Weed Whacker Powered Bicycle!

[Mario]

VIDEO!


I saw one of these on the internet and decided to make one.
It uses a weed whacker engine (one of these) for propulsion. It's 30.5cc and should have around 35mph (55kph) top speed.

I used an old bicycle with good tires and great brakes. I converted the back brake to the throttle and kept the front brakes and coaster brakes.

There's the engine. A 10-year old Echo SRM-3100 weed whacker. The old echo products last a lifetime! It starts on second pull, first when it's warm.

The bike uses a direct drive system, no chains or anything. The spindle is a bike peg with a nice grip made into it so it grips well. You can see at the base of it a small steel plate that holds the peg to the engine flywheel. You can also see the half of a N64 heatsink with the brake cable going into it. The mount for the engine is made of wood and held on by pipe brackets. Several of them.

Here's the brake (throttle) cable from the other side:

It can be screwed in or out to adjust how tight it is.

And there's the control box. At has the start/run switch and an on/off switch for a headlight and taillights. The headlight isn't very bright, it's more for being seen an night that to see. I used a joule thief so the LEDs can be run from one AA battery.

As I'm sure you've noticed, there's no clutch! I couldn't add one because it made the engine about a foot longer. Plus, the clutch is super flimsy, and only made for a nylon cutter. I've heard stories of how the clutch snapped because it's too weak for a load like that, so I left it out.

To start it, you first prime the engine by pulling the throttle a bunch of times (the primer bulb broke). Then pull the choke up and pull the starter cord while holding the back wheel off the ground. Push the choke down, and pull it again and it starts. Then you run with the bike so the engine doesn't stall right when you put the wheel down, then put the back end down and hop on.
Before, I would pedal start it, which is why the tire is balded already.

There is a 13:1 gear ratio so acceleration isn't too great, but top speed is very high.

Any questions/comments/criticisms?

 

[Hifeno]

This is something I wish I had seen when I was a teenager. I had so many weed eater engines laying around then. Oh to be 15 again.

 

[eurddrue]

This is something I wish I had seen when I was a teenager. I had so many weed eater engines laying around then. Oh to be 15 again.

Seriously? You act like you're twelve. I ask a fair price for an item and you say, "I'm never trading with you again! I can get it for cheaper 50 miles away!"

 

[XCVG]

Cool. Not just cool actually, really awesome.

 

[Zero]

Woah! This is sweet! Is this thing street-legal?

 

[AfroLH]

Add a backrest FTW!!!

This thing is Approved!

 

[snowpenguin]

Dude, I commend you. Nice work, love the n64 heatsink!


Is there a guide somewhere, and can you still pedal?

 

[Mario]

Woah! This is sweet! Is this thing street-legal?

Lets's see. According to California vehicle law section 406:

"406. (a) A "motorized bicycle" or "moped" is any two-wheeled or
three-wheeled device having fully operative pedals for propulsion by
human power, or having no pedals if powered solely by electrical
energy, and an automatic transmission and a motor which produces less
than 2 gross brake horsepower and is capable of propelling the
device at a maximum speed of not more than 30 miles per hour on level
ground.
"

Two or three-wheeled device: Check.
Operative pedals: Check.
Automatic transmission: Eh...
Less than 2hp: Check.
Not more than 30mph: Nope.

So I suppose it wouldn't be really considered a "motorized bicycle". I don't know what it is, then.

But in section 5030 about motorized bicycles, it says:
"5030. A motorized bicycle, as defined in Section 406, is required
to display a special license plate issued by the department."

Which it does not do. So I suppose it's kinda iffy.

Dude, I commend you. Nice work, love the n64 heatsink!


Is there a guide somewhere, and can you still pedal?

Sure. Just try googling "weed whacker bike tutorial" or something similar. There's something on Instructables about it, I know that.

 

[Basement_Modder]

Screw the "David's farm" way, I am so making my bike this way now! I have everything in my garage already. I smell a weekend project...

 

[snowpenguin]

Still wondering if you can pedal also... And if you can ride these on sidewalks.


B_M, do you have a guide somewhere you're going by?

 

[Basement_Modder]

Nope. Just put a grippy bike peg on the motor, then mount it with whatever you have on hand. I will probably do what mario did for mounting, unless I weld it. Just add a killswitch and a throttle to the handlebars.

 

[snowpenguin]

N00balert:

"Grippy bike peg" What?

How exactly does the whole electrical side work? How do they control off/on/whatever?

And is it possible to pedal while riding with engine on, or pedal with engine off?

 

[XCVG]

N00balert:

"Grippy bike peg" What?

How exactly does the whole electrical side work? How do they control off/on/whatever?

And is it possible to pedal while riding with engine on, or pedal with engine off?

I think the grippy bike peg is a footrest peg from a dirt bike, could be wrong though.

No idea how the electrical works, probably varies from engine to engine or at least brand to brand.

With the engine on and running, pedaling the bike could be very entertaining. With no clutch, the wheel is coupled directly to the engine (though the wheel is not directly coupled to the pedals). Therefore, you would be battling the engine for speed, and you could back-drive the engine if you are strong enough or if the engine is not going fast. With the engine off, it would be less tense but still difficult because you'd be driving the engine. Because of the peg-drive system, in either situation there is some slip but you also put a lot of wear on the wheel. It is theoretically possible to pedal-start the engine, though probably not a good idea.

 

[Caredo]

I used an old bicycle with good tires and great brakes. I converted the back brake to the throttle and kept the front brakes and coaster brakes.

My only problem with this is this quote right here. I don't see this ending well.

I suggest switching the throttle to the front brake. If only the front brake is usable, you're in for a load of trouble. I remember going downhill at a high speed, then using my front brake, which caused the rest of my bike to flip over and send me headfirst down the hill. The back brake is the best out of the two for actually braking.

 

[themadhacker]

^
yeah that.

 

[Bibin]

Nice mod! This totally undermines my electric one I was working on

 

[Mario]

I used an old bicycle with good tires and great brakes. I converted the back brake to the throttle and kept the front brakes and coaster brakes.

My only problem with this is this quote right here. I don't see this ending well.

I suggest switching the throttle to the front brake. If only the front brake is usable, you're in for a load of trouble. I remember going downhill at a high speed, then using my front brake, which caused the rest of my bike to flip over and send me headfirst down the hill. The back brake is the best out of the two for actually braking.

You know what coaster brakes are, right? They're the "back-pedaling" brakes. You pedal backwards to use those brakes. The front brakes are old anyway, and hardly grip at all. You couldn't flip the bike with them if you tried. They just aid in slowing a little.

But I know what you mean. I had a similar thing happen to me. I would have taken the front brakes out if they really worked at all.

Also, VIDEO TOMARROW! =D

 

[Victim]

How exactly does the whole electrical side work? How do they control off/on/whatever?

And is it possible to pedal while riding with engine on, or pedal with engine off?

From what I can determine. He connected wires to the old stop switch which grounds out the coil so you don't get a spark killing it. Then there is another switch which turns his led headlight on and off. That is connected to a joule thief to allow for one aa.

 

[Basement_Modder]

How exactly does the whole electrical side work? How do they control off/on/whatever?

And is it possible to pedal while riding with engine on, or pedal with engine off?

When the "main power" is off, it just grounds the coil, likely to the handlebars. Its like holding the killswitch down. The other switch just controls lights. My neighbor has a few old chainsaws. May ask him if I can have a motor out of a broken one. More torque=win.

 

[Mario]

Video! It's in my first post as well as right here: