Here I present you with a world-class all terrain vehicle with four wheel drive, all electric, regenerative braking, 5-28 HP(4-20kW), can be built by anyone, and it's all open source!
I have many reasons to make my own ATV, here are a few:
I have weeds. That's whole reason for this. They're so bad that I actually have to spray them. There are so many on my 5 acres(2 hectares) that I can't do it with a backpack sprayer. So I bought a 25 gallon tank and boom sprayer. I put it in the little trailer behind my mower and promptly got stuck on a slope and had to get my truck to pull it up the hill. That was when I decided to look at ATVs and I found all these other cool farm uses for them like plowing, mowing, winches, road graders, etc. Here's a picture to give you an idea:
I have to travel several miles to go back and forth to broken sprinklers and pipes, shut off water, go get parts, go fix it, then back to turn the water on again. I usually have to carry a shovel, wrench, sawzall, pipe, connectors, and a bottle of glue with me to make a repair. So an ATV with all that loaded on it would be a godsend.
OMFG Honda wants almost $10,000 for a new ATV that can haul a 180lb(81.6kg) dude plus a 200lb(90.7kg) spray tank. A decent used one runs about $5,000. That's insane! I might as well get a brand new Kubota 4x4 tractor with a front loader and back-hoe for that kinda money. Polaris wasn't any cheaper.
For $10k you'd think you're getting some pretty fancy atv, right? Nope, it's the same old internal combustion engine and then they nickel-and-dime you to death if you want "extras" like 4wd, automatic shifting, power steering, independent suspension, etc. Also you have to play the "name game" to figure out that you want the honda fourtrax foreman 4x4 ES EPS starting at $8,200. After all that, you get a product that is locked-in to Honda so they can, and do, charge exorbitant prices for parts and then they can discontinue making parts whenever they want; forcing you to buy a whole new atv.
With prices of raw materials and technology at an all-time low, many new technologies out, mass production all moved to the lowest labor cost countries, I figured something must be amiss. Shouldn't a mass-produced atv like the Honda be really inexpensive and high quality? Nope! This is what the end of capitalism and globalization looks like, where low-paid workers can no longer afford the goods and services that capitalists produce. Anyway, ONWARD!!!
I decided I wanted an all electric vehicle because they are vastly superior to internal combustion engines. Benefits include things like 10min charge times, no oil changes, no gasoline, fewer moving parts, longer life, higher torque, etc.
Let's start with the wheels:
I wanted to have the equivalent power of a Honda, about 28HP(20kW), which is great for my situation but for just a fun and cheaper atv you can go down to 4kW. To get this power, I split it up 4 ways and decided on 5kW hub motors for motorcycles. They look like this:
Each motor costs about $400 and add another $50 for tires, for a grand total of $1800 for wheels and motors. This could be as low as $600 total for the lower end. These brushless DC motors should last about 100 years with bearing changes every so often. You can choose any motorcycle tire from street, off-road, to even studded for ice and snow. It's a good investment when compared to everything else out on the market. This also gives selectable 2 or 4 wheel drive, top speed of 50 mph(80kph), and you can get these as a kit that includes disk brakes, for 4 wheel disk braking.
I just matched the voltage of my motors to the voltage of the batteries. My wheels use 72V so I found a 72V battery in lithium ion for $1k. You could use 4 car batteries with a 48V hub too and save a lot of money. Each lead-acid battery at 12V 18AH is $30, for lithium ion they are 12V 20AH for $140/ea. So for $560 you can have 48V 80AH, which is 3840 Watts for 1 hour. But WAIT! these hub motors also act as regenerative brakes, so we can just throw in a supercapacitor and some diodes to get way more drive time and power.
I found a 12V supercapacitor which can deliver 300 Amps and charge in under 2 min. It's $100. I'll just throw it in with the batteries and get a charge controller that knows what to do. I need one anyway for recharging off the house.
We lucked out by going all electric with hub motors. No steering required, we will just use something like a potentiometer to slow down the left or right side wheels for turning. When at a dead stop, it will turn 360 degrees in place. As a bonus, this gives us a primitive traction control system for cornering. We will need a steering wheel position sensor for $50.
A double-wishbone suspension system is a great way to overcomplicate a DIY project and make it dead-on-arrival. Fortunately, we don't need one. Thanks to not needing steering linkages, steerable wheels, or drive shafts, we can use trailing swingarms on all 4 wheels.
We'll use a modular design I found here:
It looks like it's just 4 long tubes that make a parallellepiped with some plates for mounting things. We'll make it big enough to hold all the batteries and add rods to mount the trailing arm suspension and wheels to. I found some titanium tubes for about $20/foot. It looks like I'll need about 16 ft for the 4 sides at $320 plus I might as well make it a space-frame truss by using 0.5" dia for $17.80/ft. I'll use solid titanium rods for the suspension mounts and space the wheels 36" apart so I'll get 72" of 1" solid titanium rods at $5/inch for a total of $360. So we'll probably end up buying $1k worth of titanium. You can probably get all this in steel for under $100. My goal is to handle 600lbs of weight.
In order to get the right geometry, I'll have to wait until I get a bunch of the parts I need and then use 80/20 aluminum to slap together a frame with the geometry I want.
I found these off-the-shelf for golf carts. They're about $400 for a 300A controller.
Banana seat will be bolted to the frame. $30
Ultralight mountain bike handlebars and gooseneck, $20+$20=$40
We might as well go with a full-blown quad-core raspberry pi 3. With the 40 pins we can use it as an alarm system, display controller, data logger, gps, radio, mp3 player, movie player, horn, and have it play user-selectable internal combusion engine sounds like a harley, atv, etc. $35 + $65=$100
Raspberry pi plug and play touchscreen, $60. RGB 800脳480 display @60fps, FT5406 10 point capacitive touchscreen, 70 degree viewing angle. Waterproof case, $10.
High End: $3250
Low End: $1610
As can be seen here, an extremely high-end ATV with titanium frame, lithium-ion batteries, 4wd, and all the bells and whistles costs less than a 20 year old used Honda. It will probably take 5 days to assemble and program plus a day ordering all the parts. If you're not into welding, you can just pay a welder $50/hr, or you can try a bolt-together frame. If you do a bolt-together, use square tubing instead of round and avoid the stuff with pre-drilled holes unless you know they line up where you want.
If you'd like more info or to get involved and help out you can work with me through github here:
https://github.com/Whytehorse/OSATV
If we all make these ATVs and share our improvements with each other, we can all have the best of the best on a shoe-string budget. I benefit from sharing this design when other people contribute their own ideas. One day, someone will come along and decide to make a snow plow that bolts right onto this vehicle, or a winch, etc.
Keep in mind that I am doing this in my spare time. It will take some time for me to come up with the money to order the parts and then more time to assemble everything, test it, and release videos/photos of a working alpha model. Some things I haven't finished working out like the wheel fenders, foot pegs, etc. I'd like to use graphene reinforced plastic for wheel fenders but I'm unsure about the UV properties and how to make it yet so I may just use aluminum sheet metal. For foot pegs I think I can find either stirrups or motorcycle pegs and just mount them to down-tube and t-bar.
I am planning to do future articles with more detail on the frame and electronics so stay tuned and follow me so you'll automatically get updated.
