I have some questions regarding building a gearbox for a motor to create a robot actuator. Given my desired motor and loads, I've determined that a gear ratio in the 400-700 range is adequate for my application.
Here is my motor choice for reference: http://www.robotshop.com/ca/en/banebots-rs-550-motor-12v-19300rpm.html
Here are my questions:
1) Mounting gears to a motor: if I have a motor with a shaft diameter of 0.12in (3.2mm), what size gear bore should I use, and how do I attach a gear to the shaft in practice? I'm not that mechanically inclined (yet).
2) Say I build a gearbox of ratio 625:1, as such: https://www.youtube.com/watch?v=lF-4qVBWy88 I have no idea of how "durable" such a set up would be. For my application, I am looking at moving an 8kg mass from 0.6 meters away, coming out to a total torque of 47 newton meters. How can I tell if the gears will break or not?
For reference, these are the gears I'm looking at (and I'm pretty sure they're the same ones in the video): http://www.vexrobotics.com/276-2169.html
3) Assuming those gears above were to fail, what type of gear material would be recommended for my load application of max 47nm?
4) What efficiencies can one expect from gears of different types? I've been assuming 50% conservatively as another answer mentioned.
Thank you for any help, and please let me know if anything was unclear.