Solar Powered Beo-Bot

Rob7

Gent's

I have completed my Boe-Bot with ping and wish to upgrade to my next project.
I·wish to run my bot completely solar for my next project.
I have several solar cells model H02202901D,from .http://www.hobbyengineering.com/SectionFS.html
I am somewhat confused on the milli amp's required to run the Beo-bot at 6 vdc. I could not locate this info on the Robotics manual.
I am not sure on how many cells I would need without the correct milli amp draw from 4 AA batteries ?
I have attached the Energizer Battery doc. The bot is using the E91 AA Bat's.
Mabe I am going in the wrong direction, but I wont know unless I ask.

Rob7

Franklin

Your current draw will depend on what you are running (two drive servos, ping, ir, etc. ) I don't know these values but I'm sure someone here can help. You then need to size the solar cells for worst case conditions so you will have enough power for the bot. The other option is to run the bot until it needs recharging and then have it sleep till the batteries (if you included them) recharge or there is enough light to continue.

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- Stephen

Rob7

You'r right !

After some goggle searching, I have to re-think what my completed project will have and power consumtion will be very important. The plans now are for the two constant rotation servos for the Beo-Bot locomotion. One for IR detection, Ping))) and four pan and tilt servos.

Rob7

Mike Green

The main current drain that you have is the servos. With no load on it, a standard servo can draw about 1/3A while moving and as much as 1 to 1.5A peak under heavy load. Your Boe-Bot needs about 6V to work well and that requires either 4 AA Alkaline cells or 5 AA NiMH rechargable cells. I have a Boe-Bot chassis and have mounted an additional single AA battery holder above the plastic ball at the rear of the chassis.

NiMH AA batteries have a capacity of about 2.3AH (ampere hours). In other words, they will supply 2.3A for about an hour before becoming exhausted. They work better when the average current drain is lower though. If you have one servo or another running pretty constantly, you will probably average 1/2A to 3/4A drain which gives you about 4-5 hours of run time.

NiMH batteries in general can be simply charged in about 10 to 14 hours at the 1/10 capacity rate. For a 2.3AH battery, that's 230ma or about 1/4A. You're talking about roughly 7-8V at 1/4A. That's a lot of solar cells and a very long day. With a charging controller that adjusts the charging current based on battery voltage and/or temperature, you can charge the NiMH batteries much faster, but you'll need a lot more current. There are 2 hour and 4 hour charging circuits and they need correspondingly more current. For a 4 hour charge cycle, you'll need probably 2/3A to 1A.

When servos are idle, they don't draw much current, maybe 10ma each. The PING draws maybe 20ma average current and the Stamp itself draws less than 5ma. You're talking about an energy budget of 60ma or so at idle which is something that can be done with solar cells. Jameco has a small solar panel for about $15 with a 3V 100ma output (probably in full sunlight ... much less in average sunlight). You could use two of these to supply 6V to cover your idle current and a trickle charge for the battery. You will probably need a simple switching regulator to boost the solar panel output voltage when the light is low and prevent the batteries from discharging through the solar panel when in the dark.

Rob7

Thanks Mike,
Late last night, I measured the current draw with servo's and Ping))). My current output was about as expected at 480 ma. almost 1/2 amp.

Rob7