Woo Hoo!!

All that component work is gonna pay off soon with an assembled cart.

I ordered the parts for the dynomometer today -- that will be the next project after assembly of the vehicle. The 6.5HP Honda engine will spin the wheels and allow us to test initial mechanical reliablility and also prop behavior at static thrust. Data from the sensors will tell us if at windspeed the vehicle will accelerate or fall back ... a rather important distinction. :-)

Final load cells integrated.

Finished up the outboard bulkhead bearing points -- installed the load-cell brackets (lower right of shiny bearing bracket and also installed the limiting stops on each side.


I'm not going to install the brake caliper brackets until after dyno testing (no need for brakes on the dyno), but other than that this rear assembly is ready to install on the chassis.

Next up -- have to build the cap for the prop stand pylons then mount the prop shaft bearings, brake rotor and rear sprocket before mounting the cap and preparing to mount the prop on the chassis.

To the back of the bus

Worked on the mounting and assembly of the lower rear of the vehicle this weekend.

Here I'm installing the mid bearing bulkheads:



Bulkheads and bearings in place, along with the brake rotors, ratchet hubs and sprocket cassette.



A shot of the (near) total rear assembly.




A closer look at the 'half-shaft' with the ratchet hub installed and the linear bearing bracket where the drive axle load cell will be installed. I'll get the load cells in there tomorrow evening.

Once the vehicle gets off the dyno, these 'half-shafts' will be replaced with full shafts to widen the vehicle track by about 4ft for more stability in the wind.

No clearance Clarence

Blades on the hub and balanced. Wish we had room to spin it up -- we're about to pull the chassis back in the shop and start nailing stuff to it. This weekend we'll start that process.

One DDWFTTW vehicle to go please.

It appears we should have ordered our DDWFTTW cart from an online Chinese hobby shop -- our buddy Tim built an entire airplane this evening in the time it took us to install just one prop hub collar.



*$!$% you Tim.

Blow me away

Rick just sent me a shot of the pressure transducers we'll be using for our pitot tubes, and a couple more shots of the telemetry board in process.

The calm before the storm.

This evening we will final assemble the prop hub (sans telemetry), install the blades and balance them.

A final shot of the parts and sub-assemblies of the instrumented hub.

Bones on a stick

Our propeller spar is a tapered carbon shaft. Our dogbone bearings and collar sets are all the same size. We built up 'pads' in the appropriate locations at the spar roots to allow the hub to interface tightly with the spars.

Since our spars were a bit longer than we needed for our 16' propeller, we added an extra set of pads outboard from the design point. By shifting the pads used and thus changing the diameter of the propeller by about 15% we can change the effective twist of the prop from it's design point.

Options are good and we'll test in both locations to see where we get the best results. If the original location is the best, we'll chop that last pad and its 6" of the spar off and discard.

Tiny brains

While I've been turning billet into shavings (and other assorted goodies), Rick has been busy with the instrumentation.

We got our custom PC boards in that our buddy Christian Klippel designed for us (Thanks a bunch Christian) and soon after our components also arrived. Rick went to work under the glass with the surface mount components, tweezers and the soldering iron.

What's your angle?

The last mechanical piece of the propeller hub left to fabricate was the pitch adjusters. These are only adjustable between runs currently, but are positioned such that if we later decide to add run-adjustable pitch we can do so.

Hex me

A few weeks ago I made the 'ratchet hubs' that went between the wheels/prop and the transmission. The hubs themselves fit nicely on our aluminum axles (as they were designed to do), but I had to come up with some way to connect the half shafts into the ratchet hub. Tums out that 3/4" hex bar slides nicely into the axles.

I drilled out the hex for weight savings. Also on the prop shaft we may eventually run a control rod through the hollow shaft for variable pitch control. If I didn't also drill the hex out I would be unable to run this control rod through the assembly.


As previously mentioned, my hex bar was 3/4", but my ratchet takes an 11/16" hex head so again a bit of milling to make them match up.

All that is left to do is secure the hex stub inside the shaft on the right. Perhaps a roll pin or two. I'll work on that tomorrow evening.

Odds and ends

A bit of pickup work this evening -- odds and ends that will allow the final assembly of the prop hub and the installation of the prop spars:

I milled off the tops of the stop and load cell contact bolts. The hub can now freely move fore and aft on the roller even under load. Also adjusted all the stops.



I installed the three load cell over-load limit set screws in the thrust plate. These insure we don't deform the load cells

I drilled, tapped and installed the screws in the prop spar 'dog bones' that hold the bearings in place. These bearings are inset into the bones and generally will be pulled into their sockets -- the screws only hold the bearings in place when not under load.

I also sliced the small bronze sleeves that will act as spacers -- holding the spar collars against the bearings but away from the bones. This will allow the spar to rotate freely for pitch adjustment.

Oh for a CNC mill

The last major part to the prop hub was the torque paddle. I cranked that out last night.

On each end of the paddle is a roller assembly that will allow the prop hub to compress the thrust load cells without binding up on the torque arms.

The assembled paddle.

The paddle installed.

Getting closer.

A shot of the thrust plate with the three load cells mounted radially. There is a thrust bearing which will press against these cells.


The thrust and torque cells installed. There is major piece missing on the rear of the assembly -- the 'paddle' which transfers torque from the axle to the hub through those two load cells. That component is my next milling project ... this evening.

Where it all comes together

First assembly of most of the basic hub components including the thrust plate shown in the last picture. The load cell brackets and stops can be seen on the rear place (which is facing outward in the first two pics).

Throw me a freakin' bone here

Drilling and tapping the central spar 'dog bones'