Autonomous Recharge?

I’ve been interested in the feature of the IRobot Roomba that can plug itself in and recharge itself when it’s batteries are low. (Roomba 560) I’ve been thinking of how to replicate something like this. My idea was to have the plug in on the charging base sticking out in a static position, with the other plug (hole) on the robot. On either side of the base pin would have a laser pointer, and on either side of the hole would be a photoresistor. So, you could program it to back in to the charger, and when it gets close the base turns the laser’s on. Then, the robot would rotate back and forth until both resistors are lined up with the lasers, then it would back in straight, adjusting itself as is does.

Is this plausible?

Sure it is but i’d do a more user friendly plug. Similar to what a cordless phone uses with pins and contact pads. Also simple guide rails on the base to simplify things.

Better yet why not have it head back to the base and when it gets close it switches over to line following and guides itself in like that.

Rather than photo-resistors, use photo-transistors. Also, don’t use a laser, it probably isn’t needed. Instead, use a simple red (or better, IR) standard-brightness LED, with a small lens to focus it about 3 inches away. Put the two phototransistors (with a vertical baffle in between to prevent cross-talk) on the robot, between two largish (experiment here) strips of conductive metal, mounted on springs (or use a couple of strips of spring-steel). These are the charging pads on the robot. On the base station are similar charging pads, lined up with the robot. The spacing distance between the pads will have to be experimented with. Basically, the same idea as yours, except now accuracy (and hence, ease of implementation) becomes less of a concern. Use the photo-transistors to guide the robot in (indeed, this guide circuit could be easily built using individual components, with no micro-controller - its not much different than what Grey Walter’s turtle-bots of the 1940’s used - The robot backs into the pads until firm contact is made (monitor the charging circuit on the robot’s side), perhaps using small rotating and backing up moves to ensure contact. The size of the contacts have to be big enough to make good contact, yet small enough so that a singular pad won’t short the two pads on the base station out. More experimenting would be needed.

This is essentially the method that most self-charging robots have used, both in the past and even today with the Roomba, because it is simple, cheap, and effective. The only thing easier (from a certain perspective; certainly the design of the charging circuit would be a bear) would be a base that charged via open-air induction. Such things are possible, but now you would have to tune an air-gap transformer to work optimally.

I should also note to stay away from using lasers (and possibly high-brightness LEDs) in this regard, as the beam could possibly blind small children and pets; there isn’t anything to be gained from such a system (despite what you would think, using a laser does not automatically guarantee an accurate result - indeed, the accuracy needed could end up being so high as to make it impossible to align accurately without additional components).

This is one of the secrets, too, of quality robotic craftmanship: learn from the past, don’t re-invent the wheel if you can avoid it. It’s the same mantra of software development, and any coder worth his or her salt heeds it. While it is more difficult to put in practice with robotics, if you study the history of the subject, you will see patterns that worked, and patterns that didn’t. Obviously, this is also part of the mindset behind open-source software and hardware; to develop and document these patterns so that others can learn and use them.

Hmm - perhaps there needs to be a “robotic development patterns” book, like there is for software development…? Free idea, people (probably already exists)!

Good luck with the system - it sounds like you will have a fun time implementing it, however you choose to do so. :slight_smile:

Couldn’t you make something like this:

Yellow is the robot.

Blue is gnd red is Vcc black is the charging station.

As long as your charging station was smart enough not to apply the current until the robot was fully docked and properly positioned, I don’t see why not, wortelsoft. The robot could check to make sure there is contact by having the dock switch a “short” across the contacts (disconnecting the power to them), and your robot could sense that short. Once it is positioned (turning, rotating, etc), then it could instruct the charger to switch again. Use a two-way IR beacon system (similar to what was described before, just two way) so that communication via IR could take place, and the robot could tell it to switch, etc.

Hm, i thought about such things yet in a different context… why doing a plug at all? if you have a ground based robot anyway you could use a somewhat big unduction plate at the ground to induce electrical energy? This would highly increae chances of the robot hit the charging station and atually get ‘filled up’.

edit also this ‘applying energy’ only when docked could be made easily controllable by using RFIDs or easier, induction in the other direction (At the edges of the charging plates are circuits that ‘listen’ for a signal from the robot, when it crosses them they start the charger)

While I’ve never done it, I am pretty certain that designing an efficient air-gap transformer isn’t for the faint of heart (or skill - of which in this area I have none), which is what I assume you mean by “induction” charging.

Really, two bare metal feelers or bumpers touching a similar set on the base would both be simplest to build, and most likely to work every time, provided you added some “smarts” to the base to communicate to the robot, so that it both knows how to get there, as well as when it is in position to turn on the charger.

Certainly iRobot could have created an induction charger for the Roomba; they have the capabilities and the resources (read: smart individuals working for them and the money to pursue) to have implemented an induction charger, but for various reasons, they didn’t, and instead went with a simple contact-based charger. I would hazard a guess that among those reasons, reliability and ease of implementation were high on the list.

Also, notice how the majority of electric vehicles rely on contact-based chargers (in the form of “plug into the wall” cords). GM went with an induction paddle system mainly because they were designing for the future (ie, charging stations for the public use), as well as a car with a large charging voltage (IIRC, it was around 3-400 volts) for quicker charging, plus there was a larger safety factor involved with a charger spitting out that much voltage with fairly high amperage capability as well.

For a small to medium-sized hobby robot, an induction charger, while it might be interesting to develop, is probably outside the abilities of many robotic hobbyists simply because of the knowledge needed to develop an efficient air-gap transformer (the number of books that exist detailing transformer design is almost as staggering as the number dealing with steam-boiler design). With that in mind, a contacting base charger is simpler, cheaper, and more reliable to build. I am not saying this to stop anybody from trying, I am just trying to convey that it takes more than a basic understanding of electronics and electricity to implement.

These all sound like good ideas, but sadly i won’t be using any anytime soon. I’m still new to this and gotta build some simple stuff first. One day though, I’ll have a house full of robots going to charge themselves when need be… :slight_smile:


My wife and I own a couple of Roombas; what we have found is that the charging station, while a good idea, isn’t as reliable in practice unless you (by spending a good quantity of money) have multiple charging stations around the house, because the Roomba needs to be near the station to see it. Between that and the fact that we only had a single charging station, one or both of the bots would be stuck somewhere dead, and we would have to manually move them anyhow. For such few, this really isn’t an issue, but I could see it as becoming interesting for more than a few roaming robots in a household. For instance, you would need a lot of smarts built into the robots as well as the chargers, so that one robot knows when another is full, and how to navigate (which room?) to an empty charger. Something else to keep in mind for your designs… :slight_smile:

Of course there will be a whole lotta smarts in them, I;m making them myself :smiley: Good thing i’m not making them now, or else they’d be full of nothing… gotta get teh basics first!

Of course there will be a whole lotta smarts in them, I;m making them myself :smiley: Good thing i’m not making them now, or else they’d be full of nothing… gotta get teh basics first!

Love the attitude, tempered with a bit of reality.