Propeller System

[Daniel_LaFleur]

Originally Posted by AYang

Hi, my team (Apple Pi 2067) just finished competing at the Hartford, Connecticut Regional. Our ranking wasn't the best, but, individually, we did very well. We realized our potential as a defensive robot. We were brainstorming ways to add more pushing power. A fan in the back was one of the idea. I would like to hear suggestions or feedback from any team that has a propeller on their robot.

Thanks

You saw our propellers at BAE (Team 1729). We were able to pin just about anyone and were not pinned ourselves.

We used two 16" tri-blade Masterscrew 10 pitch propellers each directly driven by CIMs that gave us an additional 9 LBf thrust (basically doubling our thrust).

One bit of caution though, Since propellers use air movement to provide thrust, you need to consider the airflow path in front of (as well as behind) the propellers (seems like a 'no brainer', but ...). This means that you cannot 'just slap on' propellers and expect the results we got. The more disrupted the airflow (non-laminar) the worse the performance of the propeller.

The thrust of a propeller at static is almost all related to propeller diameter and RPM, having very little to do with propeller pitch until the robot starts to move. Additionally, the thrust of a propeller is non-linear to the RPM (and seems logorithmic). Thus doubling your prop speed will quadruple your thrust as well as quadruple the forces acting on the propeller.

Take care to watch the forces acting on the propellers, as they are not designed for the shock loads that a FIRST robot encounters. Because of this I suggest keeping well under the manufacturers recommended top RPM (We ran at 5500 RPM while our propellers were rated for 10300 RPM).

One last (and the most important) thing --- Safety. While most propellers are not very heavy, their high velocity means that they have a lot of energy in them. Please, Please, Please give yourself adaquate safety margin with your safety cage.

If you have any more questions, PM me. I'm more than happy to help out.