New trailer pusher project started

Discussion in 'Push Trailers' started by Gungatim, Jan 28, 2009.

  1. Gungatim

    Gungatim Member

    After having built a couple of 80cc HT bikes, and seeing a few modern as well as vintage pusher designs, I decided it would be fun to build and ride a bicycle pusher motor.

    Step 1 was to make a list of the advantages of this style motorized bicycle over the 2 cycle Happy Time versions

    They are:
    Little to no modification of the bicycle
    Can use a better grade of bike with shocks for smoother ride at speed
    Can Use a multiple speed bike for easier pedaling when needed (if engine stalls or runs out of gas)
    Use better brakes, front and rear instead of coaster brake.
    Ability to use one of the cheap, plentiful 5hp B&S motors I have laying around.
    Engine will be 4 cycle, no mixing gas (can fill up anywhere), and very reliable.
    Easy to remove if needed, and can also be ridden as a bike easily when out of gas.
    Less noticeable, looks like a small trailer being pulled.
    Can add a rack on top of the pusher trailer to hold a basket for groceries and stuff.
    Uses a centrifugal clutch, no clutch lever or holding in clutch to pedal and start.

    Cons:
    Longer and heaver than standard bike
    May be less stable around curves/will motor push straight?
    Doesn’t look cool like an old fashioned motorbike.
    More likely to get pulled over by police?

    Given all the benefits, it was an easy decision. In addition, because I have so many of the parts already needed on hand, it was easy to design a plan around my stockpile of junk.
     

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    Last edited by a moderator: Feb 19, 2009

  2. Gungatim

    Gungatim Member

    Most of the above pile of engines came from the trash or yard sales. Snow blowers in the summer are a great source of engines, weedwacker’s are plentiful, and most of these only need carb rebuilds or minor tinkering to get running.

    After looking at the many examples on the web, I noticed that these are usually very simple setups, comprising of an engine on a small frame, directly connected to a small go-cart type wheel via a centrifugal clutch. Not much else to it. The hardest part is designing the bicycle mount to motor pusher. It needs to allow articulation in two directions, both vertical and horizontal. Many of the designs I have seen use a long piece of pipe extending up and over the rear wheel with some sort of connection to the seat post. This is how many bicycle trailers are designed, and I never really liked the looks of that, and I have read reports of set tube cracking due to weakness here. Instead, I prefer to mount the pusher low, perhaps to the rear forks somehow.
    My design will incorporate a piece of 1 ¼” strapping, bent in a hoop which extends from one side of the rear fork to the other, around the wheel, and connected through the rear axle bolts. This hoop will stay on the bike permanently, and a quick connection will be added for the pusher motor.
     
  3. Gungatim

    Gungatim Member

    For articulation, it makes sense to use a U-joint. Instead of buying one, I decided to fabricate one out of some short pieces of ½” black pipe I had on hand. Two 2” pieces were cut and welded together to form a cross. Packed with grease, a pair of 5/16 bolts fit nicely through the pipe and will allow easy connection points to both the bicycle hoop and the trailer frame. I may possibly substitute a removable pin to make unhooking it easier.
    [​IMG]
     
  4. Gungatim

    Gungatim Member

    Fore the drive train, gearing is critical. The tire and wheel combination I have measures 11.5” tall. Unfortunately, the wheel hub is for a solid 1” axle, so it will need to be replaced with a bearing hub with sprocket flange. I already have a clutch for #35 chain to fit a standard briggs engine, and this has an output gear of 12 teeth. Using the 3600 rpm of the motor, the 11.5” tire height, and a desired top speed of around 30mph, my hand dandy gear calculator tells me I need a rear sprocket of 48 teeth to achieve a 4:1 ratio. Unfortunately, a sprocket this size for #35 chain is only available in a split style, and would not have a standard Indus bolt pattern. More commonly available is a 60 tooth steel sprocket in the proper pattern, and it is cheap too! With this sprocket I will have a 5:1 ratio, yielding a top speed of 25mph. This should be plenty fast for a bicycle, but if not, removing the governor would give enough rpm at 4400rpm to hit 30mph without stressing the motor much. See below picture for the parts I have on hand to work with.

