not every idea is a good idea

[jesusgatos]

I went to a bike swap meet on Saturday and I came home with a BOB trailer that I didn't have any particular need or use for, but I picked it up for $30. I was planning on making a simple rack for it, but then I thought I had a better idea. What if I cannibalized the BOB trailer and mounted an engine on a trailer behind a bike?

It would be really neat to have an engine that you could hook up to a bike without needing to make any real modifications to the bike. The BOB trailer attaches with a quick-release to the back axle, and the only other thing I'd need to do it mount the throttle tube to the handlebars.

I was originally just going to mount a little engine on the BOB trailer, but after talking with Robby, we agreed that cutting up a little Honda XR50 was a much better idea (I'm honestly not sure why). Those 50's get about 80mpg though, and they can easily do 40mph. Sounded like a great way to get around town, and I'd be able to ride it on bike paths since it's only 50cc's and would not legally be considered a motor-vehicle.

I looked into this online and found this website. Why hadn't I seen any of these pusher trailers before? What a great idea.

So Sunday morning I went over to a buddy's house and picked up his XR50. I spent the afternoon disassembling it and thinking about the easiest way to attach it to the front half of the BOB trailer.

http://www.trailslesstraveled.com/media/forums/xr50_pusher_01.jpg

I sliced the head tube off the XR50 on Monday afternoon.

http://www.trailslesstraveled.com/media/forums/xr50_pusher_02.jpg

Today I cut the BOB trailer apart, sleeved it to make a new head tube and welded it into place. I took the bike and trailer for a pedal before I went down to the bike shop to buy a longer throttle cable. I was already starting to think that maybe this was a bad idea.

http://www.trailslesstraveled.com/media/forums/xr50_pusher_03.jpg

http://www.trailslesstraveled.com/media/forums/xr50_pusher_04.jpg

I made a new throttle cable using a modified tandem brake cable and length of brake cable housing. Then I partially reassembling the bike (just enough so that it would run), I fired it up and took it for a spin.

http://www.trailslesstraveled.com/media/forums/xr50_pusher_05.jpg

YES, this was a bad idea. The XR50 'wags the dog' so severely that it's almost impossible to control the bike if you try go faster than 20-25mph. Testing didn't last very long. I took it off a sweet jump in front of our house. Crashed and burned.

http://www.trailslesstraveled.com/media/forums/xr50_pusher_06.jpg

http://www.trailslesstraveled.com/media/forums/xr50_pusher_07.jpg

It's really top-heavy and the BOB trailer parts that I used are nowhere sturdy enough to hold up to this type of use. I think the basic idea might work if I mounted the engine (a lot) lower, replaced the BOB trailer parts with heavier-duty components, and added some type of steering damper between the bike and the trailer. Changing the angle of the head tube might make it handle better too, but I'm not sure where to even start.

I think the best thing to do at this point might be to buy a new XR50 frame.

Or maybe it's time to finally build a dedicated XR50/mountain bike hybrid....

 

[stude13]

thats what im talkin about----wow

 

[Large Filipino]

That is so cool. How were you shifting the gears? I think you can stabilize it by going with an ATV axle in place of that single back tire. It's a triangulation thing.

(edit) Wait. Don't allow it to swivel on that what used to be the steering head. Drill a hole straight across that and slide a bolt in there. That should stabilize it.

 

[jesusgatos]

I wasn't shifting gears. This was just a test-run. I was planning to rotate the shift lever up past vertical and use a morse-style cable (push/pull) attached to some type of hand-operated lever to shift. It's an auto, so there's no clutch to worry about. 2nd gear (it's a 3 speed) is about as fast as I felt comfortable going anyway (about 25mph). It's SKETCHY.

I know what you're saying, but I didn't want to build a trailer with an axle and two tires.

 

[Alaskavan]

Or, you could do what I did with a motor like that.

 

[graucho]

Hey there. I dont know if you looked throught these vids, but maybe it will give you a few ideas? Also maybe start from a minibike. See the simularities in the bottom photos. You have a cool looking set up though. graucho

http://www.youtube.com/watch?v=ACTTALCLdl0
http://www.youtube.com/watch?v=EXCEDU0atuw
http://www.youtube.com/watch?v=OHZqxbCqxOo

 

[jesusgatos]

Or, you could do what I did with a motor like that.

Link?

Thanks Graucho, I have seen those videos. Wanted to build something a little bigger/faster/dumber.

 

[graucho]

OK, then lets move to phaze 2. I have a link for this. Rip apart and modify this. 3 years ago I bought 4 of these and tore them down for parts for my other mini choppers. $550.00 shipped. 6.5 hp. auto, oil centrifical clutch, jackshaft, 198cc, 55mph. Heavy duty frame. Motor and clutch run like a dream. I modified the engine, clutch, jackshaft on one, turning it into into a screaming mini. radar at 78mph. With this set up I think you can build something a little bigger/faster/dumber. If your interested PM me.

 

[jesusgatos]

That would make a pretty sweet drivetrain. I think I'm moving on, and will build a dedicated frame for this engine though. I don't really like how the trailer pushes the bike around with a pivot in between the driving tire and the back tire of the bike. There are a few companies making mountain-bike based minibikes using these 50cc engines. I've ridden one of them and have always wanted to build one for myself. Probably won't have pedals though.

 

[Alaskavan]

Jesus, you can find my build here:

http://www.motoredbikes.com/showthread.php?t=7524&highlight=Tadpole

It is a long thread. I didn't start cutting and assembly 'til the 10th page.