Wireless Charger

 
#11

I'd like to jump back to the original post for a second. I feel that wireless charging is likely not the ideal solution to make the charging process more seamless. My reason being is that wireless chargers do not put out very much current, if they do it's likely that the transmitting and receiving coil are very large in size (larger than our robots). Wireless charging with a coil of the size pictured in the first post would presumably take an entire night to charge a 7.4V 1300mAh battery.

That being said, I feel like we as a community are in a good place to be able to try a system similar to the Roomba docking system. You see the new Linkman charger only requires a 12V source to power it. If the Linkman charger was to be attached to an ezrobot (or DIY robot) with two connections broken out (+12V, GND) and then have a Glyph or beacon system to auto-locate the dock, one could create a automatic charging system.

A simple momentary cherry switch mounted on the robot could be used to disconnect the power to the robot once it is completely seated into the dock. Of course you would need to take it off the dock when charged or have the dock kick the robot off of itself. I guess that would make the dock a robot as well Smile.

Anyway, just some ideas. Although I love wireless charging it's just not all that practical for our scale at this moment in time. As mentioned though, I do think automatic charging is possible with a little creativity.

#12

@jeremie,
I like this approach

Thanks,
Frank

#13

@Jeremie
I have to agree, I think I have been watching to many iphone commercials. Why create a complex solution when a docking station would solve the problem.

#14

@jeremie,
I’m going to try to implement your idea.

Just to be sure, it’s ok if the version 3 changer is left connected to the battery, just as long I disconnect the 12v power. I was always under the impression that we needed to physically disconnect the charger when the battery was charged up... unplugging power to charger was not sufficient.

Thanks,
Frank

#15

My charger appears to be 7.4v 1000mah and the battery is 7.4v 1300mah so we are charging at about .75 C. Depending on number of sensors, active actuators etc if you charge the unit while still turned on with existing charger you may actually find you are not charging the battery but actually causing it to go flat and will kill the LiPo (they don't like to go flat). I assume you could probably charge the battery at 2C without to many issues (although LiPo's are prone to go up in smoke for little to no reason so you may want to put battery in a fireproof bag inside bot) . So you could use a high C charger to do the work but again you want to disconnect charger once battery is charged or you could find your bot goes up in smoke if there is a problem. Maybe safer to stick to the .75 C charge and turn bot off before charging.

So I think a possible process could be Robot self doc's . Robot has a Magnetic switch for on off power. The magnetic switch is activated by an electric magnet on docking station so it cuts power to robot turning robot off when it identifies robot is docked correctly. Next a relay cuts in to connect power to charger, when charger detects battery is charged the same relay disconnects power to charger and then turns off electric magnet turning robot on again.

You could use a second V4 controller that is permanently connected to a power outlet to handle the smarts of the relay, magnetic switch etc. Getting the docking contacts correct and detecting when it is docked will be an interesting task as well.

#16

Good point Frank!

I believe from my previous calculations on a fully charged battery it would take approximately 45 days for the battery to parasitically drain backward through the Linkman charger down to 6V. I'll just a test tonight and get back to you.

@Nink great idea to use reed relays and magnets! Genius!

#17

Unless i'm missing some detail a 7.4v Lipo is a 2 Cell battery.
So you need to balanced charger (3 wires) ground and 3.3v for each cell, a 3 cell battery has (4 wires) etc.

DFRobot has a 7.4V lipo with only 2 connectors
https://www.dfrobot.com/product-489.html

I asked their support and is also in the comments:

Quote:


Yeah, this lipo battery has a bulit-in protect circuit. Which could protect the battery from the danger like overcharge and overflowing. It will be more safe in the application.


It seems allows you charge and use at same time. What ever is inside (circuit) is cool tech.

#18

Oh @Nink and @ptp sorry for the misunderstanding guys. The idea is to have the Linkman charger attached to the battery already through the 3 pin balance plug. It would be the 12V barrel jack that would be broken out and attach to the charging base. I wouldn't want to break out the LiPo positive and negative connections at all, that's asking for trouble lol.

#19

@nink
Great idea on using reed switch

I’m going to start testing this

Frank

#20

@ptp I have a few of those batteries (One came with my fat shark FPV HMD and 2 with a headplay HMD). Batteries work great on the development kit as voltage and plug are same.