Let's Make Robots!

Solar Trike

Much thanks to D&G Green Products for their support http://www.dggreenproducts.com/



My team and I are building a solar powered trike for a solar innovation contest. I do not have much information as of now, but i did pick up the solar panels today. I am still working out the finer details. I know i will need some lead acid batteries, a motor, a trike, speed control,  and a charging circuit. If you have any advice, feel free to leave it in a comment :) No i dont get to keep the solar panels, they are the school's :(









UPDATE 11.27.10

I went driving around town looking for an adult tricycle to buy. Well i found a store that sells tricycles but they were a bit steep for a school project budget, but the goldmine i hit was the owner of this store. His whole house runs on solar power, he has made many electric trikes before, he has all the components to do exactly what i need. He is basically an expert in this. I lucked out finding such a person in my town. 

He led me to his back storage where he was able to sell me a scooter which has most of the parts we need for $30. 


The scooter didnt have a chance...


What i needed from it was its control box...




...key switch...


... 36v motor...



and maybe chain and sprocket 



The batteries are shot


The throttle, key switch ( I left the keys at the guys shop), motor, and batteries plug into the control box. This will read the throttle and control the speed of the motor. Easy enough.

I still need to acquire a trike, batteries, and a charging circuit. The last 2 i can get from the guy. Then the building can really begin.



Maybe next year we will do a solar powered unicycle ;)




Update 1.23.11

Well the trike is running on electricity! 

"wait, the last update was when you took apart the scooter and now you have an electric trike?" YES!

The biggest hassle was not building it, that only took 2 days. The hardest part was finding a cheap tricycle, that took months.

The whole thing was basically built with those scooter parts which is pretty cool i think. Motor, chain, sprocket, motor mount, throttle, key switch, and speed controller came from that scooter. The batteries came from another scooter also.

Sorry no real construction photos because like I said, it was built extremely fast. 

The hardest part of the build was the motor mount. The best place to put it was in the back so the chain did not have to be broken (It had no master link). The chain and sprocket is from the scooter since it was made to fit the motor.

You can still pedal the bike also, due to some fancy bike part that I do not know the name of. It is the thing that the sprocket is bolted to and that slips on the axel. (seen below) Basically when the motor is spinning, it spins the sprocket and the axel making the tires move. When you are pedaling, that magical bike part free spins and does not spin the motor's shaft. 


The trike has a shifter on the right handle bar because this is a 3 speed. I did not want to tamper with that so i put the right hand throttle on the left handle bar ( I am a lefty anyway)


Everything else goes in the basket.

you have the key switch

The controller

The batteries costs $5 for all three. They are old but have been de-sulfated so it was a very good deal considering new ones are $40 a piece. They are 12v 12AH and are wired in series.


So there you have it for now. It runs good. Next I need to add the solar panels.



UPDATE 2.13.11

I have the solar chargers now. I bought 3 of them, one for each battery. Next i have to make a cart for the solar panels to sit on and be pulled behind the trike. I will have to change some of the wiring but that should be easy. 


Update 2.14.11

The cart is almost done. 

We had a $20 trike we bought laying around so we figured the back end was good enough to use as the cart. Sorry no photos before it was ripped in half and painted, you can imagine...


The tires where garbage


So with support from the same local bike shop, we had all new wheels, tires, and a shaft lended to us for the project. We shouldnt need the cart after we give the solar panels back, unless some one wants to donate solar panels :). 

So in the end, with a shiny coat of paint you have this

Wheels still have the price tag on them


Next the trike has to be hitched to the trike, but here is an idea of what it will look like. Bars will run across the cart to hold the solar panels. 


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Yes the trike will carry 1 passenger. This is also an experiment which requires that the battery be able to be recharged by the solar panel as it is being driven around, to test how much longer we can drive it. I am wondering if i can make my own motor controller, this looks like it might be useful in making one if i am correct http://www.sparkfun.com/commerce/product_info.php?products_id=10213. I dont think the motor will be over those specs. 

sorry I dont know enough about that.   instinctively I would lean towards a relay, and I would be happy with on/off, like a motorized wheelchair. 