    [​IMG]
     
  5. Gungatim

    Gungatim Member

    Now that the gearing is figured out, I went ahead and ordered the sprocket and hub needed to complete the project. Total cost including shipping was $48. Manufacturers Supply had everything in stock, and the order not only shipped the day I placed it, but was delivered two days later. Now that’s service! Once the package arrives, I can begin assembly. In the meantime, I will get the frame welded and ready for the wheel.
    The frame design was to be simple; I planned to buy an engine mounting plate, flanking it on both sides with some 2” angle iron which would extend far enough past the plate to allow mounting the wheel in between. This is similar to the frame I made for my scooter project. However, in my vast piles of scrap, I found what appears to be an engine plate, already flanked with angle iron, and extending from the front is a 1 ½” square tube for a Reese hitch. What this was originally used for is a mystery, but it will serve quite well as the basis for the pusher frame.
     
  6. Gungatim

    Gungatim Member

    Once I began laying out the pieces, it was evident that mounting the wheel directly behind the motor would not be as easy as first thought. Unless I used a jack-shaft, the output gear from the engine would not line up with the gear on the wheel. Offsetting one or the other would be necessary, thus complicating the build. Further, being weary of traction and wheel hop, this design does not place much weight on the wheel itself. As a result, I decided to re-design the frame with the motor directly over the wheel. This should put the engine weight where it can do the most good. Unfortunately, the Reese hitch engine plate would not be used after all.

    I designed the frame using 1 ½" angle iron, salvaged from a bed frame. I usually find these at yard sales for a dollar or two, and always pick them up whenever I can. They are a great source of fabrication material, albeit a little work is required to grind off rivets and brackets. The frame itself is basically two rectangles, each 14" long by 8 ½" wide. This allows 7" between the angle iron for the wheel/sprocket assembly. The two rectangles are then welded one on top of the other, with 7" sections of angle iron between them. This allows plenty of vertical clearance for the wheel as well as allowing room to switch to a taller tire in the future if needed.
    http://i105.photobucket.com/albums/m238/tschubeck/pusherframe.jpg
     

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  7. Gungatim

    Gungatim Member

    The above picture shows the completed frame assembly, with the wheel loosely mounted so the engine can be lined up. The axle for the wheel is simply a 5/8" x 10" bolt, centered in the frame. Drilling the bed frame was not easy, as this steel is very hard. Once I drilled up through ½", I ended up using a file to grind out close to 5/8" so the large drill bit had an easier go of it.

    http://i105.photobucket.com/albums/m238/tschubeck/pusherframe1.jpg
     

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  8. Gungatim

    Gungatim Member

    The engine is currently sitting on plywood; however, once the alignment is set, I will weld in a couple of straps for the engine to bolt to. After this is complete, a bracket will be fabricated and welded to the front where the u-joint can bolt in.



    Thinking through how this will work, it has become evident that there will need to be a way for the bike and pusher to stand on its own while the engine is pull-started. In addition, while the engine is warming up, the unit needs to be securely braked so the clutch doesn’t kick in and take off without a rider. This would be easy to accomplish if one were sitting on the bike holding the brakes, but since I will need to be behind the bike starting the engine and fiddling with choke, etc, this will not be possible. To accomplish this needed safety feature, I am thinking of adding a pivoting center stand to the pusher motor frame. Similar to a moped or motorcycle, the stand will lift the pusher completely off the ground, allowing the rear wheel to spin free, and providing side-to-side stability of the unit. With the U-joint pivot in place, the bicycle itself can easily tilt and rest on its own kick stand. Once the operator has the engine started and warmed up, he can get on the bike, hold the brake, and then begin pedaling. As the bike moves forward under human power, the pusher motor will drop off its spring-loaded center stand making contact with the road. Accelerating the engine will then fully engage the clutch, allowing the pusher to take over powering the bike. Sounds great in theory anyway…
     
