I’ve been spending time in the esk8 force calculator, and some interesting things made themself more obvious as I played with parameters.
First, let’s take a look at basically a pretty standard high voltage board (HV) with 130kv motors. I have already bumped up the motor amps to 95a. This is a very powerful board, but how can we push it to extreme levels of power.
You might think, let’s slap a lil foccer in there and push the amps to 150a per motor, but take a look at our motor torque. We are already at 7Nm, which means we are at the max torque of many common motors (reacher 6485 for example). Increasing amps at this point will just saturate the magnetic field and turn the motors into space heaters, regardless of what the theoretical calculator spits out for force.
Next, let’s look at a basically equivalent setup with higher kv motors. If you increase the gear reduction to compensate for higher kv motors, you end up with the same top speed and power.
Going higher kv, we have less motor torque for the same amount of amps, but we have increased the gear reduction, so we end up with the same amount of torque (then force) at the wheel.
One interesting thing to think about here is, just changing motor kv, our motor is operating in a lower torque range on every ride we will ever go on. The motor in v2 below, will never have access to operate in the 4.4-7Nm torque range. This will have an effect on efficiency.
Most of our outrunners are very efficient at >0.7Nm torque. If we end up substantially increasing the amount of time our motor spends operating below 0.7Nm, I suspect we will negatively impact motor efficiency. Borrowing some real world data from @Tony_Stark , shared in the radium motors thread.
What if we are building a race board and what maximum power? Let’s increase amps to push those motors to the torque limit. This gives you an unreasonable amount of force at the wheels. Like, truly an amount 95% of us would never come close to touching. But, if you are building a hill climbing race board / BDE flex monster, this is the path.
In summary, if you want the highest performance available, high voltage, high kv, high amps is what you should pursue. Not ground breaking, but I think it is interesting to understand why this is the case.
If you are running high voltage and reasonable amps, kv probably doesn’t matter as much as you think it does, so long as you adjust with gear reduction. Depending on how you ride, you could see better efficiency on 130kv or 205kv.
I posit that you will get better efficiency, if you can gear reduce and choose a motor kv that gets you riding more often in the 0.7nM-2Nm “high efficiency range”.
