Scrapyard Mule 2.0

[tjwilson]

Scrapyard Mule

This a continuation of modifications to the build I had in last summer's Build Off. I originally had every intention of posting documentation of how this went along, as it went along, but time got away from me. With all the images I had I figured I'd go ahead and post after the fact. What follows are changes that came in fits and starts after the Build Off ended. 50% more Mule / 20% more scrap, this turned into quite the contraption. Hoping to use what I learned in a future build.

 

[tjwilson]

Adjustable Head Tube Angle

The handling I ended up with originally was a disappointment. The front dropouts gave me some room to experiment but I wanted a way to adjust the head tube angle too.

 

[tjwilson]

Adjustable Head Tube Angle (continued)

The bottom bracket needed to be repositioned also. Distance was a little too close between the seat and crank. Moved the BB 4" forward before adding the head tube adjustment bolt plate.

Modified the front dropouts to allow adjustment up and down the fork legs.

 

[tjwilson]

Testing Head Tube Angle and Trail

I ran a bunch of ride tests changing the head tube angle and trail. Don't understand why but, the ride was most stable with a negative trail. Maybe because of the lower head tube height, close to the height of the front axle?

I tired keeping the head tube at as shallow an angle as possible. These three configurations were all ridable. I liked the look of the first one but the last proved to be most solid and comfortable.

Approx. 42.5° head tube angle, -1.5" trail

Approx. 47° head tube angle, -1.75" trail

Approx. 51° head tube angle, -2.625" trail

 

[tjwilson]

Second Bottom Bracket Position Adjustment

Seemed that the 4 inch stretch forward was a little too much. Also needed more room between the bottom bracket and head tube. Moved the BB down an inch and back an inch.

Before Repositioning

After Repositioning

The original handlebars received a new bend so they'd be reachable with the new head tube angle.

 

[MattiThundrrr]

Industrial art. I don't understand half of what you said, but this i get:

Can't wait to see how it goes

 

[tjwilson]

Seat Adjustment

Some of the designs that I'm using this as a test bed for look better with a seat position a little higher and more forward. This is a seat position adapter made from a handlebar extension.

Tried to keep the distance from the middle of the seat to the crank center the same in the lower and upper seat positions. Missed the mark a little but it's close enough to prove out the ergonomics.

 

[tjwilson]

Front Suspension

Satisfied with the seat / crank / rake / trail, etc. it was time to address the front fork and dropouts. I wanted to add some type of suspension. The design for this came from researching different custom motorcycle designs. The general idea is that a lever that connects the linkage to the front wheel also allows rotation on the steering axis. Easier to understand in pictures than to try to explain.

This is a "tool" I made to locate the attachment point between the frame mounted shock and fork linkage. Basically just tubing that slips into the head tube and bolt that slips into the tubing.

This shows the lever that the "tool" locates and the frame pivot point for the lever.

Lever welded and shock linkage attached.

Pieces and parts for the frame shock and shock mount. The shock is a cut off end from a mountain bike fork.

I bent and trimmed the fork legs.

Overview shots of modified fork legs, shock and lever.

 

[tjwilson]

Connecting the Dots Between the Front Axle and Lever

 

[tjwilson]

Trouble Shooting

The original set-up worked but had issues. When turning, the front wheel would lean toward the opposite side of the turn direction. First thought was that the lever wasn't mounted ridged enough to the frame and was allowing the linkage to shift. Others problems with the lever included too small of a rotation diameter at the steering axis mounting point and an off center position from the steering axis. Time for a new lever and frame mount point.

Here is a before and after looking down the head tube. Locating tool failed the first time but worked pretty good second time around.

Overview showing shock linkage.

 

[tjwilson]

Better But...

Still too much front wheel movement side to side while turning. First modification added pivot levers at the top of the fork legs.

Getting better but still not good enough. Next design tried to strengthen the linkage and provide stronger upper pivot points. Thought I had an overall shot of the finished linkage but I don't. These show how only the linkage sides attached and, overall shots of the finished linkage itself.

 

[tjwilson]

Back to the Drawing Board

This design ended up being the winner. I'm pretty sure any wheel movement at this point can be attributed to play in the linkage attachments. On a less Frankenstein of a build application I'll be able to address that. I ended up strengthening the top linkage by making an "H" shaped lever that securely attaches to the fork legs and frame lever. I also added a second heim joint to smooth out the suspension movement and turning.

Even better alignment to the turning axis too.

 

[hamqqea]

Testing Head Tube Angle and Trail

I ran a bunch of ride tests changing the head tube angle and trail. Don't understand why but, the ride was most stable with a negative trail. Maybe because of the lower head tube height, close to the height of the front axle?

I tired keeping the head tube at as shallow an angle as possible. These three configurations were all ridable. I liked the look of the first one but the last proved to be most solid and comfortable.

Approx. 42.5° head tube angle, -1.5" trail
View attachment 145448

Approx. 47° head tube angle, -1.75" trail
View attachment 145449

Approx. 51° head tube angle, -2.625" trail
View attachment 145450

Thanks for providing data Cool stuff, including the rake adjuster. Perhaps make it quicker to change for looks and parking. Not clear if it's a feature you intend keep.

 

[ifitsfreeitsforme]

wow.

 

[toro1978]

I am immensely impressed with the overingeneered suspension. I also love the headtube adjustment option.
I think the original bike, as it was in the build off (got my vote) had really beautiful straight lines.
The redesigned version is pretty awesome too, from a fabricating point of view, but I liked the previous look better.
But I do realize that rideability is more important unless it is supposed to stay a showpiece only.

 

[Wildcat]

Great build! I looked at it all, but it's like a chemistry class I had a few years ago, I had no idea what was going on, just nodded my approval as the class went on and prayed I didn't get asked any questions.

 

[MattiThundrrr]

I agree with Toro. This thing is incredible. The first version was a beautiful artistic statement, this one is a beautiful engineering statement. I understand both, but the first was speaking my language

 

[tjwilson]

Thanks for providing data Cool stuff, including the rake adjuster. Perhaps make it quicker to change for looks and parking. Not clear if it's a feature you intend keep.

My only thinking with the adjustable rake was to find the best angle for handling. But, that is an interesting thought.

 

[tjwilson]

I am immensely impressed with the overingeneered suspension. I also love the headtube adjustment option.
I think the original bike, as it was in the build off (got my vote) had really beautiful straight lines.
The redesigned version is pretty awesome too, from a fabricating point of view, but I liked the previous look better.
But I do realize that rideability is more important unless it is supposed to stay a showpiece only.

I agree with Toro. This thing is incredible. The first version was a beautiful artistic statement, this one is a beautiful engineering statement. I understand both, but the first was speaking my language

Thank you. I agree regarding the look of the original version. Well, except for those monster front dropouts anyway! From the start I really wanted to use this as a testbed to sort out riding position and suspension ideas I wasn't confident in. I plan to hopefully use the lessons learned in later designs.

This example is still in the rough stage but shows a possible direction. Basically it takes styling ques from a Spaceliner and tries to apply them the Scrapyard Mule stretch cruiser "platform".

 

[MattiThundrrr]

I figured this was a continuation of the first, your design looks like a happy medium between 1 and 2. Awesome process to follow, thanks for bringing us along