48V Electric Flat Tracker




A Bay Area native interested in electronics, mechanics, and robotics, and automobiles. Formerly ...
About a year ago, my dad and I had the idea to convert a beach cruiser bike into an electric motorcycle. We purchased the bike and all the parts necessary and got to work. We modified the frame and rebuilt the bike from the ground up. When we finished, we were extremely satisfied with the results - a 48 volt, 15 horsepower board track racer.

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Step 1: The Components

We started with a Felt beach cruiser because it had the right look. We wanted a beefy bike that could fit all the components. The goal was to keep the center of gravity as low as possible. Here are the rest of the main components we purchased:
- Briggs and Stratton Etek motor (now discontinued)
- Alltrax AXE 300-amp programmable controller
- Magura 0-5K ohm twist-grip throttle
- 4 x 12V, 21Ah sealed lead acid batteries
- Avid BB7 mechanical disc brakes (160mm rotors)
- #35 moped chain
- 13-tooth drive sprocket
- 66-tooth rear sprocket
- big power switch
- 300-amp fuse
- 8 1/4 in. stainless steel motor mount (this replaces the original bottom bracket)

Step 2: Front Fork

We removed the original rigid front fork and replaced it with a Manitou suspension fork. We also bolted on an Avid disc brake set to the front end. We chose to go with mechanical discs instead of hydraulics simply because they are less expensive and less complicated. The Avid BB7's are fully adjustable. You can dial in each pad separately.

Step 3: Rear Brake Mount

Because the bike we purchased used coaster brakes (pedal backwards to stop), we had to fabricate a mount in the rear to accept our other disc brake. We used a jigsaw to cut out a piece of steel for the main shape. Next, we used a drill press to tap holes for the brake.

Step 4: Rear Hub/Sprocket

The rear hub we used is designed as a "dual disc" front hub. It has a standard mountain bike 6 bolt disc pattern on both sides. We took a blank 66 tooth rear sprocket and drilled it to accept the 6 bolt pattern. The alignment of the hub, sprocket, and disc rotor are critical.

Step 5: Rear Drive Complete

Here the brake mount is welded on, the wheels have been laced to the hubs, and on the right side, the seat stay has been crimped to get clearance from the chain and sprocket. The axle tension adjusters we used were from Answer Products.

Step 6: Motor Mount and Foot Pegs

The motor mount (cut from the same piece of steel as the brake mount) is welded into the stainless steel ring and the ring is welded into place, exactly center, replacing the original bottom bracket. The foot peg mounts are made from a couple of old work light stands welded together.

Step 7: Mount: Drilled and Welded

Centering the motor ring is very important. The ring is a section of a stainless steel light post salvaged from a scrap yard cut to 4 1/4 inches wide. It is 8 1/4 inches in diameter which leaves about a 1/8 inch gap around the motor. It is perforated on the drill press to allow air flow to the motor and notched on the right side for chain clearance. The motor mount is welded offset inside the ring for optimal motor shaft and chain placement. Mounts are welded to the underside of the motor ring to accept the removable foot peg assembly. The foot pegs themselves are aluminum BMX "grinder" pegs.

Step 8: Seat Mount

The original seat post was removed, cut short, and welded on the seat stay bridge over the rear tire and a gusset was added for strength. A rubber cap was put over the existing seat tube, and the seat clamp was flipped and reversed.

Step 9: Welding Complete

Here you can see the bike coming together. The beefy wheels and lower saddle position give it a retro look. Notice the brazed on eyelets for the rear brake cable routing.

Step 10: First Assembly

The battery trays were fabricated from aluminum stock. Each tray was then riveted together and bolted to a right and left panel. The panels are then bolted to each side of the frame. Note the power switch in the center. The right and left panels are asymmetrical to accept the terminals on the back side of the power switch. The controller is mounted upside down under the top tube with the terminals pointing backwards.

Step 11: Final Assembly

After we had finished the assembly, we had to wire it up. Within a few hours, we were testing it up and down the parking lot. It really accelerates quickly and we have not tested it for top speed. It is estimated to do better than 50 mph.
The controller we used can connect to a PC via a serial (RS-232) cable. With the freeware on their site, alltraxinc.com, you can view statistics in real time, change settings, and adjust the power curve for the throttle.

Step 12: The Maiden Voyage

This was the first chance we really got to ride the bike to its (almost) full potential. The bike is smooth, quiet, well-balanced, all torque and pretty fast. It's a blast to ride! After finishing it, we decided to call it the EV-12 for various reasons.

