Planning is something I generally steer clear of because it sets too many things in concrete. I was also making a prototype with little prior knowledge. Its a bit hard to learn as you go when you have it all planned out.
However, you should at least think about some of these things either prior to, or during construction.
Scooter Frame
Drive System
Wheels
Motor
Throttle Lever
Brakes
A person that is GOOD at welding.
Scrap metal for extra framing
Time...
A brain. (can be useful, although not entirely neccissary.)
Frame
Although I chose to use a scooter that I already had, it was probably not the strongest scooter that I could have used. That said, it has served its purpose as being a trial / experiment scooter. When I get all of the bugs ironed out of this one then I will lash out and buy or make another stronger scooter, then transfer all the bits over.
You should choose a scooter frame that will suit the size of wheels that you are going to use, and one that will support your weight.
Plenty of ground clearance is also good. Make sure you can lean into a corner without the scooter touching the ground. This is IMPORTANT!
Make sure it has room to fit brakes on either the front or rear wheel, and has plenty of room to stand on. Deck length is more important than width because you can always widen it, but it is a bit harder to lengthen it.
Also work out where the motor is going to go, and make sure there is room for it.
Drive
The drive system you choose to use depends on where you will be riding the scooter, and what you want it to do.
For example, if you want to ride it in town and be able to stop for traffic lights etc then you will need a clutch, but if you use it for non-stop cruising or maybe racing, then a clutch is not neccisary.
There are two techniques for driving the wheel:
Spindle-tyre (no clutch)
This is the system that is used on most of the go-ped range.
You attach some sort of 'spindle' to the motor, and rest it on the tyre.
PROS: This is by far the easiest drive system to put on your scooter
CONS: Water or dirt can interfere with the traction between the spindle and tyre causing it to spin on the tyre.
Chain-Sprocket (with clutch)
This is the system used on most (but not all) of the home-built scooters I have seen.
PROS: You can ride it rain hail or shine, onroad or off and you can stop whenever you want to without the motor stopping.
CONS: Bit harder to make than Spindle-tyre. Little bit more fiddly to get right. (but not impossible)
You can use a clutch on either of these drive systems, or not use one at all. Its up to you.
Ratios
The size of all of the moving parts determines the ratio between the motor and the wheel.
for example, I have a 52-tooth sprocket on the rear wheel and an 8-tooth sprocket on the motor. This gives me a ratio of 6.5:1 which means that for every rotation of the wheel, the motor makes 6.5 rotations.
Anyway, the main idea is to get the highest possible ratio. This means you get better takeoff, but a lower top speed.
But who needs to do 130km/h on a scooter anyway? I'd be happy with half that!
Wheels
Deciding on what wheels to use depends on the type of drive system you intend to use.
If you intend to use a chain system like my scooter, then I suggest you choose a wheel size that is close to the size of the sprocket you will put on the wheel. That way, the ratio between motor and the sprocket is very close to that of the motor and the wheel.
However, if you choose to use the much simpler method of spindle-on-tyre, then I suggest you use a larger wheel. This way you increase the ratio between the wheel and the motor, therefore getting more power for takeoff.
The other thing to think about is whether or not you will need a freewheel. A freewheel is a wheel that will coast without moving the chainwheel.
This is only relevant if you are using a chain. If the wheel is able to coast (freewheel) then it reduces the stress on the clutch, by not having the chain move when you are coasting. This could be a good option if you are using no clutch on a chain system.
If you were flying down a hill and decide to turn the motor off, then everything stops turning, except the wheel.
Motor
By far the easiest motor with a clutch to work with would be a brushcutter. This is because there is a spindle comming out the other side of the clutch. This means that you can simply take off the long arm of the brushcutter, and replace it with a tiny sprocket.
Next in line would be the LawnEdger. Apparently these are good for spindle-tyre drive systems because the are so easy to attach.
I used a Chainsaw because it was what I could get for cheap$. It is not the easiest, or best option, but it worked well anway.
Depending on what size motor you can get your hands on, you should look for something in the 22cc upwards range.
I have heard of people using huge motors that were just less than 100cc but that is excessive. Most of the bought scooters are only around 33cc.
I think 45cc maximum or else you will end up with the scooter weighing too much.