I'm assuming its a contest... what are some of the requirements of the contest?  who can go the longest and fastest, etc?    how will the winner be chosen?    do you have to buy the remaining parts yourself, or will they provide those also with a cost cap?    and size limits?

if would be cool if the solar panels were always pointing towards the sun regardless of direction of travel.   spinning overhead, or be on 4 posts like a covered golf-cart, giving shade to the rider, tilting 1 way or the other, in real-time.   :-)


its a innovation contest where you can make what ever you want using solar panels. So most innovative will win i guess but it also involves the presentation of it. The parts all have to be bought by the team, this sucks. 

But i am also doing this as a science project, killing 2 birds with one stone. The science project is where i test to see how much longer it can drive with solarpanel+ battery than just battery alone. 

I do plan on having the solar panels provide shade as well :)

the battery I have in the pictured battery box is the largest I could find, and is an L-30, which is about 200ah capacity.   charging at 14.4v, it only takes 2.5a no matter how much panel I threw at it.

solar panels outperform theyre ratings in good sunlight.  as I recall your panels are rated almost 5a, so you'll probably get closer to 6a/ea.   so if you can run a 12v motor, you'll generate 10-12a with panels in parallel.  or a 24v motor at 5-6a with panels in series.   and you would be able to go all day with those panels with either motor/panel config, and then go into the night with the battery(s).   

of course now you need to know how to size the motor, based on total trike weight expected, with rider, 250 lb?

have you made any decisions on 12v vs 24v or motor size?

hmm running all day would be interesting...

Yeah 250lb sounds like something good to shoot for to account for some one who might be heavier to make it more realistic when it comes to others riding it and not just skinny teenagers. 

I have looked up some motors and am still deciding what motor will do. I havent seen very many 12v motors for an application like this. Definitely looking for motor recommendations that will help me decide what to go with, and something that has a some speed controller that matches it or maybe one that could be made would be handy. Im thinking making my own speed controller would be a cool part of the project.


I used a motor from a mobility chair for YardGnome, and it has no problem carrying my weight and more. This is a single 24V motor. It even has an electric brake attached.

I found that if I searched persistently on craigslist, I could find someone listing a mobility chair for under $100. Many of them are the single motor type where the steering is done by the front wheel. It is harder to come by a cheap two-motor differentially steered chair for cheap, but maybe you'll luck out.

motor sizing tools


also GlobalIndustrial.com DC motors.   they have a wide variety of dc motors


essentially you want to disect an electric wheelchair,,,, or one of those Mobility Scooters for the elderly.   perhaps get a spec.sheet to learn how it's rigged.

(using your words :-)  whats a skinny teenager - 125lb ?   you could easily have that much also in structure by the time you include those panels (which I bet are 25 lb/ea), plus 2 batteries (assuming 24v), motors, frame, etc.    my big 12v L-30 battery has to be 50-60 lbs.

if you only find 24v motors, then running all day assumes 5-6amps is enough, (125-150watts).  I suppose if you gear it right, you can acheive motion at some speed with those parameters.    speed control might be a luxury.      you need some theoretical calculations such as how many watts or horsepower is required to move 250 lbs, etc.   1hp = 750watts approx.   so perhaps you need 1/2 hp, motor, or 1/4 hp, etc.  750w x 1/4hp = 175w load service, which is right in line with what your panels will produce in series.   (I'm a little weak on motors and torque).

I guess you need to start by knowing what your current load would be.   those panels are producing 4 - 5 amps in sunlight, so you may not even need a battery (minimize weight).    but if you do, then you want a deep cell marine battery.   like car batteries, they're rated for 12v, but you charge them with 14.4v like the alternator in a car.   unlike a car battery they are designed to be charged and drained over and over, whereas a car battery is shot if you do that 3 or 4 times.

you can buy a simple charge controller for under $50.

make sure you have a diode between the solar panels and the battery to prevent the panels from draining the battery in darkness.   sometimes they are built into the junction box on the back of the panel, but not always.

whether you connect the panels (and batteries) in series or parallel will be decided based on the motor requirements.

treat charging the batteries, and using the battery to drive the load as 2 seperate things.

size of the battery will be determined by how long it needs to provide current absent the sun, or plus the sun, etc.

put a fuse on each panel and each battery.

how big is the trike?  will it carry one of your lucky team mates?

my avatar is a project that does most of what your talking about, without the trike however.

What if you accidentally "broke" the panels, thus you might as well "throw them away?" Tax-write off for the school perhaps? There's a scheme somewhere...