Science Buddies: "Ask an Expert"

Hi, I am helping out with a STEM project at a local school.
we are building an autonomous little robot.
I am helping with the software and one of the students asked this question that I could not answer.

Speed of Servo
If I understand this correctly all servos have speed ratings.
The speed varies based on supplied power. (at 6 volts a servo is faster than at 4.8 volts)
If a servo operating at 6 volts is said to have an operating speed of 0.20 sec/60 degrees no load
will it take 0.005 sec to move 15 degrees?

Can you help me answer this question?

Thanks

tomega3 - You are obviously referring to a DC servo, probably with a gearbox. Simply, the specifications you state, .20 sec/60 degrees at no load would move 15 degrees in one-fourth the time, or in .05 seconds. Small math error in your calculation. The no-load speed of this servo is 1.2 seconds per revolution, or 50 RPM.

Rick Marz

Thanks Rick,

so its roughly 50 milliseconds to move 15 degrees with the dc servo rated at 6v 0.20/60 degrees

The reason this question came up is to figure out when to sample an ultrasonic sensor after sending a move servo command

We will do some testing, the goal is to move the servo in 5 degree increments which should take roughly 16.67 milliseconds
So to be safe we can start reading the sensor 20 milliseconds after issuing a servo move 5 degrees command

Tom

The expert or whatever didn't take into account that the motor has to speed up to the maxium speed and then slow down. The servo speed is the fastest it will move. When you test you'll find out that it takes a lot longer per degree for a small motion then for a bigger one. I've been making robots for a long time and I actually know about servos.

Maybe you know about RFID & stuff? Can you help me with my question? viewtopic.php?f=30&t=15734

Hi robotz,

Thanks for the advice, we will test different wait times to see what works.

With regards to your rfid project here is a link that may help you get started:
https://opensource.com/education/15/3/a ... -rfid-tags

Tom