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    403 Discussions

    When I talk about instructables to people, I use examples of exceptional work to illustrate it orally to them, yours is one of the ones that tops the list!


    9 years ago on Introduction

    Without a doubt, the nicest electric bike I have ever seen. Amazing work.


    3 years ago

    Setup a headlight, tail light, brake light, and turn signals. That should be all it takes to get it inspectable, and therfore registerable, as a motorcycle here in Texas.

    8 replies

    Reply 3 years ago

    Umm.. In Ohio and I believe most developed 48-States you must have operable pedal/chainset to meet the requirements of a nonlicensed bicycle.

    But dude, I'm w/everybody else - Awesome build !!!


    Reply 3 years ago

    What makes iy desiravle to register it as a motorcycle here in Texas is that its performance would make it a good fair weather commuter vehicle for people to get to work. It's too fast to be rode as a bicycle. A moped must be registered, in Texas, if its top speed is greater than 35 mph. That's uf u remember correctly.


    Reply 1 year ago

    Unbelievable! you Texans gonna let that stuff stand? FEDERAL Law states that:

    750 watts(1-hp) + pedal power + no faster than 25mph. = a legal bicycle - period - in all 50 states...

    Gotit yall?!


    Reply 1 year ago

    In all honesty the regs I was referring to are old. That's what it was in the 80s. Perhaps the Texas state regs line up with federal regs now. I would have to look it up.


    Reply 1 year ago

    Heck, I thought Texas receeded and is now it's own country? ;~)


    Reply 1 year ago

    "It is estimated to do better than 50 mph." Kinda negates the "no faster than 25mph" regulation.


    3 years ago

    I would love this, but in Belgium this would be considered a motorcycle.

    3 replies

    Reply 3 years ago

    It's considered a motorcycle here in the United States too, as it cannot be peddled. Since it can go faster the 25 M.P.H. in most states it cannot be called a moped (and there is still that inability to be peddled issue). Nonetheless, a pretty damn awesome build!

    I'd love to know what the top speed turned out to be, and what the range is. This would make a great around town commuter.


    Reply 3 years ago

    yeah just to pop into the hardware store or get a beer this would be great :D


    Reply 1 year ago

    Or to just raise some eyebrows and make people do double takes.


    Question 1 year ago on Step 12

    i need to know that how you chose the battery amps and the motor wattage and how much torque needed ?


    2 years ago

    What is the average cost to make this bike??


    3 years ago

    Rock on! I'd be curious to see how this could be done with the derailleur system preserved on the rear wheel. I believe that shiftable gears would help increase the efficiency of the machine abs extend its range.

    2 replies

    Reply 3 years ago

    hey mate. I have had bikes between my legs since I could stand up. Still pedalling too. I also worked in the industry for many years. So I offer my two cents.

    Gears are definitely an attractive proposal, but I definitely feel that the derailleur method of achieving a selection of ratios would suffer with aggressive wear characteristics. On the chain and sprockets obviously. This will be due to the side loading of the chain as the chain moves between the different sprockets. (Ideally a chain should run dead straight from the driving to the driven cog. This is called the "chain-line") A modern 9 or 10 speed chain and cluster can wear out completely in a few 100kms of hard pedalling. Even with educated gear selection by the rider. I was renewing my chain every 3 months and rear cassette each 6 months. Daily commute on a slick tyre hardcore hardtail MTB.

    Older style 6 gear cluster and chains last many times longer because the side loading is many times lower. Meaning tolerances in the drivetrain are very slack compared to the latest 10 gear setups.

    Another point to note is that the application of power by the rider during gear shifting needs to be modulated precisely. If your a well instructed or observant rider. You will ease off the pedal (slightly) during shifting down ratios. And increase going up. This aids shifting smoothness. If you choose a internal hub gear system. Sturmey Archer or Rohloff for example. The selected gear won't engage until the rider momentarily halts pedalling input. This can be done so fast it is almost un noticeable. Once your used to it.

    Anyways, that's food for thought. I am not saying that it wouldn't work. It will work But theses characteristics will definatly factor into the performance and reliability of such a system. If there are any derailleur e-bikes running, I'd love some stats. ☺️

    I would opt for a CVT drivetrain I reckon.

    Ride more everyone. ?


    Reply 3 years ago

    Thank you for your reply.

    Now that you mention it, I can see where side loading would be an issue. From the sound of it, perhaps some sort of self contained transmission would be the solution. I'd assume that's what you mean by a CVT .