Distance measuring/tracking

Hey to all! Im a newbe with an ambitious project!

I need to use arduino to track objects moving on a straight line. The line is 100m long. The objects speed will vary.. At the 50m mark 9m off to the side is where my robot will stand. The robot consist of an electric whealchair base. So far the motors are hooked up to a sabertooth motor controller and its can be controlled via rc remote.

As the objects move on that straight line the robot has to keep facing towards them. Just a paning motion.

The straight line is a narrow dirt track. The objects are horse riders armed with bow and arrows. The robot will hold a 3feet diameter target.

I will attempt to use a pixycam based irlock but its might be too far for that to pick up the ir beacon relably.. And the price of the beacons are 150.. That is just the board with the led's. Each rider would need one so thats a lot of money.

Im thinking that probably would be better if i could measure the distance of the riders as they move on the track and use that data to turn the target.

Any good ideas? I literally just learned today how to make an led blink.

I was thinking might be a small radio with the rider could give out a ping and at the end points two arduino could pick it up and caculate the location? Talking to the robot?

Petimoritz: Any good ideas? I literally just learned today how to make an led blink.

Making an LED blink is one thing, but doesn't allow people to estimate your experience in systems integration etc. You mentioned - "newbie". Newbie at arduino? Or newbie and both arduino, tracking objects, systems integration etc?

I was thinking might be a small radio with the rider could give out a ping and at the end points two arduino could pick it up and caculate the location?

Nope.

Outdoors, GPS is about all there is. Indoors on smaller scale, use an overhead video camera with motion tracking software on a PC.

Use a laser range finder, a distance of 100 meters is no problem. Don't know if they're cheaper than your 150 in unspecified currency, but you can get them for less than 150 in USD. (note: don't know if this model can work with Arduinos, just the first Google result).