Axle broke traveling 30mph.

[bike4life]

I am lazy and the moving the frame inward wont really work that well. Do you think 1" mild steel rod will do the trick at a distance of 12" span or should i go thicker.... THX

Ok fine, I will go 1.5” cold rolled steel rod. I think that should work fantastic across the 12” span. According to a calculator tool and machinery’s handbook, the 1.5” rod has an area moment of inertia of .25 while the 5/8 rod has one of 0.007. The formula for beam deflection is proportional to length cubed, so if I modified the frame to 6” axle, I would get 1/8 the deflection. But by upgrading to 1.5”, I get around 1/30 the deflection. Compared to a 1” axle, with an inertial area of 0.05, it’s 1/5 the deflection at the center. Not sure if these formulas don’t work that well for axles, but still.....

 

[Wrench]

I'm sure you know why your axle broke. Your axle is too long and the frame flexes
The Frame needs to be as close to the wheel bearings as possible with a small spacers.
I see your Wheel is fixed to the axle and spins on the pillow block bearings. - Bad design
I really think ya need to redesign and improve the frame where and how the wheel mounts.
I know your first attempt was just a Prototype.
Your on to something COOL. Are ya gonna paint it white and start selling Ice Cream? LOL

Mount your wheel the same way a motorcycle wheel is mounted.
Nut - washer - Frame - Spacer - Bearing - Spacer - Bearing - Spacer - Frame - washer - Hex Head of Axle

 

[Karl Snarl]

If you look at the pictures you can see that it failed really close to the wheel. It also spans about a 12" distance and i know that the deflection of static beams drop off when they span long, by a factor of x^3 but not sure how that relates to dynamic/spinning axles. Maybe the weld weakened the metal or perhaps just simple beams laws say the highest stress on a beam is dead center, and that was the closest point to the center it could fail. In fact, about 1/2" above the weld.... It was cold rolled steel. A day before the axle broke i did notice it was slightly bent inwards, due to the large forces on the wheel.

I think an upgrade to 1" mild steel is a good idea. I was gonna use cold rolled but its not in stock, and i think 1" should be pretty dam strong. I cant see that failing. Plus i am gonna weld gusset plates around the axle to the wheel hub to increase its diameter and toughness. I dont understand how you can buy grade 5 or 8 rod stock, i thought only bolts. This axle below is huge, crazy for that thing to break...

you can buy rod in any grade you want. cold rolled, forged, pot metal, graded metal, structural a325 etc etc. i work with metal all day long. im a fabricator. so many grades of metal rod, you wouldn't belive it if i listed them all. i won't, cause really tht would take a while. lol

 

[inspectorcritic]

Looks like a miserable piece of s**t check Good Will stores other thrift shops for baby bike trailers or fly a sign for a few days get a hundred bucks order a twin stroller from either Targets or Walmart don't go to REI or any bike shops they soak those mommys for $300.00 to $400.00 kid has to go without Gerber slop and clean disposable diapers, good luck.

 

[CrazyDan]

I actually agree with inspector on this one. A good used baby (or dog) trailer would make a great pusher, some even come with brakes.

 

[Karl Snarl]

Looks like a miserable piece of sh*t check Good Will stores other thrift shops for baby bike trailers or fly a sign for a few days get a hundred bucks order a twin stroller from either Targets or Walmart don't go to REI or any bike shops they soak those mommys for $300.00 to $400.00 kid has to go without Gerber slop and clean disposable diapers, good luck.

he's a kid, still learning. give the poor guy a break, no pun intended. he's gotta eat some gravel before he realizes lime rock doesn't build strong bones. i know i've had my fair share. lol

 

[bike4life]

Looks like a miserable piece of sh*t check Good Will stores other thrift shops for baby bike trailers or fly a sign for a few days get a hundred bucks order a twin stroller from either Targets or Walmart don't go to REI or any bike shops they soak those mommys for $300.00 to $400.00 kid has to go without Gerber slop and clean disposable diapers, good luck.