  9. Gungatim

    Gungatim Member

    The next obstacle is a throttle control. The rider will need some way to control the engine speed from the handlebar, while allowing flexibility between the bike and pusher, as well as easy disconnection when needed. Not sure how I will accomplish this yet. First obstacle is the handlebar itself. The bike already has a twist-grip shifter, as well as brake caliper on the handlebar. There will not be a way to add a typical twist throttle without losing the shifting function of the bike. Instead, perhaps a clamp-on thumb throttle similar to a snowmobile would suffice. Looking though my bike parts yielded a clamp on thumb shifter from a 3-speed. This should be easy to use as a throttle, and will use standard brake cabling as well.
    Stopping the engine will also be necessary. A clamp on toggle switch can easily be wired to the handlebars to ground the engine when stopping. Again, a method of quick disconnection at the rear will need to be devised.
     
  10. Gungatim

    Gungatim Member

    The engine I plan to use seems to be in good shape. Purchased from a yard sale for the princely sum of $7, it was missing the flywheel cover and recoil starter, as well as a sparkplug. Unfortunately, this engine is the newer style which does not use the one-way Sprague clutch on the recoil, but instead uses a cup. Since I don’t have an extra cove of this style, I had to turn it over using some rope. This procedure verified strong compression as well as the existence of spark. The crankcase appears to be drained of oil (not a good sign), and the tank smells of old gas. Hopefully, this engine will be a good runner. If not, a rebuild may be in order.
     
  11. macarollo

    macarollo Guest

    Interesting design. I don't think I have any problems with wheel hop with my design, but I really doubt you will with your setup.

    I never take off from a stop using the engine... I always pedal to 8-10 mph. I am guessing mine might hop if I tried that.

    Your design is top heavy, I wonder how that will handle around fast turns.
     
  12. ZnsaneRyder

    ZnsaneRyder Member

    Mine is top heavy too. I had to have a tightened trailer hitch, and two wheels to keep mine from tipping over and throwing me off the bicycle. I'm curious as to how that will work with one wheel.
     
  13. Gungatim

    Gungatim Member

    Interesting point about being top heavy. I hadn't really considered that. A couple of things I suppose I could do to mitigate that: 1. play with the hitch setup, perhaps move it higher on the frame, or add an arm for stability. 2. extend frame and move engine down and behind the wheel, could then use the top part of the frame where engine was for a basket to hold groceries or lost hubcaps I find...

    Will have to test it on the road and see what it actually feels like. I will be working on it again this weekend, hope to have it attached to the bike. Unfortunately, we still have like 40" of snow on the ground here with lake effect dumping on use for the next few days...I hate winter...
     
  14. brendonv

    brendonv Member

    nice trailer man. Lookin forward to seeing the finished product.
     
  15. Gungatim

    Gungatim Member

    Updates

    I worked a bit more on the pusher project this weekend, and got the engine
    installed.

    [​IMG]
     
  16. Gungatim

    Gungatim Member

    I also worked a bit on the bicycle frame as well. I used some 1/16 angle stock to make the frame around the rear tire. This simply bolts to the frame using the axle nuts that hold the wheel on.

    [​IMG]
     
  17. Gungatim

    Gungatim Member

    To increase stability and keep the frame parallel to the ground, I decided to add some braces. Using some ½” EMT conduit, I bent a 90 deg. On one end and mitered the other end to match the frame angle.

    [​IMG]
     
  18. Gungatim

    Gungatim Member

    Using a 1 1/8” U-clamp, I fashioned a bracket which connects to the U-bolt and is welded to the EMT. This adds considerably to the stability of the frame while not looking too ugly or “tacked on”.

    [​IMG]
     
  19. macarollo

    macarollo Guest

    That looks great. Can't wait to see the finished product.
     
  20. Rgvkid

    Rgvkid Member

    I have a feeling your going to have a tuff time with the trailer setup. With the weight of the engine so high, you will definitly feel it pulling against you in the turns and it will put Alot of stress on the link. I could be wrong, but in theory, it looks like an accident waiting to happen. Plus, the engine is going to have a longer distance to fall and more likely to get damaged if it tips over. Better to stay tried and true with keeping the engine as low as possible for a lower center of gravity. But I could be wrong. Keep us posted.
     
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