Bobs 2024 Build Off Build

[ezcome-ezgo]

2.75 seems sufficient for a minibike

 

[Master Hack]

I'm lost! Too much science and technical shyt!
I don't unnastan!

 

[bob58o]

This should be close to the actual build.
About 25” from floor to top of “back bone.”

Reminder: Backbone is 1x3x 1/8” x ~35”

 

[ezcome-ezgo]

Looks pretty righteous

 

[Whitetrashrocker]

Looks pretty righteous

That head tube looks pretty righteous also

 

[bob58o]

Now I probably need some magnets and was looking at that this fixture table. It 24x36”
And it is really thin. 4mm top is close to 5/32”

I’m going over different ways to complete the frame besides the ole sawhorse shape.

 

[bob58o]

Maybe a single down tube, single cradle?
Then some gusseting to support the edges of the engine mounting plate?

I think the original idea I had was a double cradle with the engine plate suspended (by weld) to the bottom of the dual cradle rails?

The steel I have for those bottom rails are pretty hefty.
1.5 x 2.5 x 1/8” IIRC

The steel I have and plan on using for down tube(s) and to connect the bottom rails to top backbone is 1” x 1.5” x 1/8”

 

[bob58o]

Then again. Sawhorse…. Because simple and triangles…

 

[ezcome-ezgo]

 

[Master Hack]

The steel I have for those bottom rails are pretty hefty.
1.5 x 2.5 x 1/8” IIRC

Ya think?
Ya building a tank? Yer not going to worry about material failure are ya?

 

[bob58o]

Ya think?
Ya building a tank? Yer not going to worry about material failure are ya?

I figured most minibikes are like 1” round 0.120 wall. Square is less strong, right? So I figured as long as I used 1x1-1/2” or larger… I should be good. Plus I want to make sure it can never be moved down the stairs and outside. It’s gunna have to live in my living room for ever.

 

[bob58o]

View attachment 149559

Too Round! Requires too many slot cuts and welds.

 

[bob58o]

View attachment 149559

I’m worried that those front corner things might dip into the pavement when turning. I’m not really sure how to test that???

Im having a hard time visualizing in my head what happens when leaning and turning.

But if I just think as those corners as really low foot pegs I can visualize it easier.

 

[bob58o]

I suppose splitting the difference would be something like this…

Single down tube… Double cradle?
But pointy instead of bendy?

 

[Master Hack]

I know a guy with a tubing bender.
Go with the single down tube as above.
There is only so much ya can do with sq/rect tubing. Round in mo bedder and mo purdier in some places

 

[bob58o]

I do like the single down tube.
I’m gunna halfta re-measure cause I can’t re-member how tall the engine is with the stoopid charger on top.

I’m sure it’s posted somewhere in this thread but who’s gunna read 30 pages of this crap.

I know I was thinking about the 2-1/2” dimension of those bottom rails when asking how much heigth is needed from engine mount to bottom of backbone.

If I think about it…
1” pillow block bearing puts the center of the axle 36.5mm (~ 1.5”) below the bottom of the bottom rail. And 13” rear tire has 6.5” radius.

So the bottom of the bottom rail sits 8” off the ground. The top of bottom rail would sit 10.5” off the ground.

The top of backbone sits 25” off the ground
The bottom of the back one sits 22” off the ground.

Hmmm, only 14” from bottom of bottom to bottom of top???? That doesn’t seem right??

I’m fairly certain I thought about this in advance…

 

[bob58o]

Here we go…
The height of engine plus blower is exactly equal to one chair.

So when it comes to the engine mounting plate… I only see it working with the plate mounted to the bottom of the bottom with the engine sitting between the bottom rails (as opposed to mounting the plate to the top of the rails).

 

[bob58o]

 

[Master Hack]

Maybe put the engine on a .187 or .250 plate of the appropriate size, attach it at the rear at the desired height put a flange on the front to attach the down tube to?
that would eliminate the triangle thingy in front and keep the hardware hidden underneath.

 

[bob58o]

Maybe put the engine on a .187 or .250 plate of the appropriate size, attach it at the rear at the desired height put a flange on the front to attach the down tube to?
that would eliminate the triangle thingy in front and keep the hardware hidden underneath.

So some sort of box thing in the rear (green line and back). Then just plate? With rear of plate welded to the box? And front of plate attached to a single down tube in some fashion?

In comparison to the photo below, there wouldn’t be any tubing along side or under the plate, but perhaps some sort of cross member behind that the plate could attach to.