# measure distance

• posted

Im building an electronic south pointing chariot for my uni project and i need to measure the distance travelled by the wheels and input the distance from the sensor to a microcontroller... any ideas on how to do that?

below is the detail of my project... any ideas welcome

The chariot is a two-wheeled vehicle upon which is a pointing figure that always point in the same direction (of the compass) as the chariot moves. South Pointing Chariot - Wikipedia, the free encyclopedia

Requirements: The figure on top of the chariot should always point to the same direction of the compass regardless of the chariot's motion.

The pointing direction is read from the PC.

As the chariot moves, the distance that the wheel(s) travel should be collected.

The trajectory (direction and distance) that the chariot follows is recorded in the PC.

Hardware must be on stripboard or PCB.

I know how to build this mechanically, but not electronically. I need ideas on how to implement this electronically.

• posted

n

You do realize that the "pointing" requirement isn't explicitly linked to the "trajectory" requirement? So it would be perfectly legal and spec-compliant for you to control the pointing figure using a regular magnetic or gyro compass, and record the trajectory using an accelerometer.

Reading between the lines of the project description, your instructor appears to want you to perform odometry on each wheel. Google "quadrature encoder". You will measure the total number of [fractional] revolutions of each wheel, and calculate the trajectory based on your knowledge of the wheel diameter and - presumably - some empirically-determined allowance for slippage.

However, you can play considerable games with specmanship here. Using an accelerometer to measure the actual trajectory, and knowing the radii of your wheels, it is easy to work the same calculation backwards, and it can give you a much more accurate trajectory plot.

So, as with any busywork - dance around the spec to optimize your performance on the features your customer is actually measuring.

• posted

A small nit concerning your terms.

A bullet follows a trajectory.

The intended direction of your device is its course. The direction it is pointing is its heading.

The direction and distance it has traveled is its track or course made good.

• posted

First off, I presume you know that you're not really measuring, or need to measure, distance. If you look at the mechanism in the original gadget, you know that it's basically a car differential, geared to the figure with the proper ratio. You could use encoders on each wheel, take the difference, and use these to drive a stepping motor.

Or, you could cheat. Depending on your professor's temperament, this could get you an A+ or an F. For the ultimate cheat, see

Or, if your professor likes complexity, you could do as larwe suggests, and integrate the output of a gyro. Parallax has a gyro (in fact, full IMU) package as well. _AND_ a GPS receiver. Or, you could do a combination of all of the above. It could be as much fun as you have time and money to make it.

Good luck!

Jack

• posted

ce

n

Wheel sensors will suffer from some slip effects.

Optical Mouse components are cheap these days, and may fit inside your speed/distance needs ?

-jg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.