Sensor to detect boulder in robot?
 

We've looked at a few ultrasonics to detect once a boulder has entered our mecanum roller intake, but most don't really start working until 8in range or so. Any other ideas to sense a boulder with in 3-4in? We can probably get ultrasonics to work but I feel like there might be some "proper" way to do this. IR doesn't seem to work at close proximity. Thanks!

EDIT: Looked at this ultrasonic - http://www.maxbotix.com/Ultrasonic_Sensors/MB1220.htm

Re: Sensor to detect boulder in robot?
 

We used ultrasonic. I can find out exactly what sensor tomorrow.

Re: Sensor to detect boulder in robot?
 

We used IR. For short ranges, there are better IR sensors available at low cost than ultrasonic. You can find some with ranges as short as 2 cm 0.5 cm and a price point of $10 or less at Pololu, or plenty of other locations.

Re: Sensor to detect boulder in robot?
 

Sharp has great IR sensors in ranges as short as 2cm. We used a 2-15cm and a 4-30cm model this year and loved them. They also have a .5cm model. Link.

Re: Sensor to detect boulder in robot?
 

We also used a Sharp short range IR sensor. It's worked very well.

Re: Sensor to detect boulder in robot?
 

I feel like a garage door IR sensor could be useful here, if you could hook it up. Something like that could be made very accurate.

Re: Sensor to detect boulder in robot?
 

We used a simple IR sensor. Worked perfectly. It triggered the ball to stop and the pickup wheel stopped it within an inch or so.

Re: Sensor to detect boulder in robot?
 

We used this IR sensor we got from Jameco. I see you are in the Bay Area, so if you need it relatively soon you can order online and go to Jameco's store in Belmont to pick it up.

Re: Sensor to detect boulder in robot?
 

You have multiple options. Depending on specific configuration, you have:
1) IR Sharp Distance Sensor (provided analog voltage whose inverse correlates with distance.
2) IR Proximity Switch (Goes true when object detected within X inches)
3) Break beam sensor (see garage door sensors)

Be warned with the IR Prox Switch, some do not pick up specific colors/materials reliably. We had one last year that could not reliably detect Gray Totes. If it is truly inside your robot, a break beam would be the most reliable.