Duke University Motorsports is a student group that designs and builds open wheel, single seat race cars to compete in the Formula SAE competition sponsored by the Society of Automotive Engineers. The team consists of Duke students from both Pratt and Trinity, in all classes. The purpose of the team is to provide students with a way to gain practical design and manufacturing experience in a fun and challenging setting.

Friday, October 26, 2012

Machining and Drivetrain Redesign Braindump

Hi there; I am going to do my best to summarize what I have been working on over the summer and this fall; admittedly, I should have made earlier posts, so this is going to be somewhat of a long braindump:

Phase 1: Summer Planning and Drivetrain Redesign Version 1

Over the summer, I put in significant hours (a) learning Computer Aided Machining and (b) redesigning the drivetrain. I am leading both the Drivetrain and WHUBS teams this year, so I needed to put in some serious hours so that I could hit the ground running this fall.

The Drivetrain (and the accompanying rear portion of the frame/suspension) is the part of the car that is undergoing the most changes this year, mostly because it was the most problematic part of the car last year. The main issues that version 1 of my redesign sought to address were:
  1. Last year, we ran too sharp of an angle from the halfshafts to inner tripod housings, so there was significant friction and we actually had the halfshafts pop out of the tripod housings.
  2. Last year, we tried to go to a rigid mounting system (no more turnbuckle) for the bearing carriers, but this had unintended consequences when vibrations created a noticeable side-to-side wobble of the drivetrain when we started turning the chain.
  3. Last year, the bottom of the left and right bearing carriers were mounted at different locations (so they weren't coaxial, so adjustment (which involved the use of shims) would cause misalignment.
  4. There were also some little things within the design (I won't list them all) that I updated/improved to make our CAD model of the drivetrain better.
In order to solve these problems, version 1 of my redesign includes (a) a new turnbuckle system which will solve the vibration and adjustment issues (b) coaxial mounting points for the bearing carriers so that adjustment does not create misalignments and (c) a new mounting location with respect to the frame to cut the halfshaft angle from roughly 10-12 degrees to 5-6 degrees. Below are screen shots of Version 1 of my redesign drivetrain:

Phase 2: Crash Course in Machining

When I arrived at Duke this fall I needed to get practice milling things and using CAM programs to make our parts. I did a little bit last year, but not very much. So, I decided to start small and make all of the small aluminum parts we have on the car, making small improvements/refinements along the way. First I made all 8 of the camber blocks, writing a nice CAM program (including 3D operations which were discovered last year) to make the camber blocks look nicer than last years. Then I made the camber shims, which I decided to redesign so that they are slide-on (making taking them on and off a lot easier) and cutting out excess material (I cut the weight of the camber shims by over 30%); below are pictures of the old and new camber shims. Then I made the ARB support blocks (no change from last year's design) and the front bellcranks (no change from last year's design). I am saving the rear bellcranks for later because Yoshi is going to change them slightly to eliminate current suspension rod interference.

Phase 3: Drivetrain Redesign Version 2 and Machining

I sat down with Dr. Simmons to look at my drivetrain redesign and talk about press fits for bearings (he is teaching me how to dimension things correctly for press fits), and he suggested further redesign, pointing out that the whole o-ring system between the stubshafts and diff caps design that we have been using for years is not a very good design (the o-rings got seriously beat up last year). So, I made Drivetrain Redesign V2 to incorporate a new bearing system that has bearings replacing the o-rings. This involved redesigning the diff caps, stub shafts, and picking out new standard bearings to use. Also, as a little additional features, I decided to add in little guiding extensions on the diff caps that will slide into the diff/rotor so that it is centered better (instead of having the bolts do all of the work). Below are pictures of the of the Drivetrain Redesign V2:

Over Fall Break, I successfully machined the rear sprocket (I am pleased with how it looks), and Dr. Simmons generously took the time to use the CNC lathe in the professional shop to make the general shape of the diff caps (I still need to mill the non-circular stuff and drill holes); the CNC lathe is a much faster and more accurate way to make the diff caps (it would have a long time (at least 5x) to mill the diff caps). I am going to make the bearing carriers this weekend (and maybe finish up the diff caps). Goodfellow is working on the stubshafts. So, considering that we are probably going to reuse Fette's Vette's diff (and I can take the acrylic surround that I made last year, and we can potentially use the brake calipers as well), all that will be left to make to finish the Drivetrain are the brake rotors and tripod housings (which shouldn't be that difficult). I will also have to make the turnbuckles, but that might be something I will wait on to make.

When I am done with the Drivetrain in a couple weeks I will post more actual pictures (instead of just CAD stuff); for now I just have the picture of the rear sprocket I made:

This concludes my brain dump of stuff I have been working on. 

I also want to give a shout-out/thankyou to Dr. Simmons who has been really helpful to me this fall; he has given me valuable design advice and has spent time with us in the garage helping us with whatever we need advice on. 


  1. Hi buddy...
    Thanks for sharing your experience... how u had designed the machine & how u would succeed finally. It is really constructive to us.
    Machining Ultem

  2. Thanks for sharing your valuable design advice with us. Machining and Drivetrain Redesign enhanced the CNC lathe as it is much faster and more accurate way to make the diff caps.
    Machining Ultem