What's That Smell?

I didn't do it!

I didn't do it!

My wife has asked me that questions many times. Usually I can just blame it on the dog, but when it's a plastic smell that doesn't work. I've been experimenting with thermoforming Polyethylene terephthalate (PETG) to create a clear lens for the tail lights. This involves placing the material in a metal frame, heating it in the oven until it sags and then quickly draping it over a male mold while hoping that the kitchen police don't arrive until the smell completely dissipates. Last time was a close call and I mumbled my best "I-don't-know" combined with a shrug... I don't think that will work again.

The best way to good results without winding up in the dog house is to use a vacuum forming machine. It's not too hard to build one, but I don't need another project. I had been eyeing one from Centroform, but I didn't want to spend $1,495 on an experiment. After spending some time searching eBay, Craig's List, etc., I found one in a local online equipment auction... and I won it for $193!

It has a built in 1,500 watt heater and two vacuum ports. One is for a shop vac and the other for a vacuum pump. A shop vac will remove a lot of air quickly, but it doesn't have the torque to create a strong vacuum to pull the plastic tightly against the mold. A vacuum pump moves less air, but it has the torque to create a strong vacuum. To put this in perspective here are some typical vacuum inHg (that's inches of mercury) for typical vacuum sources:

  • Single-stage vacuum cleaner: 3.7-4.0
  • Two-stage vacuum cleaner: 5.8-6.6
  • Mouth suction: 15
  • Vacuum pump: 27+

So the manly 5HP super vac moves a lot of air, but can only create a fraction of the vacuum of a diminutive vacuum pump. The Centraform machine has a pressure sensitive valve that automatically closes when the shop vac is no longer able to suction thus enabling the vacuum pump to evacuate what's left.

You might be wondering if the vacuum helps... well it does. If you were at sea level and could weigh a column of air that was one inch square, you would get something in the neighborhood of 14.7 pounds assuming you didn't have a high or low pressure weather system above you at the time. This is called atmospheric pressure and since we're born into it, we take it for granted. However, if I could create a perfect vacuum inside the mold (which I can't), the atmosphere would apply 14.7 psi to the entire mold. So the vacuum essentially results in an evenly distributed, perfectly shaped clamp which is exactly what we want when were forming a hot piece of plastic over a mold.

Male molds are simpler to work with when vacuum formingso one was 3D printed in ABS (that sounds right -- the male mold from Mars is simple whereas a female mold from Venus would require a myriad of strategically placed, and meticulously drilled vacuum holes to create the proper shape without marring the clear surface, an almost impossible task... but I digress). It was trivial to design because the profile of the bezel was already in CAD, so the profile was simply enlarged via an offset operation and then extruded to the desired depth. Since plastic shrinks as it cools during the part will adheres to the mold surface. To solve this the sides of the mold are tapered (referred to as mold draft). On a male mold, the minimum draft angle is 4 degrees. Fortunately SolidWorks has a draft feature built it.

Here's the specifics of first attempt:

Lens Material:

0.1" PETG (aka PET, PETE, PETG)

Mold:

  • Material: 3D print; red ABS with 6% infill
  • 0.1" offset
  • 0.1" chamfer on top edges
  • 0.1" chamfer on corner edges
  • 2.0" deep

I'm really happy with how well the shape and edges came out. However, every defect in the mold was perfectly transferred to lens. In particular you can see a pattern of triangular indents. We were in a hurry when we printed the mold so we set the slicer to a very sparse infill (it feels lighter than balsa wood) and we assume a combination of heat and pressure caused the triangular support structure to print through the top and sides. The mold was also very difficult to remove despite the 5-degree draft. We assume that the mold deformation was a contributing factor.

All in all a successful first test. With a few takeaways:

  • It does work as well as the YouTube videos (at least for 0.1" PETG)
  • Mold must be made stronger
  • Mold must be perfectly smooth
  • 0.1" chamfers worked well for 0.1" PETG

Next step is to buy some thicker PETG as well as research what other types of plastic might work well. I am also going to coat the mold with Evercoat polyester glazing putty, wet sand it and see how it holds up to vacuum forming.

