is faster, assuming the same voltage is applied to both motors.
2. A 6cell rated esc is rated for 6 cells wired in series. So you could wire 2 3cell packs in series and get 6s, or you could wire 2 6 cell packs in parallel and have 6 cells worth of voltage and double the capacity (mah)
3. 2 motors should produce twice the speed, by allowing you to gear up, but you will run into other issues like diretrain drag and wind resistance that usually increase exponentially as speed increases, so NO.
4. Most sensorless systems produce more power than lrp and novak. You can use higher voltage on them than 2s lipo, so they will produce more power (simple explanation, a better one will most likely be given by someone who knows more than I)
5. Lipo batteries do not explode, however if they are improperly charged or discharged they undergo a chemical reaction that produces gasses that will make the pack expend (puff). I have puffed a few and yet to see any explode. They may pop due to the pressure, but no bomb-like explosion will happen. Sometimes they catch on fire, but I have not seen that happen either.

A link to the heli setup would be handy, although they will most likely not have reverse or proportional brakes, so you may want to stick to a car esc, like the mamba 25.

see my input in blue...

My 2c on the first question. The 8000 will be faster as it will be more powerful as it will have a lower resistance and use more power and in a perfect world produce more power in theory. In practice with other factors the lower kv motors can be faster. The higher KV motors often can't produce the torque to reach their theoretical max rpm due to heat and current requirements.

Not exactly. Most motors from a given manufacturer, of the same series, but different kv ratings produce equal torque if all else is equal also. The difference comes because of the limits of the motors. For example; Mamba Max motors all have the same max rpm, lets say 60,000. To get a motor to that rpm, a certain amount of voltage would have to be applied. To find out how much voltage you need, take the rpm and divide it by the motor's rating. To get the lower kv rated motor to the same 60,000 rpm, it would take a higher voltage. With current being equal in both systems, the higher voltage system makes more watts of power, since watts are voltage * current. They both will be spinning 60,000 rpm (making neither motor faster), but the higher voltage system will have more horsepower. The higher horsepower system can pull a bigger gear, and thus go faster.

Voltage * Current = Watts
745.6 Watts = 1 HP

Actually, it's all about the torque IMO. The formula is:

torque (in ft-lbs) = 1352 / kv X amps / 192

As you can see, increasing amperage and/or reducing kv increases torque. So, for a given amperage, the lower kv motor will have more torque.

FYI: you can also calculate HP without voltage and current:

Mechanical HP = torque X rpm / 5252

Would not torque and horsepower be equivalent in a rotating system? As torque is the turning force to overcome a load in a rotating system, so is horsepower a pulling force to overcome a load in a linear one. Since someone many years ago started using the value of horsepower to describe the force in a rotating system where torque should have been the standard, I don't think that in this instance they can be separated. I can gurantee that a vehicle with no rated horsepower, also generates no torque as well.

Torque and HP are proportional. HP is defined as torque over a period of time. The unit of torque in the SI system is (kg*m^2)/(s^2), and HP is (kg*m^2)/(s^3). Torque ((kg*m^2)/(s^2) * RPM (1/60s) gives you the unit of HP. So that 5252 BrianG gave must just be a proportionality constant.

Isn't horsepower a unit of power and torque is just force. We can convert HP into watts but not torque to watts. Heck I can put a bolt on at 150 FT/lbs but can't move it at that rate more than 1/8 rpm so my horse power is very low. It is is two different types of measurement, thats why you need both.

I've always thought about torque vs HP like this: Torque is how much you can lift and HP is how fast you can lift it (or something like that).

What you say about the bolt tightening analogy makes sense. If you have a certain amount of torque at a certain rpm, you can "gear up" to multiply the speed, but torque is reduced by the same amount. HP should be the same no matter what "gearing" you use though since the same work is being done, just at different speeds.

And yeah, the 5252 thing is a constant, but can't remember what. I do know it does work though...

I always considered horsepower a measurement of the potential to do work, not a measure of the amount of work being done.

http://en.wikipedia.org/wiki/Torque

go to the "conversion to other units" section and read about the 5252

Torque = force x distance (it's ft-lbs, not ft/lbs, lbs is a unit of force)
Torque can be converted to watts if there is a specified time over which that torque operates.