07/03/03 Some steady progress. Had a meeting with the principals of Davis Tool, a large machine shop locally. They certainly have the capabilities to do all the necessary work (even to assemble limited production when/if it comes to that). Hopefully the pricing will be something I can work with. During the tour of the facility saw their Thunder Mustang project - an awesome machine! They even have another kit sitting in the back waiting for a buyer. It seems aviation is going to draw me back in one of these days.... But I digress. In the meantime, with luck I may have found the vendor I need.
Also got word (and even pictures) on the diffs. The front and rear are complete and on the way to me, to arrive in a couple of days. The center box is still awaiting custom gearing from Quaife.
Also made more progress on the design itself. Made improvements to the front venturi exhaust ducts...
Then started in on the suspension and chassis. I've decided to replace balljoints with rodends for strength reasons. This is where some of the benefits of extra-long suspension arms become apparent. With maximum +/- 2" of travel the suspension arm angle only changes +/- 4 degrees. That results in maximum misalignment of only 8 degrees for the top joint - which is good because it's only rated to 9 degrees. My actual anticipated travel is closer to +/- 1" (the Stohr car supposedly only uses 0.25" of travel) so there should be plenty of margin. I might even limit suspension travel to +/- 1.5" just to be on the safe side.
In the above picture you can also see how steering angle is limited by the CV joint to about 20 degrees. Not a big deal due to the very short wheelbase - but if I end up needing more angle I can always use a standard VW outboard joint. It should plug right in to the hub carrier and the halfshaft. Good to know I have options.
07/08/03 As often happens, an e-mail comment set me on another course (thanks, Marcel!). The basic reasoning being that I should really take into account the rollcage and engine/fuel mounting points in the chassis design, and not focus solely on the backbone. True enough, a quick run of my in-head 3D simulator (don't ask ;) proved that indeed the backbone will be all but redundant once the rest is added, and will need to look very differently to ensure lightest/stiffest overal design. But before I can design the rollcage I needed to create a simple model of the driver. Some quick measurements (at 5'11" and 180 lbs I'm fairly average build) and a rough model was created - not to Hollywood standards but good enough for my purposes.
The parametric nature of the model enables me to check things like foot pedal motion range:
With the driver in it, the car finally takes on some scale. It is a tiny thing, except in width...
Also taking advantage of the parametrics I created a 'bystander' to give a further idea of the car's diminutive size. Somehow the scene looks like something out of a sci-fi movie :)
07/09/03 Just couldn't resist playing with some rendering options in SolidWorks. What can I say.
07/21/03 Been working on the design a lot - pretty much full time. It is amazing how much work this is. Progress may seem slow, but it is steady. The design is packaged pretty tightly so every change has a lot of consequences. Redid the suspension pickups again - they are now sheetmetal brackets, which my vendor can do a lot easier. They can laser-cut all the brackets for the chassis in one shot and then CNC bend them before welding. Also happens to save 6 lbs this way.
The main 'backbone' tubes, in addition to locating the suspension pickups, also serve as chain guards. I finally have a design where I'm comfortable with the chain under the driver's elbow, for if a chain were to break now it will have a 1" chromoly steel tube to get through before it gets to me. There will be thin nylon friction surfaces installed between the chain and the tubes to control chain whip and limit wear on all parts. Also got the Wilwood pedal assembly and master cylinders into CAD. Positioning these parts of course required tweaking the bodywork, which also had to be adjusted for the revisions to the underbody tunnels that resulted from the chassis changes so far...
With the rollcage defined around the driver (and clearanced to the bodywork), the chassis development can now move forward again. It's an iterative process.
While I'm working on all that, Davis Tool is working up some quotes based on preliminary data. They are also machining the sprockets (which had the wrong hole size) and will anodize them too. The sprockets were originally supposed to center on the six studs that secure them to the diffs, but fortunately I had the foresight of having a pilot bore machined onto the diff flanges - centering on the studs would result in too much runout. This is because the studs are not very straight due to them being very close to the edge of the flanges. So now I'm just having a pilot bore cut into the sprockets and they'll center on that, with the studs only transmitting torque. Kind of like the modern hub-centric wheels. Eliminating runout is critical in this application as I intend to run virtually no slack in the chains. And so it goes... Clearly there is almost no chance of getting it driveable this summer.
One of the benefits of sharing the development of the dp1 on the web is that effectively I get world-wide peer review - something very valuable when working solo and not as part of a team. As an example, just a few hours after I posted the above I got this particularly well-presented suggestion from Steve Worden in California:
He makes some very good points and while I can only use this in six locations out of eight (the other two would interfere with the chains), I may do some variation on the theme. Many thanks to Steve and others who have taken the time to review and critique my design. It definitely helps.