projects --> solar powered lego technic motorized excavator

solar powered lego technic motorized excavator

a solar powered lego technic motorized excavator.

contents

background
research
testing
construction (and deconstruction)
materials

what's cooler than an infrared remotely controlled lego technic motorized excavator? a solar powered infrared remotely controlled lego technic motorized excavator, that's what. unfortunately, no such thing exists. fortunately, no such thing exists. that is, no such thing exists (at least for me) yet....

click image to enlarge . lego technic motorized excavator.

this is the lego technic set 8043 (motorized excavator). it's powered by lego power functions (lpf), lego's latest battery-powered solution to enhance lego technic sets with things such as lighting and motorized functions. in this particular lego technic set, lpf allows for the infrared remote control of the movement of this excavator to mimic that of a real-life excavator.

background

i'm no stranger to photovoltaic powered circuits. the concept behind using solar power to drive electrical circuits at its most basic is very, very simple. it's so very, very simple i'll diagram it below:

solar panel/solar panels --> battery/batteries --> thing needing electricity

it's truly as simple as that at its most basic. you don't use the sun to power anything directly. you use the sun to trickle charge the batteries being used to power anything.

in general applications, you're using solar panels with ratings at or double that of the voltage of the batteries you're trickle charging. to prevent damage of the solar panels or explosion of the batteries, a solar charge controller is used between the solar panels and the batteries.

research

to solar power a lego set, it's not quite as easy as there are many considerations that must be taken, not to mention all the associated research that comes with them. these considerations should include (but may not be and definitely shouldn't be limited to) the following:

batteries: which type of battery is to be used? take for instance lithium-ion batteries. they require charge voltages to stay within strict tolerances otherwise a risk of explosion can occur. this then requires that a charge controller be used to protect against this.
solar panel: what rating solar panel is to be used? this depends on the type of batteries to be used. for example, lithium-ion batteries must be charged at a voltage higher than their rating, but nickel-metal hydride batteries cannot be charged faster than their standard charge rate. so in one instance, output voltage needs to be heavily considered while in the other instance, output current needs to be heavily considered.
solar panel mount: what kind of rigging/apparatus is to be used? this depends on the type of solar panel to be used. with regard to lego technic set 8043, the lego power functions infrared receivers can't be obstructed to allow for proper operation.

and with all of the above considerations, there's the obvious consideration of weight.

so on and so forth....

after both extensive and exhaustive research, i found that using nickel-metal hydride batteries the best option. they can be easily trickle charged without giving much consideration to over charging or exceeding standard charge rates (in my application anyhow). the lpf battery pack uses six aa batteries wired in series. nickel-metal hydride batteries are rated at 1.2 volts. this means:

1.2 volts x 6 = 7.2 volts

it just so happens that i was also able to find an unframed/uncased 7.2 volt/200 milliamp solar panel. given this solar panel, it makes it very unlikely that in typical scenarios that the standard charge rate of six store-bought nickel metal-hydride batteries would be exceeded. the batteries i've been using have a standard charge rate of 245 milliamps for 16 hours.

this leaves me with the task of constructing both a rigging/apparatus to mount the solar panel and an adapter to interface the solar panel with the lpf battery pack. i've since found a pinout of the lpf plugs and have a plan for constructing a simple adapter for the solar panel to allow it to interface with the lpf battery pack.

testing

click image to enlarge . this is the first test setup i used as proof of concept.

click image to enlarge . this is the second test setup i used as proof of concept. note the addition of a 1n914 blocking diode. this is a schematic representation of this mess of wires (d1 is a 1n914 blocking diode; m1 is a ampmeter; m2 is a voltmeter).

i've also conducted some preliminary testing to put into practice the theory or being able to successfully trickle charge the nickel-meal hydride batteries in an lpf battery pack from a solar panel. this preliminary testing was just proof of concept and wasn't designed to be conducive to taking and logging measurements in a scientific manner. that is the final step in testing so that i can formulate things like average charge time and so forth.

construction_and_deconstruction

construction (and deconstruction)

my first attempt at building this lego technic set failed. i didn't give proper consideration to tolerances and didn't space certain parts properly. as a result, only the drive train worked. this led me to deconstructing about 95% of it and starting over.

my second attempt at building this lego technic set failed too... just not as much. this time, i managed to have all but boom arm working. this led me to deconstruction about 5% of it. after that, everything worked as intended.

materials

the links in the table below are to from where i purchased these items rather than to their respective product pages from their respective manufacturers. i've since long lost track of costs related to this project.

item	quantity
lego technic 8043 (motorized excavator)	1
lego power functions 8293 (motor set)	1
aa nickel-metal hydride batteries (duracell rechargeable battery eight-pack)	1 (6/8 packaged batteries used)
solar panel (leo sales ltd. monocrystalline 7.2 volt/200 milliamp solar cell)	1
1n914 blocking diode	1