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### Topic: Detecting Speed of Robot with Accelerometer. (Read 1 time)previous topic - next topic

#### Drew Davis

##### Jun 27, 2013, 07:55 pm
Hello, is it possible to use the sensor listed below to detect speed of robot? Normally I would just use motor encoders however they wont fit on the robot I'm using. If this sensors is not capable of it what sensor would work?

Thanks!

https://www.sparkfun.com/products/9652

#### johnwasser

#1
##### Jun 27, 2013, 08:09 pm
Accelerometers aren't very good at measuring speed because they only react to CHANGES in speed.  You have to add up all the changes to get the current velocity relative to the starting velocity and all that addition is subject to rounding errors that cause drift over time.

The best way to measure speed is with some kind of encoder.  You can paint stripes on the wheels and use a sensor to count the stripes as they go by.
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#### Drew Davis

#2
##### Jun 27, 2013, 08:58 pm
I don't really think any type of motor encoder is possible on my robot. Could I use and equation? For example say my robot traveled 12inches every 2 seconds at full speed. It's speed would be 6 inches a second right? Using a ruler and a stop watch I could determine how fast the robot moves depending on how much voltage I apply to the motor. Using math I'm guessing I could get pretty close to how fast the robot is actually moving. What do you guys think?

I'm entering in a competition and one of the task is to display how fast my robot is moving.

Thanks!

#### AWOL

#3
##### Jun 27, 2013, 09:24 pm
Quote
It's speed would be 6 inches a second right?

Wrong.
That would be its average speed.
If it moved from rest, then the maximum speed would be higher.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
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#### Drew Davis

#4
##### Jun 27, 2013, 11:45 pm
What if I had it move for a little bit of time before I started my calculations (time/distance)? If that will not work do you have any more ideas?

Thanks!

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