Servos

VEX V5 General Discussion Technical Discussion
1

I know what servos do, and what they are supposed to be used for (claw arms etc.). However, in actually building a robot I haven’t found a practical use where a servo would work better than a regular 393 motor. We have a lot of servos laying around and I was wondering if I could find a use for them. My question is this: Have any of you guys used a servo on a VRC competition robot,
and where and why? Motors seem to do everything I need done on my VRC robot, so why are servos a thing?

2

Years ago, I used a servo to shift a 2-speed transmission.

3

Well a more fair comparison would be a servo to an old 3 wire motor. Which has identical torque and speed.

You would choose a servo if you only ever wanted 180 degrees of rotation and wanted good control on it. Anything to activate a mechanism, pull pin etc would be an easy example

4

Servos are great for accurate positioning with automatic hold. The Vex servos don’t have a lot of torque, but they work well for precise gripper mechanisms. None of our games have needed that directly, but it doesn’t mean they won’t. Shifting transmissions is a good use of a servo, and they’re particularly useful when you have to shift precisely to more than the two positions @Rick TYler mentioned. We’ve used a servo to slide the driven wheel across a friction drive plate. (Here’s a famous example: https://www.tripadvisor.com/LocationPhotoDirectLink-g34618-d246824-i120969465-Sarasota_Classic_Car_Museum-Sarasota_Florida.html) In our robotics application, the parts were much smaller. The servo lets you hit the same position accurately, so you get accurate “gear” ratios.

5

Depending on the direction of the forces involved, a gripper may not need a lot of strength in the direction the motor/servo applies it. Maybe the direction is perpendicular to that. Imagine, for example, having a spatula you want to swing sideways under something, while the vertical is supported by structure (and a lift other than the swinging bit). Now you get to choose if you use a heavier motor in addition to sensors to make sure it rotates to the right position or using a single, lighter servo and not using up sensor space.