Replies to This Discussion

Permalink Reply by John on November 30, 2010 at 5:24pm

What do your ESC's and motors use?
Can they use the higher voltage without burning up?
Some ESC and some motors will allow higher voltages but some will not.
My motors and ESC's will only go up to 3 cells so I stop there.

• ▶ Reply

Permalink Reply by Arthur P. Meiners on December 1, 2010 at 1:16pm

Motor-ESC-Prop combo determines whether you can use 3S, 4S or even higher. RTF weight of the kopter and whether the motor is at or just past its optimum at full throttle on 3S determines whether the better choice is a higher mAh 3S battery or a similar mAh 4S battery. In both cases, you are increasing the Watt-hours available in the battery. If the motor is being pushed past it's max already at full throttle on 3S you won;t win much thrust but will dramatically increase heat production at higher throttle values on 4S and thus not be using the additional watt-hours for longer flight but increasing your in flight motor failure risk.

Everybody seems to think that higher volts is lower amps. However the motor is driven by the average volts provided as this is what drives the rpm. For a given motor-prop combo the same average voltage results in the same amp draw whether you have 3S or 4S or 5S. As you increase the voltage rpms and increase to a point where the motors is pushed passed its optimum at which point amps and heat production in the motor increase more rapidly and thrust and rpm hardly go up any more. With a smaller prop you decrease the resistance the motor has to overcome and thus reduce the amp draw and move the voltage and rpms at which overloading occurs up, but in the end this doesn't necessarilly result in a very different maximum thrust.

In the end the way to prolong flight times is to increase the reserve between actual RTF weight ex-battery and maximum RTF weight including battery. Two ways to do this: decrease weight of all other parts not absolutely necessary, and/or increase thrust without excessive increase in weight. The combination of the two is one reason why hexas and octos are interesting: they usually don't require a lot more frame weight than the quad, so the net-thrust (after correcting for the weight of the motor and motor mount) the motor is adding is more than for the first four motors. That additional net thrust can be used to add more watt-hours of battery power. This effect can usually be reached with the motors and ESCs you already have. The alternative if sticking with a quad is to find a lower kV motor which can swing a big prop at higher voltage (high static thrust) without overloading. If both the motors weight increase and the increase in frame weight to compensate for the higher forces is limited, you may also be increasing your battery payload capacity enough to allow for more watt-hours of battery weight to be carried which can translate in some level of increase in flight times.

• ▶ Reply