Bigger motors have better acceleration, but they use much more fuel.
When you are looking for a motor, think about how you intend to attach it to the scooter, and factor that in. It's no good going and buying a terriffic new brushcutter motor with plastic casing, only to find there is no way to mount it.
Throttle
When you have your motor bolted to the scooter you will want to have a throttle lever on the handle-bars. This is usually not a problem with brushcutters / Edgers because they already have a cable and throttle lever. It is just a matter of replacing it with a longer one.
Chainsaws are more difficult, because the throttle is located to close to the motor.
I will go into detail on this because there might be some brushcutters that use a solid rod throttle instead of a cable.
Check out these closeups
Brakes
I have found that brakes are quite important when I took my scooter for a run recently. Jamming a foot to the ground and 'smoking' a shoe while lifting the front of the scooter off the ground, just isn't as effective as a good set of brakes. (It looks good though!)
Where to put them? Hopefully if your scooter frame has been bought it will either have brakes already on the front & rear, or there will be a hole to mount them.
Personally I think that front brakes are more effective at sheer stopping power than rear brakes, but they both have a purpose, so get both if you can.
I mounted the caliper brakes on my scooter from the framing tube that I mounted the motor on, but most people mount them horizontally off the back of the deck
Types of brakes (Caliper, Cantilever, Centerpull, V-Brakes, Discs, Hub)
If you want to use V-brakes, it is possible to buy the mouting brackets from any decent bike shop, and weld them onto the frame yourself, however caliper brakes are the easiest to mount.
Building
This bit is hard for me to cover in detail because there are so many variants in home-built scooters, I can't cover them all.
Start off by working out where you want to put the motor, and how you are going to mount it.
Then disassemble at least the rear of the scooter and weld on some brackets, or framing to mount the motor on.
By 'disassemble, I just mean remove the wheel, and any other obstrucations like mud guards, reflectors, stands, etc
The motor on my scooter is held on using two stainless steel bolts into the engine casing. These were drilled and tapped (given a thread) and did not previously exist on the motor. They are the only thing that holds the motor to the frame.
Other people I know, used brushcutter motors, and they welded tiny angle brackets onto the scooter frame, and screwed into the side of the motor. This was on a scooter where the motor was side mouted just infront of the wheel.
The framing I used is old square tubing I had lying around.
If you plan on using the spindle method, then I suggest that however you mount the motor, it needs to be adjustable for when the tyre wears down.
Assemble the wheel
If you are using a chain then you need to put a sprocket on the side of your wheel.
Get your 52-tooth chainwheel, and place it on your 12inch plastic wheel. If you are lucky like me then you will find that the spokes on the plastic wheel, match up exactly with the chainwheel. I just used high-tensile fencing wire to strap the chainwheel to the wheel, but a better way is to use bolts and spacers on ALL of the spokes.
If you are using a spindle then, just make sure you have a flat-toped tyre, or at least one that has no knobby bits.
Make sure the wheel has well greased bearings, and that everything is tight in the hub. Not excessively tight, but not sloppy.
You dont want it falling apart while you are riding.
Motor spindle / sprocket
Depending on what drive system you are using, attach either a spindle or sprocket to the motor.
This shouldn't be too much hastle if you are using a brushcutter. Simply remove the brushcutter attachment, and screw on a sprocket or spindle.
A spindle can be anything from a metal pipe with a screw and washer on the end, to a skateboard wheel or boat-trailer roller (cut in half)
Throttle Lever
Hopefully, if you are using a brushcutter, it would already have a cable-based throttle lever. If this is the case, then follow the cable back to the carby on the motor, and replace it with a cable long enough to reach the handlebars. You should still be able to use the brushcutter throttle lever. This is much more sensitive than a brake handle
Brakes
Make sure they work well, if they dont, then rough up the edge of the wheel a bit so they do.
You will need them
Completion
Make sure everything is tightly fastened, and operating smoothly.
Check that the throttle lever doesn't stick when you pull it in all the way
Take it easy on your first test run, because the bolts may rattle loose, chain may come off, etc....give yourself some time to check its running ok before you set off on the great 20km run.
If you have any questions I haven't answered here (there are many), feel free to e-mail me
REMEMBER!
Always keep it rubber-side down, and HAVE FUN!