First 3D Print of Tail Light Bezel

This is the first 3D print of the bezel that wraps the OEM bezel that I cut and filed down. The printer needs to be tweaked and we ran out of black filament, so the finish isn't great. However, it's good for the first attempt.

Some observations:

  • The triangular recess in the bottom right was added to provide a rectangular shape with a flat bottom. It will be filled with a piece of red reflector cut via laser.
  • The bottom middle is a little too wide. I'm thinking about thinning the top of the reflector triangle and perhaps creating a recess beyond the tip of the reflector.
  • I haven’t found the courage yet to cut the curve out of the left side of the OEM bezel yet, but that needs to happen. When that's done  the bottom left of the printed bezel will be vertical/straight with no curve. Before I do that, I want to be pretty sure that a 3D-printed bezel will likely work.

First 3D Print and Bezel

I need to design some parts to be 3D printed or CNC machined. I have no CAD skills and although I bought a 3D printer, a MakerBot 2x, a couple of years ago, I never fired it up. So it makes sense to do something simple first...

The removable side-impact bars utilize interlocking couplers. When they're removed the exposed couplers don't look good, so I'm going to make an end cap. I spent an entire day designing the part below. That includes sorting out the printer, installing and learning the CAD software basics and printing the part out. While one day seems like a long time for a simple part like the one the right, it would have been much longer without YouTube! Now that I know the dimensions of the part and the basics I can redraw the part in a few minutes.

I chose Autodesk 123D because it's free, it's approachable by beginners and it has pretty good reviews. In terms of researching packages I found this decision graph and this summary list very useful.

After designing the part, I decided that I wanted to go back and change the fillet on an edge... well the only way to do that is by clicking undo until you get to that step (assuming that the steps are still in the buffer) and then manually redoing all of the subsequent steps. The reason for this is that it's using a 'direct modeling' approach. When you make a change to a solid, such as cutting off a piece or applying a fillet, it's gone. There is no way to get it back other than undo. Parametric-based CAD stores all of the steps and you can go back to any step, change it, and then have that change automatically rippled forward. These packages are usually more expensive and more complicated to use, but that's the direction I'm going. I'm thinking about SolidWorks which is both expensive and overkill for what I'm doing.

I did a test print using the 3D slicer that came with the MakerBot. I would show you a picture of it but my wife threw it out thinking it was some 'Lego junk' -- apparently my kids shouldn't leave their Lego stuff anywhere near the kitchen. In any event, I wasn't crazy about the quality of the print so I bought and installed Simplify3D, a pro-level slicer (please don't tell Esmeralda that because I'd like to bank that mistake -- I'll need it for something I'm sure). However, I couldn't get it to communicate to the printer via USB and the SD card on the printer wasn't working. Frustrated, I searched for a local 3D print shop. I found 3D Hubs which enables you to upload a design and get instantaneous printing quotes from nearby shops. I picked Charles River Maker which is all of 3.4 miles away and had my part printed (they use Simplify3D as well). In the picture below you can see the white, 3D-printed part on the top coupler compared to the bottom coupler which doesn't have the part.

Jeremy was very helpful and he has a bunch of 3D printers (one large enough to print at least a prototype of my tail light bezel) as well as a laser cutter and other cool equipment.

Bezel

I spent several more hours cutting and filing the bezels and almost all of the extraneous pieces have been removed. The picture below is a scan of the passenger side bezel.

There are three primary issues that I'd like to deal with:

  • The right side of the bezel is on a 45-degree angle which hides part of the light and will look weird on a flat-tail car like the SL-C.
  • The right side of the bezel is curved on the top and bottom. The curve on the top should look good because the tail already has a similar curve there, but the bottom curve would look much better if it were straight.
  • The left side of the light is an inch and half or so shorter than the right side. It would look much better if they were the same height (i.e., the top and bottom were parallel).

I think that I can solve all of this by cutting the right side of the bezel off and 3D printing a bezel that surrounds the entire outside edge of the existing bezel (reproducing the interior bezel would be a massive amount of work) and extending the exiting bezel it in the desired places. 

