Weed Whacker Powered Bicycle!

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Mario
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Weed Whacker Powered Bicycle!

Post by Mario » Sat Aug 22, 2009 11:52 am



I saw one of these on the internet and decided to make one. 8)
It uses a weed whacker engine (one of these) for propulsion. It's 30.5cc and should have around 35mph (55kph) top speed.

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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.

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

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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:

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

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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! :P 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? :wink:
Last edited by Mario on Sun Aug 23, 2009 7:40 pm, edited 1 time in total.
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dragonhead
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Re: Weed Whacker Powered Bicycle!

Post by dragonhead » Sat Aug 22, 2009 12:01 pm

i used to build these suckers a few years back! deflate your tire a bit, loosen your motor mounts, push the drive spindle down further onto the tire (so you see noticeable deflection in the tire), retighten the motor mounts in the new position, and reinflate the tire. it should get you better drive system traction. and allow you to pedal start without destroying the tire.

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schmellyfart
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Re: Weed Whacker Powered Bicycle!

Post by schmellyfart » Sat Aug 22, 2009 1:27 pm

Post a video!! :mrgreen:

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Joes2Silly
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Re: Weed Whacker Powered Bicycle!

Post by Joes2Silly » Sat Aug 22, 2009 4:08 pm

I am so building one of these things now. You've got a pretty good setup there :)
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Mario
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Re: Weed Whacker Powered Bicycle!

Post by Mario » Sat Aug 22, 2009 8:59 pm

Video tomorrow! :D

And thanks for the nice comments. It's awesomely fun to ride. :P
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Re: Weed Whacker Powered Bicycle!

Post by Joes2Silly » Sat Aug 22, 2009 11:23 pm

I've done some research, and you could increase your speed if you attach the motor by chain instead of friction drive. But that would actually require more work and another 5-10 mph probably isn't that big of a deal for the trouble it's going to be
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Re: Weed Whacker Powered Bicycle!

Post by ttsgeb » Sat Aug 22, 2009 11:37 pm

Sorry, but that doesn't really take research to figure out.I
Anyways, It's very impressive looking, but I imagine it's a bit unbalanced. It would be great if it didn't have to be pushed to run though, with your setup, it sounds like it's great for cruisin' but not good for getting short point to point distances.
Last edited by ttsgeb on Sat Aug 22, 2009 11:54 pm, edited 1 time in total.

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Re: Weed Whacker Powered Bicycle!

Post by snowpenguin » Sat Aug 22, 2009 11:52 pm

ttsgeb wrote:Sorry, but that doesn't really take research to figure out.
Don't be an ass.
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hackmodford
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Re: Weed Whacker Powered Bicycle!

Post by hackmodford » Sun Aug 23, 2009 9:19 am

Looks slick :wink:

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Mario
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Re: Weed Whacker Powered Bicycle!

Post by Mario » Sun Aug 23, 2009 7:39 pm

snowpenguin wrote:
ttsgeb wrote:Sorry, but that doesn't really take research to figure out.
Don't be an ass.
Be nice.

Also, video:
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cowsgoquack101
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Re: Weed Whacker Powered Bicycle!

Post by cowsgoquack101 » Sun Aug 23, 2009 9:38 pm

Cool beans mario! I always wanted to do something like this I just never had a spare engine laying about. I wonder if a leaf blower engine would work...

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dragonhead
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Re: Weed Whacker Powered Bicycle!

Post by dragonhead » Sun Aug 23, 2009 9:42 pm

cowsgoquack101 wrote:Cool beans mario! I always wanted to do something like this I just never had a spare engine laying about. I wonder if a leaf blower engine would work...
yep.

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Re: Weed Whacker Powered Bicycle!

Post by eagle5953 » Sun Aug 23, 2009 9:58 pm

What sort of MPG rate can you get on this? Range?

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Re: Weed Whacker Powered Bicycle!

Post by ShockSlayer » Sun Aug 23, 2009 10:21 pm

Nice.
http://twitter.com/ShockSlayer" onclick="window.open(this.href);return false;

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Re: Weed Whacker Powered Bicycle!

Post by dragonhead » Sun Aug 23, 2009 10:50 pm

eagle5953 wrote:What sort of MPG rate can you get on this? Range?
who cares? its fun.

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