Friction is resistance caused by two surfaces moving past one another.
Here’s an example. Say you put a piece of rubber on a smooth plastic surface at an angle. The rubber won’t slide off unless you tilt the surface really far up, because the friction between the rubber and the plastic is high, especially compared to that of another smooth plastic on the plastic ramp. Friction is what makes the rubber harder to slide along the surface. What’s also neat is that you can determine the coefficient of friction, which is used in friction calculations, from this experiment. You simply find the angle that the surface is tilted at when the object starts to slide, and that’s the coefficient of friction of the surface.
When it comes to gears, friction is bad because it wastes energy that could be going towards moving your system. Imagine rubbing your hands together on a cold day to warm them up. That works because of friction, producing energy.
In this example, that energy comes from you moving your hands together. On a robot, that energy comes from the motors.
Now, obviously you want to get all the power you can from your motors to your wheels, with as little as possible getting lost in the drivetrain, which is why excess friction is bad. It can make your robot slower and weaker than it should be, and if one side has more friction than another, it can cause your robot to not drive straight.
Friction in gears trains generally comes from two places: the gear teeth sliding past one another (which we can’t really do a whole lot about in vex) and the shafts moving on the bearings.
So yes, too many gears means more teeth sliding past one another, which means more friction. If possible, keep it under 7 as a general rule of thumb.
But yes, Friction can be mitigated in longer gear trains with good build quality. This includes:
- Screwjoints, an alternative to using a bearing in an axle to transmit motion. This generally uses a free-spinning insert on the gear, which is lower friction because it is a round hole spinning around a round surface, as opposed to a square hole turning in a round surface.
A good description of how to create screwjoints can be found here:
Harvard-Westlake Robotics: AMOGO x DOGO Reveal - #31 by Unionjackjz - Make sure everything is aligned. When things are misaligned, it puts the shaft at an angle in the bearing, creating more pressure on it and more friction.
- Also, a few legal greases and lubricants are included in the game manual, which can be used on gears and shafts to keep friction to a minimum.