I'm not sure how to import an image into a CAD package yet, so I just did the above in a paint program. It outlines the general direction that I'm thinking:

  • Blue Lines: ~7mm thick border
  • Red Line:  ~3.5mm thick border
  • Green Line: sits on lens and slopes back at what looks 45 degrees per existing piece
  • Yellow Triangle: fill between the blue lines at top surface
  • Orange Triangle: 8mm recess to glue custom-cut reflector on

Tail Lights

I don't like the round tail lights that come with the kit. I really like the newer Lamborghini lights, but they're $4.6k a pair. Which, of course, is just the starting point; before you get into electrical, body work, custom bezels and any mistakes. After looking at countless images online and looking at every car on the road, I decided on aftermarket lights from Buddy Club that were designed for a Toyota FT86, Scion FRS, and Subaru BRZ. They have Lambo-like sequential LEDs, they are relatively flat (a big requirement for the SL-C) and most importantly they are Department of Transportation (DOT) certified. This video shows you what they look like in action.

So I ordered a pair. They look well made, but I sure as hell wish they didn't have "Buddy Club" on the clear lens. I should be able to carefully file and polish that out right? Well no, the letters are on the inside of the lens.

Using a 12v power supply, Will and I were able to quickly determine the basic wiring:

Black: Ground
Black with White Stripe: Brake
Red: Running
White: Turn

The back has four M4 mounting bolts.

In the picture below paper templates have been taped on to show the rear vents, the license plate and the general outline of the "Lambo" tail lights.

The curved bottom section doesn't go with the shape of the tail and it will need to be removed. Fortunately that section is just a non-functional reflector. It looks like the lights could be made to work, but it's going to take a lot of body work, custom brackets, custom flanges, custom clear covers and modifications to the light's housing. Fortunately no changes will made to the LEDs themselves.

So, decision point. Do I a cut up a $550 set of lights and put a hole in the tail section? Hell YES these things are cool!

The clear plastic lens has been cut off with a Dremel abrasive cutoff wheel... made a real mess.

The three screws that hold the rear cover have been removed, the flash mode switch has been cut out and several flanges have been removed. With respect to the switch, open circuit is flutter mode and closed circuit is normal blink mode.

Four screws have been removed to separate the bezel from the LED panel and electronics.

The passive reflector has been removed and the housing was trimmed so that the bottom curved portion can be hidden behind the fiberglass body.

It was really worried about how I was going to blend the light into the tail because the clear lens sloped about 1" from left to right which wasn't going to look right for a flat tail. Other than a 1/4" raised portion of the bezel, which could be ground down, patched and painted, the bezel is flat. Of course I now need to figure out how to make a lens!

The Engine's Where?

You don't have to be a mechanic to realize that something's not right with this picture. The pipe coming out of the engine that is within a 1/4" of an inch of t-boning the chassis is the outlet for the water pump. It's a LS7-based engine and like most engines it expects to be in the front of the car with the radiator directly in front of it. In the case of a mid-engine car, the driver sits between the engine and radiator.

There isn't much room and many builders just notch the pipe and weld it into a into a sharp 90-degree angle. Beyond not looking nice, this approach can lead to cooling problems because there will no doubt be turbulence and turbulence creates air bubbles. Consider that 2% air in the system results in 8% less heat transfer, but 4% air results in a whopping 38% less! 

Fortunately the existing tube is press fitted into the water pump and not hard to remove. After much research I just did what my friend Will did. I had John at Design Enterprises build me a custom part. He machined one end of a stainless steel 90-degree elbow so that it can be press fitted into the water pump. He then machined an adapter from a solid block of stainless steel and TIG welded it to the other end. The adapter serves two purposes: it provides a pronounced bead so that the silicone coolant tube won't slip off and it smoothly transitions from the pump's 1.25" diameter to stainless cooling tube's 1.5" diameter.

This is what the part looked like when I recieved it. 

Some of the weld created a ridge on the inside edge which I filed smooth to reduce turbulence. I also decided to sand the raw tube with 220 and a refinishing pad to give a satin patina and use polishing compound to remove the heat marks from weld. This is what it looks like now. It's ready to install, but I'll have to pull the engine to do that.

To put even a simple thing like this in perspective, I spent a little time here and there over a couple of months thinking about what I might do. I then ordered the part which took about a month to get at which point I spent several hours cleaning it up... and it's still not installed yet!

