Sensor to detect boulder in robot?

[dardeshna]

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

[dirtbikerxz]

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

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

[GeeTwo]

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 (https://www.pololu.com/category/79/sharp-distance-sensors), or plenty of other locations.

[jSchnitz]

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 (https://www.pololu.com/category/79/sharp-distance-sensors).

[euhlmann]

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

[Hitchhiker 42]

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.

[hardcopi]

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.

[frcguy]

We used this (http://www.jameco.com/z/SEN0019-DFRobot-Switch-Infrared-Sensor-3-80cm-Detection-Adjustment-0-5V-100mA_2144462.html) 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 (https://www.google.com/maps/place/Jameco+Electronics/@37.5227642,-122.2645311,15z/data=!4m2!3m1!1s0x0:0xbef28fac5eede1af?sa=X&ved=0ahUKEwjr1Ojpt_vOAhUT3GMKHerVBysQ_BIIcTAN) to pick it up.

[adciv]

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.