Stealth Electric Monster Chopper

About: Dan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products.

Fully electric powered monster chopper bike with whopping four-foot forks. An integrated hub-motor and battery packs concealed within the fork make this a snazzy, stealthy cruiser that doesn't run on dead iraqis and keeps the canadian hot-tub market healthy!

The main features of this bike are that we used an electric hub-integrated motor, and we used the front fork as the battery compartment.


metalwork and assembly: saul
battery mounts: dan

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Step 1: Parts!

The key ingredient: The Zappy integrated hub-motor. this is the gizmo that inspired and made this project possible! it's an entire 250W electric motor built into the hub of a bike wheel! That makes it super-easy to build any electric vehicle you want, just attach the hub-motor wheel, battery and controller and you're done - no drive train at all.

These hub-motors are standard equipment on the Zappy3 Electric Scooter ( the entire zappy scooter is about $500, you can scavange everything you need from one of them, or you can order just the hub-motor and electronic controller from Zappy as spare parts, which will run you around $250 i think. The zappy scooter works great, but 3 wheels is SOOOO lame.

The zappy motor is 36V, 250W, and their controller has a key-switch and variable-speed thumb-trigger. By their specs, you'll get about 12 miles on a charge, at a speed of about 12 mph - although there are plenty of options for increasing those numbers.

Step 2: More Parts!

We'll also need a donor bike, if you'll ever want to pedal it use a mountain bike with low gears because this thing is heavy when we're done.

Batteries! the Zappy3 scooter uses a heavy, ugly and pollutin' lead-acid battery: 36V, 10.5Ah capacity. We switched to rechargeable NiMH batteries which are lighter, environmentally much better, and because they let us do our second stealthy move: hide the batteries inside the fork! NiMH D-cells have right around 10Ah capacity, so we used 30 D-cells to get 36V. we got our 10Ah D-cells from for about $6 per cell. make sure you check the capacity of the cells, as there are some super-cheap D-cells out there with much lower capacity (they just stick a AA inside a D-cell body!).

- 4130 steel tubes for the fork: 1.50" OD, 1.37" ID, 50" length. Mcmaster-Carr part 89955K67. The tube ID is the constraint here, anything between 1.35" and 1.40" is ok. the ID needs to be sized so that D-cells with an extra wrap of tape around them will slide in easily but not be loose.

- monster sissy-bar handlebars. i don't know where we picked these up, but there are places on the web selling them, and also banana-seats if you want one of those.

- 16ga steel plate, 12" square is enough

- Plastic tubing: 3 feet length of rigid plastic tube with 1" ID and an OD of 1.3 to 1.35 inch (we used 1" PVC schedule-40 water pipe from Home Depot). also, 3 feet of rigid plastic tube with 1" OD and 0.75" ID (we used nylon tube, mcmaster-carr part 8628K66)

- springs: 4 stiff metal compression springs with OD 1", length 3.5". mcmaster part 9657K142.

- axle dropouts: we used 2 big square nuts, the nuts are 2.4 inch or so on a side and about 3/16" thick.

- 4 plastic soda bottle screw-caps (1" ID), 4 brass #10 bolts 1" long with nuts, 2 steel #10 bolts, 2" long with nuts, 3 steel 4" compression-tube clamps. 4 pennies, wire nuts, cable ties, wire, crimp connectors

Step 3: Tools!

You'll need:

MIG welder, hacksaw, angle grinder, drill.

Step 4: Wheel Dropouts

the dropout is what holds the axle of the wheel. since this is a powered wheel, the axle of the wheel has flats that must tightly fit the dropout to ensure good torque transfer.

Step 5: Weld Together the Forks

in order to get the forks well aligned, make a jig to hold everything straight and square while you weld. the dropouts in particular must be welded at the exact width of the hub-motor's axle (6.125" apart on ours) - put an 8" long threaded rod into the notches in the dropouts, and 4 nuts to hold the dropouts in position.

Step 6: Head Clamp

big choppers put a lot of strain on the headset, you need to make a big clamp to keep everything together. the clamp will slide on over the forks and the donor-bike head-tube, and then clamp down using steel pipe-clamps.

the head clamp has two short sections of split steel tube. these have an ID sized to just slide over the main fork tubes, and then a pipe clamp squeezes them together to lock down the position.

Step 7: Test Mount the Forks on the Bike

should be able to use the original headset from the bike, put it all between the two steel plates, check that everything seems to work mechanically. you can mount the wheel and handlebar on also to check everything. then take the handlebar off again while we work on the battery mounts.

Step 8: Battery Mounts

the batteries go inside the fork tubes! 15 D-cells in each tube.

- wrap each D-cell with electrical tape or shrink-wrap, they will be jiggling around inside the metal fork when you ride, and you want an extra thick insulator between the cell and the tube. if that insulation wears through, you'll short-out the pack and explode it.

