Blog post 58 Written :01-16-2023 Uploaded: 05-19-2023
I do a lot of stuff. I write, sure but among other things, I wrench on old 4×4’s and occasionally I like to go out into the desert and beat them up. As an adult, the people I once did these things with, either don’t have the time, or the desire to go off and do these fun things, or at least not at the same time when I am free to go off and do these fun things. So I am usually four wheeling alone. Big no, no, I know.
So with out another vehicle to help me, I cant get stuck, and with out a spotter to point at things for me, I have to get out and look, to walk the trail myself. But if I am going to crawl a twenty mile trail, I don’t have time to both crawl over twenty miles of rocks and boulders at three MPH in addition to having to stop, get out and look, walk the trail. Liable to walk 15 of those twenty miles looking at and evaluating obstacles.
This isn’t a new problem, at least not new to me, and ages ago, back in high school, I had the brilliant idea of building a go kart, small enough to fit in a back pack, and light enough that it could be carried in a pack over a substantial distance. Miles of rough, broken terrain that is most accessible, only on foot.
Fast forward a decade and a few, and now, I work for a private engineering firm, designing stuff with cad software, building things with 3-d printers, doing wiring, making and reading prints and so on, you know, the usual. So now, I am revisiting my idea, and working on desisngs for it so I can acctaully try and build the thing, because it would be of actual use to me, help me over more ground, faster while wheeling by myself. So this post, is just… a public journal? As I put thoughts to keybaord and work through the design for myself. Figured I might was well share it. I think it’s cool, maybe someone else will too.
So to start with, before anything can be designed, we must know what it needs to do. Here goes…
It must be wheeled transport, capable of transporting a 6 foot tall, 200 pound man, probably with back pack and gear/ water/ tools/ equipment/ spare parts over land. Not just on flat, level dry pavement, but over rocks, sand, grass, where there are no roads, no trails, no path. It must have appropriate tires, wheels, and suspension articulation to perform service ably under off road/ cross country conditions. It must be of sufficient power and strength that it can handle this, that it will not break, that it will not become a liability itself. It must be small enough that it can be carried, for when the terrain gets too rough, it can easily be carried, over some distance, hundred of yards if need be, arbitrarily we will put a maximum weight specification of 40 pounds. To help achieve this, it can not use a gas engine, gas engines are loud, they are hot, they require fuel, fuel that can spill and make mess, and damage other equipment. Therefore, it must be powered with electric motors and batteries. Batteries are also a liability. The batteries must be of a common, readily available size, that can be recharged in the field, either from auxiliary power output from my 4×4, with solar panels, some sort of manual crank charger or preferably, by multiple methods. Another limiting factor are the dimensions of the thing. Not only must it be light enough to carry, it must be small enough that it can be carried, it must be small enough to fit in the back of my 4×4 and not take up to much space that should be devoted to other equipment such as tools, parts, spare gas, food, water spare tires etc. So in addition to the 40 pound max weight, the rechargeable electric drive train and the need to carry and readily move 250 pounds we are also adding dimensional constraints of 48inches L x 24 inches W x 24 inches H. More importantly, if not most importantly. It must be cheap.
My original design, was using some 24 volt DC 350 Watt electric motors from amazon cost about $30 each. But 350 watts isn’t a whole lot. 1 watt equals roughly .001341022 horsepower. So my first design was a 6 x6. Six wheels, six wheel drive. With six motors it was only like 2.8 horsepower. That’s not enough now is it… I started looking at the weight of things.
Four pounds per electric motor, five pounds per battery, and with 2 twelve volt batteries per motor, that’s 12 batteries, and then using 30 feet of 1 inch 16 gauge square tube to build the frame and A arms. That weights .827 pounds per foot. And then sprockets and chains for all six wheels to be driven by the motors. Then six 10 inch tires, with 6, 5 inch wheels. My weight quickly made it well over twice my 40 pound max weight. And that still doesn’t include suspension components, or steering linkages, battery controllers, brakes, etc.
So, I have gone to a separate design I had, the design I originally started with back in high school. Which has three tires, two in the front, one in the back. I have to do the math, and look for different motors and battery options but updates to follow. It will certainly be lighter, with one more powerful motor to drive the rear wheel. With only three wheels instead of six, with one sprocket and chain instead of six, with three shocks instead of six, with one steering linkage instead of two (my original 6×6 was intended to have four-wheel steering for both front and rear pairs of wheels.)
I have been looking at smaller motors and perhaps 3d printing housing and linkages for a small two speed transmission to have a normal, and super low gear ratios for crawling, to get enough grunt out of either a single electric motor of the 3000 Watt variety, or perhaps, what is more likely three very small motors like Maxxis 775’s from RC cars with smaller lighter Li-po batteries. Because having enough batteries to run a 3000 watt motor will get heavy fast.
What I really need/want is a fully sprung, folding, recumbent tad pole tricycle with an electric hub for the rear wheel in addition to the standard 24 ish speeds for the pedals. But those bikes are expensive. Finding one for under $1000 is hard, much less an off road bike with suspension, or an electric hub, or that folds, much less all three of those things combined. So there in, is my last design limitation, materials to build the thing, must cost me less than $1000.
I’ll let you all know what’s happening as my design and build continues, or perhaps, I can find the right bike to fill the roll instead. Stay hungry.