Underwater Sensor - range finder for collission avoidance

[Santosh]

Hi,

I would like to get information on what is the best approach on range finding underwater. I am very new to robots\ROVs. I would like to make a robot that operates on the bottom of the water and can find objects 3-5cm in front of it. I only need a boolean result i.e if there is an object within 3-5cm range return true else false. the robot will be used in a small tank or pool not larger than LXWXH = 3mx2mx1m. Since it's a very close area I need a very short range finder. Basically the robot is to stop and change path if object is found within the range specified. The object could be anything fairly small (say a 1cm diameter vertical PVC pipe to a large object eg wood log). The robot's speed will be very slow therefore the 3-5cm is enough to stop the ROV when the object is detected.

I have searched the Internet to gather information on which sensor to use, many ppl are pointing at ultrasonic sensor or IR.
But I am not sure which model/part can be used successfully underwater. Note: I do not need any video\pic of underwater, I only need the sensor to correctly identify the Objects blocking the path.

Kindly provide some information and guidance on this.

Thank you.

Regards,
Santosh

[Seawolf]

Ultrasonic is out. You'll be getting reflection off of the bottom, you might miss small objects, and the sensor's dead zone will be much larger than 5cm in front of you.

I'm not sure if IR will work either. Water attenuates IR frequencies pretty quickly. But, since you don't need very large range and the sensors are cheap, you might just try it and see what happens.

I personally would try some kind of a bumper sensor. Should be fairly cheap and simple to implement.

[Santosh]

Thanks for your reply seawolf.

Do you think a bend sensor will be effective? I see a bend sensor that bends 90* on 5gm of force is listed on $30+\pcs, too expensive. What is your thought about pressure sensor? is it possible to get pressure sensor that doesn't get triggered by the water pressure but works well when something touches it causing a very small pressure?

For bumper switch, should I place 2? One at the front left and one at the front right side or should I be looking at placing more (if bumper switch are the only sensors the robot will use).

For IR, I am not able to find cheap waterproof IR, do you think using IR covered by transparent waterproof stuff will work?

I have found the waterproof servo motor, water proof servo and I am planning to place arduino, shield and batteries on a waterproof box with servos wires coming out of it (will waterproof the hole from where the wires are coming out. Hopefully it will work.

Do you know any online store or website that sells very sensitive bumper switch or other switches suitable for this project?

Thank you.

Regards,
Santosh

[fryslan76]

Hi Santosh,

I would think that a bumper sensor will be triggered by the forward motion of the ROV when they are to sensitive. For pressure sensors the difference between the surrounding pressure and something touching the ROV could be small. So you would need frequent messaurements to compare the difference between two moments.

Regards.

[fryslan76]

Hi Santosh,

I would think that a bumper sensor will be triggered by the forward motion of the ROV when they are to sensitive. For pressure sensors the difference between the surrounding pressure and something touching the ROV could be small. So you would need frequent messaurements to compare the difference between two moments.

Regards.

[Seawolf]

Do you think a bend sensor will be effective? I see a bend sensor that bends 90* on 5gm of force is listed on $30+\pcs, too expensive. What is your thought about pressure sensor? is it possible to get pressure sensor that doesn't get triggered by the water pressure but works well when something touches it causing a very small pressure?

For bumper switch, should I place 2? One at the front left and one at the front right side or should I be looking at placing more (if bumper switch are the only sensors the robot will use).

For IR, I am not able to find cheap waterproof IR, do you think using IR covered by transparent waterproof stuff will work?

I have found the waterproof servo motor, water proof servo and I am planning to place arduino, shield and batteries on a waterproof box with servos wires coming out of it (will waterproof the hole from where the wires are coming out. Hopefully it will work.

Do you know any online store or website that sells very sensitive bumper switch or other switches suitable for this project?

Bumpers are going to require some trial and error. You don't want it to be so sensitive that the water you're moving through triggers it, yet you want it to be sensitive enough that it will detect objects. I haven't actually used bumpers (or bend sensors) underwater, so I can't help you there.

As for the IR stuff, you can try buying a cheap one and putting it in some transparent casing. Make sure you do some research on the casing though. Just because something is transparent to visible light doesn't mean it will be transparent to IR. Test it outside of water to make sure that the casing works before you put too much trouble into waterproofing it.

[berossm]

I know this topic is a little old but I've been looking at accelerometers for other parts of my control system. Several of them have interrupt lines for impact detection so if you are already using a micro-controller this might be a easy way to go.