Quote:
Originally Posted by tjump
An additional direction with this query: how would running lower voltages equate to robot performance (torque) if we used lower V+ (brushless motor speed is related to input voltage and running at 6 volts would cut top end rpm to 30,000 or less depending on Kv of the motors).
Anyway, we are just trying to dig deep into motor/gearbox/battery power design to understand the relationship in all of these (several posts on other robot building sites spend a great deal of time discussing higher voltages equaling better robot motor performance... i.e. 24V systems vs. 12V systems). We want to understand how to put all of this together.
I appreciate the input.
Cheers,
Timothy Jump
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I'm not sure about the quality of the FP gearboxes, but I can answer some questions about brushless motors.
However for your torque question, that is easy. Power output of any motor is going to be: rpm X torque X a constant (changes based on units). So, half the voltage is half the rpms. When you give half the voltage, the max amperage becomes half also (Ohm's law). So, half torque. In turn, doubling voltage gives twice the power.
This can be a bonus in overall performance (velocity, kinetic energy, ect.) of the system if you can use batteries with similar capacity at 12 and 24volts because you get 4 times the power at twice the weight. However, your batteries will need to put out twice the amps and will then run out twice as fast.
When selecting a motor you will need to have some idea of what you need it to do. Power output is the real important one. You can gear it however you like, BUT more gearing will cost you more in weight. This is sometimes important.
If you are looking for applications under 8k rpms, you may consider a brushless outrunner instead of an inrunner like you mention above. They provide fewer rpms per volt, but more torque, giving similar power outputs as inrunners. And they will need less gearing.
If I may make a suggestion on motors, the Great Planes rimfire series are good quality but won't break the bank like Axi brushless motors can. Found here:
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GHG
I have heard good things about Turnigy series motors too. Not sure where they are bought though. I haven't shopped for a brushless motor in a while, but the above principles still apply (physics doesn't change).
Best of luck,
Jeff