I am currently working on a small project on my 3T VOLA aero-bar to get a BTA aero-bottle bridge replacement to the stock bridge provided by 3T.

I have always wanted to install an aero bottle (like the profile design HC bottle) or at least a standard bottle cage with a standard bottle in between the arms.
There is always the solution to install some brackets between the extension but with the 3T VOLA aero bar, I have always found that the bottle was too much Forward and that the structural link between the block/raisers ( which I call the bridge) was taking useful space.

Note that 3T does not allow to modify their products and doing so would void any warranty.

Here are the few steps for my project:

1. Design a bridge that would re-use existing provisions on the 3T VOLA aero-bar.

I came up with few different designs allowing to have the bottle cage installed on the bridge at few different locations (forward & aft).
The bridge holes are exactly at the same locations than the 3T bridge.
I have done few designs where the bottle z-location (height) could vary (see pictures) but for aerodynamic & cost purposes I will keep the bottle at the same height as the arm. (i.e. the final bridge most likely going to be a plate: V1 on the picture below).


2. Prototyping check

I have used a 3D printer to prototype the V2 model (see picture). The 3D printed part is a plastic part ( ABS plastic) which is not structural. Tensile strength is around 31MPa, structural Aluminum like 2024 T3 have tensile strength in the range of 400MPa and carbon UD in the range of 600MPa in the fiber direction.

I have then installed the prototype on the bike to verify fit and function. As you can see on the picture the fit is perfect.
I have had no time to model in 3D the rest of the bar and the bottle/bottle cage but I am going to do so in the coming weeks.

3. Short term solution

In the short term solution, I am going to use both the 3D printed bracket and the 3T bridge. I will installed the 3T bridge upside down. I just want to make sure the stock screws have enough thread engagement after stacking up the two bridge. If not I will get new screws. A good rule is to make sure you have at least 2D of thread engagement.

4. Long term solution

For the long term solution, I will be working to make the bridge structural, likely by using 2024 T3. The thickness of the plate will be chosen so that it can withstand pre-determined loads. I am currently in the process of defining the load cases. I will also most likely model the 3T bridge and do a side by side comparison of inertia/stiffness and strength (all that using finite element analysis). My bridge is inherently larger than the 3T bridge but at the moment I don’t think I want to have it with the raise portion (as the 3T one).

At the moment I am thinking the that the bridge is mainly taking load in its plane and that compression failure or buckling are to be checked.
To give you an order of magnitude using the design V4 a compression load of 100N in the direction of the bridge, it would take a load 58 times greater to get the first buckling mode. Meaning 100N x 58 =5800N = 591 Kg. I do not think anybody can put such load into the bridge. Stress in the bracket are not an issue with the 100N.

I am thinking that the shape of the 3T bridge is going to be more compliant than my bridge. I think the 3T bridge does have some built in in-plane springiness which probably enhance helps damping out some vibration.

Finally, I will need to ride the bike to make sure there is no rattling or odd vibration. If there is I might have to center the bottle more on the bridge or design slightly different platform.

I would be glad to hear what comments you have on this small project.