Pusher trailer build

[spinningmagnets]

I believe a shorter trailer assembly will be a bit 'twitchier'?, and the longer arrangement would be more stable. If you shorten the length from the bike to the pivot and bring the pivot closer to the rear tire, the power of the trailer will have less leverage to try and push you over sideways when in a sharper turn. I would put a cargo box inbetween the trailer tire and the pivot so the cargo weight would be as low as possible (instead of on top of the trailer tire).

I really like the 20" wheeled version, and easy to increase the power if thats whats wanted later...

 

[Alan B]

You could use a trapezoidal bearing and effectively project the point of rotation forward to increase stability. This is how the Hensley Arrow trailer hitch works. See their website for info on this.

 

[izpirkt]

You could use a trapezoidal bearing and effectively project the point of rotation forward to increase stability. This is how the Hensley Arrow trailer hitch works. See their website for info on this.

Great idea! I have thought of some linkage joints, but have never seen this trailer hitch. Went to the Hensley website, looked at some competing hitches, and saw a Lego demonstration of the joint. I decided to make my own to try to see what would happen with a single wheel. I broke out the kid's Kin-ex and here is the result:

It seems to track pretty well. Rotation of the green "bike" keeps the trailer wheel (white) aimed at a point well forward of the two orange pins on the "bike". This should be aimed at the contact patch of the rear tire, or slightly forward of that. I still am not sure about the push vs. pull and forward/backward dynamics, but I think I'll need a full size demo to get a feel for that.

I'll have to break out the SolidWorks and model up a joint with the right virtual pivot, that fits in the profile of the trailer, and is strong enough to take these forces. Then we'll see what Home Depot or McMaster has to contribute.

I went looking through the forum for "pivot" and "hitch", but did not come up with anything. Lots of the picts on older posts are not working, so I might have missed something.

Has anyone else tried this before?

 

[Rassy]

Your model looks interesting, and would probably work okay on a trailer being pulled. But it looks to me like a pusher trailer would force the trapezoid into an unbalanced configuration that would result in the power wheel trying to push to one side. What happens on the model when you hold the green "bike" back with a little pressure and try to move forward by rotating the trailer wheel? If you set the wheel at an angle to the "bike" does the trailer try to straighten out?

It also seems a little like overkill. I have pushed a bike with both one wheel and two wheel (both wheels powered) trailers and they never tried to high side the bike, even though there was some twitching on the one wheel trailers at higher speeds.

Anyway, I'm just curious. Thanks

 

[izpirkt]

It is amazingly stable when holding the green "bike" and pushing the wheel toward the "bike". The trapezoid does not fold up like I thought it would. The force from the wheel is always pushing directly toward what would be the contact patch of the rear wheel of the bike. I'll have to get either more complex with the model or set up a full size demo to test the dynamics with a two wheeled vehicle in front.

I realize that this does seem complex. But if it offers a compact trailer with no twitching/oscillation/ at high speed or high load, then it will be worth it. The further advantage would be the ability to remove one of the linkages and be able to fold the trailer up beside the bicycle for easier chaining at a bike rack.

Again I will ask: has anyone tried this type of hitch before?

 

[Alan B]

It works amazingly well on my 10,000 pound trailer. Makes towing as calm as not towing, can't feel the wind or semi's passing. But the hitch I have weighs more than 100 pounds so putting it on the bike doesn't seem very practical. If you scale it down it should be fine.

If it works as well on the bike as it does on the RV you almost won't be able to tell there is a trailer back there. In the name of science it certainly seems worth a try.

 

[bobc]

Loving the trapezoidal hitch idea - should be relatively easy straghtforward to engineer too.
Still hoping I'll be able to catch you up some time this week izpirkt ;^)

 

[izpirkt]

So, with the nice weather this weekend, I wanted to take the bike out for a nice trail ride. With the roots and rocks, the trailer would have be impractical, and I wanted some exercise anyway. The trailer came off by removing two bolts, and detaching the throttle and CA connection. These wires were bundled and secured to the bike frame with some velcro straps. So the bike was basically back to normal, with only a few extra ounces.

The ride was a lot of fun, and then this morning it took less than 2 minutes to put the trailer back on, and ride to work. This is the furthest I have taken the trailer from home, and it did great. It averaged about 20 Whr/mi, with some long hills and light pedaling. Just got home from the 2mi/70 degree commute, and no sweat or hard breathing! It would do 18mph on the flats, and still about 12mph on the hills.

Riding on sidewalks emphasized an issue that I'm not sure how to deal with. The trailer would bounce over the seams and irregularities and lose power. I have very low pressure in the tire, so it absorbs a lot of bumps, but when it regularly hits the sidewalk seams, it does start to hop. Adding a suspension could eliminate some of this, but It would need damping of some sort that can be tuned. It has to work with a loaded or unloaded trailer. A 100% potential increase in weight means the damping/ spring force needs a lot of variability.

In addition, it sounds terrible with the whine of the gears fluctuating so much on the bumps. The geared motor is probably not going to be the final solution for this trailer, since the brushless is so much quieter. The brushless may not really be more effective as a device, but will appear so without the noise.

 

[izpirkt]

Yesterday I swapped out the 26" geared hub motor on the trailer for the 20" brushless. Today I rode to work and amazingly the sway at high speed is nearly gone. I think it has something to do with the stiffness of the wheel itself. The spokes on the 20" are only about 4" long. I think that this reduces the side to side springiness that gets the larger wheel bouncing from side to side. I'll have to see what happens when I put my backpack back there and have more mass bouncing around.

I also enjoyed the silence. You can barely hear the motor, at high speed it sounds like a bee buzzing away back there, but the gear whine is gone.

I rode 11 miles today, using up the 4 batteries right as I turned into my driveway. I didn't really pedal all that much, and had some pretty big hills. At 17 Wh/mi, it is more efficient than the brushed motor, and is equivalent to 2058 mpg. My average speed was 13mph, and I peaked at 25.

 

[amberwolf]

The sway is probably partly from the longer spokes (especially if they're not fully tensioned), but is also probably from the different geometry of things putting more mass at a greater height with the larger wheel.

 

[izpirkt]

On a side note, has anyone been able to try out one of these? http://www.ridekick.com/