- to make a good electrical connection on bumpy roads and to reduce damage to the batteries, the mounts are spring-loaded on both ends.

- the plastic tube-within-tube-with-bottle-cap setup is to hold the springs and contacts in position and prevent the springs or contacts from touching the fork tube and causing a short-out.

- the shorter mount is at the bottom of the fork (wheel end)

- the lengths are sized so there is about 1" of pre-compression (combined) on the springs when everything is put together.

Step 9: Mount Batteries in the Fork

slide everything in, keeping track of which is the (+) and (-) end of each tube!

after everything is in, you can mount the headset back together.

Step 10: Attach the Electronics

we've kind of made a mess of our Zappy electronic speed control, yours will look a lot nicer than this. we just stuck it on the fork with a big mess of cable ties.

we've got an 18V pack in each of the tubes, connect in series to make 36V. make sure you have a fuse in there!

charging: we lost the Zappy charger so i'm not sure if it will work on the NiMH setup. probably it will do a slow trickle-charge, which is the safest thing anyway. you could build or buy a fast-charger but it will probably be a lot of work or pricey. i ended up making my own simple trickle charger that does 1/2 amp, so it takes a day to charge but it is safe and easy, no danger of overheating.

Step 11: Mount Wheel

almost done! mount the hub-motor-wheel to the fork.

Step 12: Go Cruisin!

oh yeah!

now just apply flaming paint job! that will stop the rusting.

mods: add a couple more D-cells to 'overclock' the motor, and a banana seat and rear-wheel pegs for passengers.

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    20 Discussions

    I love your battery compartment solution! I was contemplating using a similar concept using the tubular frame of a bike or motorcycle to store batteries. I see that you have proven the concept! Good work!


    11 years ago on Step 10

    I'm sort of a noob at this, but how exactly do you charge 30 batteries at once...? Additionally, other than the batteries, do you have any idea how much more this might weigh than a non-modded bike? I'm looking at doing your same project but on a regular bike. Probably going to mount the batteries in a weather-proof box on a rear rack or something.

    4 replies

    Reply 11 years ago on Step 10

    you just connect a 36v charger. multiply D cell weight by 36, what else is going to add weight?


    Reply 11 years ago on Introduction

    Sorry to be such a noob again, but where do you get a 36v charger? I mean, I know what you are talking about, just not sure where to get one. I guess my question about the weight was kind of dumb, I could just look up how much one of those batteries weighs. :P


    Reply 10 years ago on Introduction

    If you really want to use NiMH batteries, you can use an Astroflight charger. Look for a 112D or similar. Note that the charger needs 12v to operate, so you'll need either a big 12v power supply, or a car battery and charger. If you're not going to put your battery inside the tubes, though, it would probably be easier and a LOT cheaper not to use NiMH and go with SLA batteries. Yes, they weigh more, but they cost much less and if you don't need to shave every ounce, the extra expenditure for NiMH is not worth it, IMHO.


    Reply 10 years ago on Introduction

    I don't know... maybe that massive wheel looking motor you put up front and all that stuff you added to hold it in place?


    13 years ago

    you can "overclock" most motors to twice their rated volts and thely work fine (just run hot and noisy) ...spend that much money and dont even give it a good pain job???

    1 reply

    Reply 10 years ago on Introduction

    You can't "overclock" a motor; you overdrive it. It doesn't just run hot and noisy, it's useful life is significantly shortened, both electrically and mecanically.


    11 years ago on Introduction

    good work. i want an electric something or other sooo bad!

    haha, that would be soooooo cool. maybe if you had a similar electric system as one of those wind up torches, and something on the wheel. That bike has cool as wheels.


    11 years ago on Introduction

    Oooohhh ! It's nice. I like. Here's a tech-question : Seeing as it's been a while since you made it. Have you noticed any problems with the batteries? Are you charging them Paralell or Serial? I'm asuming serial so How is that effecting batteries and charging? Thinking that paralell charging would be faster and I'm worried about serial charging causing overheating or other problems in the first couple of batteries.


    13 years ago on Step 2

    Lead acid batteries are only polluting if you don't recycle them. There is a very profitable business in recycling them.


    13 years ago

    I have got to make me one of these! I've only got about a 1 1/2 mile commute and if I make it with higher voltage it will be quicker than driving.


    13 years ago


    1 reply

    Reply 13 years ago

    His D-Cells *are* rechargeables. He wanted batteries that he could hide in the forks, instead of having an obvious battery box, and he mentioned that NiMH cells are more environmentally friendly than lead acid batteries. Nice trick!

    Regarding environmental friendliness of batteries in general -- both lead acid and NiMH cells should be taken to a battery vendor at the end of their lives for recycling. Same goes for NiCad and Li-ion.


    13 years ago

    american choppers look out! as always video please. nice work!


    13 years ago

    that pretty neat too bad the motor and such is so expensive. Perhaps i can find a surplus part or find something in a junkyard