Yep. That was my one gripe with the ping sensors.

I believe it may be down to one or more of a few things;

1. Sonar sensors struggle to detect some materials. Sound absorbing materials are no good in this case.
2. Lost echoes and ghost echoes...
3. I read somewhere that the voltage supplying the sensor needs to be dead on for it to work correctly.
4. Poor quality wires - there are reports of some people using cheap Chinese cables to wire these and having problems, re-wiring with better quality solved the problem.

This is why I use IR and Ping. IR has it's pros and cons too but combine both and overall it's the best of both worlds.

I use (albeit pricey) devantech srf05 pings... they seem to be stable as I can't say I have seen the random 255 readings....

yes i have had same issue , my solution was to take 6 pings . drop the the 2 most of of range of the others. Use a mean of the remainder to plot object.

Hc sr04 ultrasonic sensors are notorious for easily being damaged if you accidentally connect a ping to a power and power to ping pin. Then they read a minimal amount or max 255 at that point. Based on public reputations maxbotics has the nicest ultrasonic sensors. A single sender and receiver and built in filter to reduce false readings from echos between triggered pings.

I do use the hcsr04 myself though because I can buy 5 sets and two are pretty good while the others are off.

There are intelligent ways to wait a few milliseconds between pings , pause then trigger and read echo. Once that first echo is read it waits a few milliseconds before triggering another ping.

Rich is absolutely right about the echo issue in a corner or on a edge. A SHARP I distance module uses angle of light transmission and receive angle to measure the distance. It's the most accurate but doesn't work against black very well or outdoors. Using a sharp module directly above the ultrasonic ping gives the best of both worlds. You can have script average the readings between the two I believe for better accuracy. That's something I have seen other hobbiest play with. Ezb combined with a pc has plenty of power to make the basic calculations.quickly.

That is why one should have PING and IR. And a Laser or Xtion would not hurt if you are serious about navigation.

Thanks for the tips guys!