I am in the process of designing a jumping robot, im trying to keep the weight below 2 kg, The robot works by compressing two helical springs with a linear actuator. The maximum force reaches 350N. I need a method to drive the rack and pinion and I am currently considering a reduction gear train. But I need to find the most light weight solution. Is bldc motor with a reduction gear train a good idea? With a 1400kv bldc motor my calculations show a gear ratio of 65 000, this will have to include about 5 set of 3d printed gears. Are bldc motors even suitable for high torque low rpm applications, is there any other motor I can use? There are also 12V gear motors available. I have allocated about 300g for the whole motor + gear train assembly.
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Assuming frequency of jumps is not an issue...
Since the springs are responsible for the jumping, not the motor, you want the highest torque in the lightest package possible so you can compress the largest spring possible with the least weight. So this is the lightest motor you can get with the highest gear reduction.
BLDC motors are fine for high-torque low RPM applications, particularly with sensored drives. But brushless is pointless here since brushless motors have advantage in efficiency and power output, but since the springs are doing the jumping none of that matters here unless you need to wind up the spring faster so you can jump more frequently.
As a hobbiest, it's easier to find brushed motors with really high gearboxes off the shelf than it is to find brushless motors with gearboxes of any kind. A brushless motor drive is also much more complicated than a brushed drive. If your mechanics only requires you to turn the motor in one direction then all you need is a single transistor for a brushed motor. A brushless motor driver can inherently drive a motor backwards and is more than six times as complicated (requires 6 transistors plus sensors and controls).
Wear safety glasses. Maybe even a face shield. A 350N spring releasing is no joke.
