A Bumper Update

By | 06/12/2020

Officially on holiday for two weeks!

Next up on the robot, after getting the wheel encoders working, are the bumper triggers.  These are essentially the same as the wheel encoders so I can reuse the circuit I put  together and they’ll be on interrupt pins too.  Thankfully the Arduino Mega I upgraded too has another two spare.

The reason for using triggers is that these act as an estop of sorts, as soon as you hit something the robot needs to Do A Thing.  There’s a video I saw an age ago of one of the engineers tearing down a Roomba and explaining how and why they built it in certain ways and he said they used the left and right triggers together to figure out where the bumper was hit.  If only the left or right trigger it’s one of those two sides but if they both trigger you can use the difference between them to figure out roughly where on the bumper was hit.

The benefit here is that if you know where you struck something you’ll be able to react more accurately.  For example, if only the right trigger is activated then you can make an educated guess that you only need to move a little left after backing up but if it’s somewhere in the middle you’d need to move a lot sharper to either side.

Something else I’m doing is replacing the battery pack with three Lithium Ion cells from the scavenged laptop batteries.  I have a couple of 3-cell caddies for them which will give ~12v which will be enough for this robot.  I dug out the connection from the existing battery to the power switch and it was held in place with hot glue!  I’m no longer hacking, I’m continuing a proud iRobot tradition. 😛

I’m hoping to have a video in the coming week as with the wheel encoders and bumpers I’ll be able to get basic movement working, there’s a distance sensor on the right hand side which should just need an analogue read on the Arduino too.  There are a lot more sensors on board, each wheel has a “lifted” sensor and there are a bunch of downward-facing sensors on the bumper too, but I’ll deal with these in time.  The downward facing ones are cliff sensors so that it doesn’t fall down stairs, for now it’ll be supervised anyhow so not too much of an issue.

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