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02-08-2012 #31MBc Member
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- Peotone, IL
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pusher trailer design
My point was trailer weight should be ahead of the axle and result in at least 10% tongue weight. (I recommend more than 10% for pushers). I wasn't suggesting adding weight to cure poor initial design. Why ask for trouble? I wouldn't want a pusher at all if I had to add dead weight to it. Properly built pushers have plenty of traction. Why would you risk building a squirrelly, tail heavy trailer if it is unnecessary to get traction? Follow previously successful design principles as much as possible. If you desire to push the envelope for some good reason, you'll know your experiment was at fault if it doesn't work out.
A friend didn't believe the hitch should be high, like at the seatpost. We made a lightweight pusher with a 1.6 hp engine and a 16" bike wheel for my delta recumbent trike. I was taking it on vacation the next day. It was quicker to build his way, he was doing the welding and I didn't want to be "pushy" about it (pun accidental). As I feared, it bounced like crazy, was always spinning and skipping etc. It worked best if the throttle was opened very slowly, but it still bounced from every little seam or pebble on the road. Reducing tire pressure had very little effect. Some would advise adding dead weight. I solved it by moving the hitch point higher by about a foot (the trailer is only about 3 ft. long). The trailer is now trying to "tuck under" the trike which keeps the pusher's tire jammed down against the road. If you think about it, it is actually lifting a little weight off the rear bike tire and shifting that weight to the trailer tire giving it traction without adding additional weight. Of course this weight transfer is happening only when accelerating or when working against a hill or wind resistance, i.e. only when the engine is actually doing some work. It gets additional traction only when it needs it. It doesn't tuck under when coasting.
I hope you can understand how this traction increasing effect could be maximized if there was a spring or shock somewhere in the tongue. This would help keep the pusher's tire tucked under even when unevenness of the road surface breaks the traction. Use a car engine's valve spring (or two) trapped in a tongue made to telescope by using 2 different tubing diameters. A very lightweight pusher would need only a properly placed bungee cord arranged like the tricep muscle that extends your arm. Use the bungee at the "elbow" of the tongue. The object is to allow the trailer to compress itself lengthwise a couple of inches against something springy before it pushes against the bike. My first pusher achieved this fully in the simplest manner possible. The tongue is two horizontally parallel pieces of bent conduit. In the horizontal plane the tongue is quasi-triangulated and stiff, but vertically it is just flexy enough to provide a little suspension for the weight of the engine. Lengthwise the trailer compresses itself a bit due to the bends in the tongue, which bend a little more when transferring thrust from the powered wheel to the bike. Engine vibrations are entirely absorbed by the bends in the lightweight tongue as well.
I don't like admitting it, but I didn't anticipate many of the benefits of my minimal design. I knew one piece of 3/4" conduit wasn't strong enough, so I used two. I made them horizontally parallel because that way was easier to bolt to the horizontal half of my u-joint made from two gate hinges. The other side of the u-joint had to be the vertical side to easily attach to the seatpost. Making the trailer longer added to the suspension effect by increasing flexiness and putting the engine below the line from the tire contact patch to the seatpost hitch. The resultant pendulum effect almost eliminated the need for a u-joint. My rudimentary, sloppy-fitting u-joint made from gate hinges fulfilled its mission. A minibike wheel is what I had and it was easier to use than a bike wheel due to the sprocket being large relative to the diameter of the wheel. (I wouldn't need a huge sprocket or a jackshaft to get a suitable ratio). My choices for simplicity, common materials and no welding worked synergistically to eliminate problems I didn't anticipate. If I named my vehicles, this one would be "Serendipity".
I'm hoping you have read about other pusher builds and are aware of difficulties encountered in building u-joints precise and beefy enough to overcome imbalances and topheaviness. Some gave up and switched unnecessarily to two-wheeled pushers. There are many times when I would prefer to have a single track when I'm on my trike. Getting as far as possible to the right risks having one wheel on the lower shoulder and the other on the pavement. A two-wheeled pusher has the same drawback and only makes sense to me if it's behind a trike that already has the disadvantage of a wide track. Even on a trike I prefer a single wheel pusher for reduced weight and expense and quicker acceleration.
A little, relatively low pressure donut tire is easiest to design for, but for certain builds higher pressure bicycle type wheels can and should be used (ironically mostly for their light weight) and don't require ADDING weight to eliminate their bounciness.
Where are you guys who love your pushers, recognize their basic principles and would like to see them develop? Speak up. Pitch in. Let's hash these things out and see if we can agree on what should be in a sticky. Too few are using the search function. A builder should read EVERYTHING written here about pusher builds. There isn't an overwhelming amount of info yet.
Last edited by Dennis Becraft; 02-09-2012 at 12:09 AM.
02-09-2012 #32MBc Member
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- May 2009
- Colorado Springs
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Hi Dennis -
Thanks for your comments. You brought up some valid points. The telescoping tongue is an interesting concept that I never thought about. I can see the "tucking under" action during acceleration. It makes sense. And the wide stance, where one wheel starts bouncing off the shoulder. . . That would be bad, especially if the right wheel hits a tire rut. . . I could see the trailer go flying.
I also hope guys from the pusher crowd respond. I'd like to hear about their lessons learned. I'd like to keep from re-inventing; that can get expensive and time-consuming.
Riding the bike with pusher without the engine belt hooked up (just being pulled) was just fine, barely noticeable back there. But once powered to push the bike the handling changes & even though it was super lightweight, could be noticeably felt back there.
I'm sticking to mounting the engine on the bike & if need be, pulling a non-motorized trailer to haul stuff.
p.s. the reverse stem mounted front wheel hub hitch works beautifully & as simple as can be, allowing up & down motion & left to right motion w/ no twisting motion...
02-22-2012 #34MBc Member
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- Jan 2009
- Phoenix AZ
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I just got my push trailer running again, think i might hook it up and ride it again.
I love the option of mounting to any bike with a seatpost in 10 mins and riding away.
My fattie 10" tire never had any traction problems and my u-joint pivot works great with no wobble.
I have replaced the pin with a bolt and washers to tighten the u-joint up.
I should take some new pics, its all painted and finished.
Last edited by Gen3Benz; 02-22-2012 at 07:37 AM.
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