Last week we chose the tubes which will be the main building blocks for the frame.
I looked into sizes and found additional, interesting model - 12mm ID and 16mm OD.
This one is more common then the 18mm tube and with better pricing.
So the table is slightly updated:
And the factor of safety is still OK, around 4.
We can go higher but adding weight is less desired.
Now let's go to the hardware design.
The tubes are ordered, meanwhile I can get the end-units ready.
The obvious choice is to 3d-print them. The challenge here is the printing material. It is PLA which is very weak compared to carbon or aluminum.
The challenge is to design the units so they will hold together with the frame. Luckily, we already have these loads.
The bending moments are lower towards the ends of the frame.
If there is a way to not stress the unit, we'll get what we want.
This is what I came up with:
The carbon tubes run through the entire length of the end units, the central tube is longer.
The trucks are standard with standard interface.
So, what is the idea here?
When the frame bends, the end units will rotate around the wheels. No relative deformation in the end units, so no stresses.
We'll see how it holds up in the future. But so far I'm happy with this design.
Here is a nice time lapse of the print itself:
Will PLA hold?