Inspector and the rest. Didn't realize how slanted your perspectives are and you should really learn about constructive criticism.
On a real note, A) the frame is exponentially stronger and better and B) beauty is in the eye of the beholder.

Angle Iron and such have a higher Moment of Inertia than any trailer to hand the stresses, its overbuilt. Before you speak, know what your talking about. Realize that most of these strollers and such are thin walled tubing, not ideal. I guarantee that the frame will never fail, once the axle is upgraded to 1.5", it will have 30x the moment of inertia and 1/30th the deflection. (Formula for rod is proportional to radius^4). also, braking distance follows momentum conservation. You should really worry about speeds and not mass for your bikes. When you go from 15mph to 45mph, your braking distance increases by 9 times. So a 15mph bike carrying 1/2 a ton will have the same braking distance as one of you guys doing 45.

I weigh 120, trailer 80, bike 20lbs for a total of 220lbs. It has the same braking distance as a 200lb guy and his 2 stroke bike if the speeds are the same. The trailer is fine as long as i dont gain weight (which i wont).

Not that your opinion matters. But I will say, from the build, I learned a lot about fabrication and other stuff, and sometimes the journey is more important than the destination. Perhaps, I can use this as a stepping stone to move on to new projects.
I got better stuff to do right now than argue.
Also, lime rock can build strong bones if you separate the Calcium from the Carbonate and then eat the calcium.
Best wishes.

 

[CrazyDan]

There was a guy in my town that made a pusher with the back half of a 50cc pit bike. It worked well in straight lines on the flats, but he said it wanted to jackknife on turns, and downhill if he forgot to get off the throttle before hitting the brakes. I haven't seen him riding it in years now, he's moved to mid-drive since.
What you do is you. I'm not hating, just feel you designed the trailer a bit wide for a single wheel pusher. I think you should have replicated a current trailer that has great reviews on turns and high speed straights, since you wanted to build it yourself. I just hope you don't hurt yourself on your endeavor of attempting to re-invent the motorcycle using ideas that have been tried and canned for a reason.

 

[bike4life]

There was a guy in my town that made a pusher with the back half of a 50cc pit bike. It worked well in straight lines on the flats, but he said it wanted to jackknife on turns, and downhill if he forgot to get off the throttle before hitting the brakes. I haven't seen him riding it in years now, he's moved to mid-drive since.
What you do is you. I'm not hating, just feel you designed the trailer a bit wide for a single wheel pusher. I think you should have replicated a current trailer that has great reviews on turns and high speed straights, since you wanted to build it yourself. I just hope you don't hurt yourself on your endeavor of attempting to re-invent the motorcycle using ideas that have been tried and canned for a reason.

Yeah. I feel you. Looks like we understand each other now. I thought most of this was personal. What your saying sounds reasonable. Thx for your concern. However, I do plan on moving in the axle and pillow blocks to limit the distance, and also upgrading the axle size, following reccomendations and also over building it a little. I know there are flaws in the design, and it would be much easier and safer to build a rear drive. The next bike i build, will be a rear drive, and then this one would be retired for a while.

I agree that theres a good reason why pusher bikes arent commerically made. But i also know that personally, for me jacknifing is not a problem with my design. At first it was, but i made a few corrections and its now perfect. Obviously, my axle broke in half traveling 30 and i didnt flip over, so i think my design passes.

 

[CrazyDan]

I like to take twisties hard, I hit the apex and roll on the throttle hard right after. I know it's something you can't do, and I would be bored if I couldn't lol. I'm biased because I know how much more fun it is to run it like current motorcycles. There is a reason mid engine rear wheel drive is the sole survivor in the motorcycle scene since it's inception. What you are doing right now is working through ideas the original motorcycle builders had, and discarded after some r&d. You will be flabbergasted riding a mid engine/rear drive after this pusher if you never rode a dirtbike. If you've rode a dirtbike, you should be disappointed with the trailer.