In an ealier thread I said I'd document the push trailer I've built, and this is it. 
I wanted a push trailer as it is moveable between bikes and easily disconnectable. Its main purpose is to assist in commuting to work, a 24km trip each way (48km per day).
I got inspiration for my design from the extrawheel, which looks like a great product. http://www.extrawheel.com
First of all, I was dead set on having the attachment point at the rear axle, not the seatpost. Too much force trying to push the bike over when going around a corner under braking or motor power if hooked up at the seatpost. After some stuffing around I decided to use bob trailer skewers - it wasn't worth the hassle making my own. I make my own forks to attach to the skewers though.
Frame of the trailer is made of some scrap angle iron I got from work. Originally I just used the angle section, but it wasn't stiff enough so I had to weld more on and turn most of it to rectangular box section.
For the pivot point I just used the fork and headtube from an old kids bike.
You can see a set of wheel dropouts half way along in the last photo above. I originally had the trailer very short - as per the extrawheel - but I had problems with stability. The trailer would develop uncontrollable wobbles. Changing the frame to box (as mentioned already) greatly helped (increased stiffness), but the problem was still present. I think the problem was due to the pivot point being almost exactly mid way between the trailer and rear bike wheels. Kinda formed a standing wave pattern, that when started, tended to feed itself rather than die down.
I decided to move the trailer wheel back, and as I was going to do that might as well move it far enough to put the battery in front of the wheel, instead of hanging off beside the wheel like originally planned.
Battery box is an ammo tin with some strategically placed foam.
I'm using a Ping 36V 15Ahr battery. I wanted it in a form that is protected from mechanical damage, whilst still easy to carry (charging at work). I spent some time considering and looking at possible cases etc until one day I noticed a 5L green fuel can. I had seen red ones and stuff before, but when I saw the green one I couldn't resist. Green energy!
Foam on the sides and bottom, with a little breathing room above. Sealed back up with hot glue (surprising strong).
It works and looks perfect! 8) 8)
My motor, geared brushless no freewheel, along with some initial problems, is detailed here:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=9891
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14988
Controller is a 350W ecrazyman.
Overall the trailer turned out a lot longer, heavier and more cumbersome than I had originally planned. Despite this it works very well and is easy and stable to ride. Without the pannier it was a little jumpy/skippy on rough roads, and the drive tyre was wearing very quickly. The small amount of extra weight (which I hated having on my back anyway) seems to really keep it on the road and it doesn't skip now unless riding over a really rough section. 26" trailer wheel means it rolls easily and has common spares with the bike.
I've ridden to work about 15 days now - which would be over 700kms. The ping battery has been flawless. I think it is less than half discharged on arrival at work based on charging time. The original charging connector on the battery broke due to bouncing around, so I've zip tied the replacement to keep it still. Still got to put on a decent main battery connector.
The geared hub motor without a freewheel is a real pain - slowing me down hills. Flat road top speed is 27km/hr (no pedalling), and pedalling above that doesn't help much (no freewheel). Travel time is now 1hr each way, whereas it was 1hr 5mins going in and 1hr 10mins coming home. My effort is a lot less though. I would like to put on a faster motor, with freewheel.
It's an interesting looking rig, and gets heaps of stares!
I wanted a push trailer as it is moveable between bikes and easily disconnectable. Its main purpose is to assist in commuting to work, a 24km trip each way (48km per day).
I got inspiration for my design from the extrawheel, which looks like a great product. http://www.extrawheel.com
First of all, I was dead set on having the attachment point at the rear axle, not the seatpost. Too much force trying to push the bike over when going around a corner under braking or motor power if hooked up at the seatpost. After some stuffing around I decided to use bob trailer skewers - it wasn't worth the hassle making my own. I make my own forks to attach to the skewers though.
Frame of the trailer is made of some scrap angle iron I got from work. Originally I just used the angle section, but it wasn't stiff enough so I had to weld more on and turn most of it to rectangular box section.
For the pivot point I just used the fork and headtube from an old kids bike.
You can see a set of wheel dropouts half way along in the last photo above. I originally had the trailer very short - as per the extrawheel - but I had problems with stability. The trailer would develop uncontrollable wobbles. Changing the frame to box (as mentioned already) greatly helped (increased stiffness), but the problem was still present. I think the problem was due to the pivot point being almost exactly mid way between the trailer and rear bike wheels. Kinda formed a standing wave pattern, that when started, tended to feed itself rather than die down.
I decided to move the trailer wheel back, and as I was going to do that might as well move it far enough to put the battery in front of the wheel, instead of hanging off beside the wheel like originally planned.
Battery box is an ammo tin with some strategically placed foam.
I'm using a Ping 36V 15Ahr battery. I wanted it in a form that is protected from mechanical damage, whilst still easy to carry (charging at work). I spent some time considering and looking at possible cases etc until one day I noticed a 5L green fuel can. I had seen red ones and stuff before, but when I saw the green one I couldn't resist. Green energy!
Foam on the sides and bottom, with a little breathing room above. Sealed back up with hot glue (surprising strong).
It works and looks perfect! 8) 8)
My motor, geared brushless no freewheel, along with some initial problems, is detailed here:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=9891
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14988
Controller is a 350W ecrazyman.
Overall the trailer turned out a lot longer, heavier and more cumbersome than I had originally planned. Despite this it works very well and is easy and stable to ride. Without the pannier it was a little jumpy/skippy on rough roads, and the drive tyre was wearing very quickly. The small amount of extra weight (which I hated having on my back anyway) seems to really keep it on the road and it doesn't skip now unless riding over a really rough section. 26" trailer wheel means it rolls easily and has common spares with the bike.
I've ridden to work about 15 days now - which would be over 700kms. The ping battery has been flawless. I think it is less than half discharged on arrival at work based on charging time. The original charging connector on the battery broke due to bouncing around, so I've zip tied the replacement to keep it still. Still got to put on a decent main battery connector.
The geared hub motor without a freewheel is a real pain - slowing me down hills. Flat road top speed is 27km/hr (no pedalling), and pedalling above that doesn't help much (no freewheel). Travel time is now 1hr each way, whereas it was 1hr 5mins going in and 1hr 10mins coming home. My effort is a lot less though. I would like to put on a faster motor, with freewheel.
It's an interesting looking rig, and gets heaps of stares!
