For Hackaday By Brad Graham of LucidScience.com and AtomicZombie.com Greets to Hackaday and fellow junk yard hackers! Normally, I would not be sending this type of material to Hackaday because I separate my mechanical welded projects from my electronic soldered projects, but in this case both hobbies overlap. Like many of you, I enjoy building creative things out of whatever materials I can find and use whatever tools are available. When I am out in my garage, I build human powered vehicles, electric scooters, robots, and other mechanical monstrosities that are sometimes difficult to classify. I build these projects for my mechanically oriented website, AtomicZombie.com, and when I am there, electronics is not usually on my mind. When the winter deep freeze sets in here, I move indoors and enjoy building all kinds of cool electronic gadgets such as spy gear, retro video game systems, high voltage projects and all kind of other fun and sometimes dangerous hacks for my other site LucidScience.com. But what happens when the soldering iron and the welding torch meet each other? When you enjoy multiple hobbies, eventually they cross over each other, and in the case of my large robotics, electric bike and scooter hacks, this is certainly the case. Sometimes a large all terrain robot project needs an FPGA controlled vision system, and a Chevy truck differential or an electric bike may require a home built FET motor controller along with a hacked starter motor, so I find myself sharing time between my basement hacking lab and the garage. I am curious to see how many other hackers merge the mechanical with the electronic when working on a project. Even a small beam robot would require some amount of mechanical engineering and although a welder would certainly not be in order, perhaps a small CNC machine or 3D printer would be utilized. I guess the point of this is write-up is that at the end of the day, it matters not if you have wielded a welding torch or a soldering iron as long as your creative energy was released. So this is the story of what happens when my Weller meets my Miller. Sparky V1 - A junk yard minibike.
Sparky was made from a defunct shopping scooter. So, I am at the dump one afternoon unloading a truck full of old 486 mainboards and I see this old granny type shopping scooter sitting in the metal pile. This thing was a heavy beast with 10 inch pneumatic tires, a pair of large 12 volt batteries and a solid square tube frame. The scooter was rusted pretty bad after sitting in a mud puddle for most of the year, but it looked like a good source of junk for a future outdoor robot project so I loaded it on the back of the truck along with as much metal scrap as I could fit in the back. Yeah, I am one of those freaks who comes into the dump with 150 pounds and leaves with 500 pounds! 
Originally, my plan was to make an ROV I tossed the old shopping scooter in my ever growing scrap pile and it sat there until I had a free weekend to spend out in the garage. Usually, I would just start taking something apart and an idea would pop into my head, and I would spend the day building it without any real plan. When I started ripping apart the old scooter, I had the idea to make a small outdoor ROV (remotely operated vehicle) to drive around the neighborhood under remote control and RF video link. I pulled out one of the motors and a batter and to my amazement the motor spun right up, and both batteries were good. The motor was rated at 400 watts and without the gearbox ran at about 2500 RPM, so it was a fairly powerful motor. Within the hour I had also torn down an old snow blower for a few sprockets, bearing and chains and then decided that this motor might have enough power to make a small electric minibike. 
Adding a snowblower sprocket to the rear wheel. At the time I built Sparky, there was no such thing as an electric scooter on the market, so I had no idea of it would even work. The 400 watt motor had a ¾ inch shaft, and it looked powerful enough, but I really had no idea if the minibike would even move a person with a 12 volt battery. I roughly calculated a 20 mile per hour top speed by creating a gear ratio to 1:4 through a 10 tooth and 42 tooth sprocket set I salvaged from the old snow blower. I welded the rear sprocket to an axle and then used a pair of ball bearings from the snow blower to mound the axle. I had found some scrap 1.5 inch square tube at the dump as well, and although it was rusty, it was fine for this project. 
The plan was simple - turn on the motor and go! I took the DC motor to my electronics lab and pulled it completely apart for a good cleaning. I cleaned the commutator and bearings, and then checked the carbon brushes, which looked in good working order. The motor was now ready for service again. I wanted to pull apart the motor controller and hack into the pulse width modulation drive, but since I did not know if this experiment would even work, I opted for a much simpler ignitions system - a contact switch. This hack would require only a brass bolt and a plastic bicycle brake lever, creating a contact switch that sent the current through the bolt and back to the steel handlebars, completing the motor and battery circuit. This system worked quite well, and gave the minibike the name Sparky. Yes indeed, there was a goodly spark each time you pushed the lever down to start moving. 
The frame was built around the battery. The scooter had a pair of large 50 amp hour gel batteries, and after charging them both, they seemed to be in good working order. I grabbed a length of the rusty square tubing and then just started cutting and welding until I had a simple frame built around the battery. I wanted a compact minibike that could be carried in a trunk, so there was just enough room for the battery and motor on the small frame. 
A bicycle head tube is used in the front. The scooter had a set of caster wheels that used bearing components roughly the same size as those used in a bicycle front end so, I chopped up an old mountain bike and created a steering system that worked like that on a bicycle. Now I could use bicycle handlebars as well. Sparky was now beginning to look like a minibike. 
The prototype ready for the first test. I made a simple motor mount and then added the chain drive system, placing the motor just above the rear wheel for maximum space usage. At this point, I just threw on a pair of wires with the lead battery terminal connectors, making a crude hand held switch so I could test the prototype. I dropped a plywood board on the frame, wheeled Sparky out into the street and then jumped into the pilot's seat. I shorted the lead terminal together and with a good crack (and spark), the bike lurched forward, sounding like an electric power tool as I began to pick up speed. To my amazement, the little motor sent me to the end of the block at a speed that would have been difficult to maintain on a bicycle. It was great fun to be moving under electric power, which at the time was unheard of. 
The completed and painted minibike frame. I was so surprised by the performance of the small motor that I took Sparky back to the shop for a full paint job. I made a crude seat out of some old couch material and foam and then added a gusset to strengthen the front of the frame. As the paint dried, I worked out a better ignition system. 
Ready to roll with a new ignition system. I found a plastic spring loaded bicycle brake lever and drilled into the handle to insert a brass bolt. The bolt would contact the steel handlebar tubing when fully depressed, creating a crude high amperage switching system. To control the speed, you just modulate the handle or press and hold it to start gaining speed. The brass bolt prevented any contact welding as the initial blast of current started the motor from a dead stop. The load spark that was made each time the contact was pressed lead to the name Sparky, which was both funny and a bit scar at the same time! The little minibike looked pretty good considering it was made from a rusting heap of junk I pulled form a mud puddle at the local dump. 
Sparky V1 - an electric minibike prototype. Sparky was a huge success considering it was a random project made from nothing but junkyard fodder. I would charge up both 12 volt batteries and Sparky would run for hours as everyone took turns blasting up and down the street and down the back laneway. I enjoyed the little minibike so much that I would often take it miles down the road to the java house or on small grocery runs. The thing was so small that the cops never looked twice, and everyone got a kick out of how fast and quite the little electric vehicle was. So, now I wanted more power! The fusion of electronic and mechanical continues. 
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