Pedals

72-603_front_wide1-500x500.jpg

The kit came with a beautiful set of Tilton 72-603 pedals. As you'd expect from a premium racing pedal assembly they are well engineered and massively configurable. The latter being a bit of an issue as the instructions merely state that "pedal position is highly dependent on the driver's preference" and you're looking at bunch of parts on the bench.

The first step is to mount the pedals. The brake pedal is wider than the gas and clutch pedals -- makes sense as the most important thing in any car is stopping. Each pedal can be installed in one of two orientations that provide different mechanical ratios. I wasn't sure which I would prefer so I just picked one. In addition each pedal can be installed in one of two bolt positions which will change the height by 1/2". Since I have small feet, I chose the shorter option -- don't go there, small feet means small shoes and that the body can expend resources growing other appendages. In any event all of these settings will be easy to change even when the pedals are mounted in the car.

The next step was to determine how the pedals should be positioned. With a 1,000 HP motor in a very light car you want the throttle pedal throw to be as long as possible, so I adjusted the min and max limits accordingly.

Next I installed the clutch, front brake and rear brake master cylinders. I upgraded the Wilwood master cylinders to Tiltons because I believe the Tiltons are superior and they use a -4 AN fitting for the reservoir feed rather that a rubber hose and barb, and they have an additional -3 AN fitting on the pressure side which will allow me to cleanly install pressure sensors. Interestingly the front break master cylinder is ¾” and the rear is 7/8". Why? Well during braking a car's momentum shifts forward so more braking is done by the front brakes. So shouldn't the front master cylinder be bigger? Nope, for the same amount of pedal travel the smaller cylinder will generate more pressure.

Next I ensured that the front/back brake bias balance bar was set to 50/50 which means that I actually have front bias because the front cylinder is smaller. Note that I will add a an adjustment knob so that I can change the bias while the car is in  motion. I then positioned the brake pedal so that it was closer to the driver than the throttle to facilitate heal-and-toe shifting. I think it's right, but I won't know for sure until I drive the car. To achieve this I had to cut the threaded shaft on both the front and rear brake master cylinders. As can be seen in the picture to the right, the Jet belt sander does a great job at cleaning up the cuts.

Throttle Linkage & Throttle Position Sensor

Since the car is drive by wire (DBW) I purchased Titlton's throttle linkage kit. Like everything Tilton, it's very well made. However, I had an issue with the lock nut on the max travel stud hitting the bracket. I checked things out multiple times and figured that I could grind the bracket, but that didn't seem right for Tilton quality so I called their tech support and sent them some pictures. They called me back about an hour later. Apparently the holes in the bottom of the bracket are asymmetrical and the shaft had been installed backwards at the factory, thus moving the bracket slightly towards the throttle pedal. The picture on the left shows the asymmetrical bottom and the picture on the right shows the symmetrical top. After taking it apart and reassembling it everything was fine.

The bracket is designed for a Penny & Giles TPS280DP sensor. Apparently it’s a very nice hall effect sensor, tested to 60 million operations, 12-bit resolution, zero signal degradation over the lifetime of the sensor, sealed to withstand high pressure wash-downs (IP69K), dual outputs, etc.

All wonderful, but after spending hours of googling around I found all types of press releases, specs, etc., but no place to buy it online. After sending a bunch of emails to the manufacturer and re-sellers I received one quote: $250.04 and “approximately 6-8 weeks” delivery --  two months, really?

When I asked about the lead time for a replacement in case of failure, they suggested that I buy two! Clearly they forgot to mention that parts of it were made of unobtainium. After posting in the GT40s forum one of the members to me that Jenvey Dynamics white labeled as part number TP8LH. The LH indicates that the throttle value increases in the anti-clock-wise direction which is British for counter-clock-wise. In any event, I found an online retailer in the USA which offered it for $90 less.

Reservoir Connections

The reservoir connections were plumbed with -4 AN couplers and crush washers. The hose and fittings will be done at a later time.

Pressure Sensors

I replaced the supplied brake pressure switch with three high-end pressure transducers on the font brake, rear brake and clutch master cylinders. This will enable me to log the values and have the MoTec Power Distribution Unit (PDU) take actions based on the pressure. The connection required a special -3 AN Male to 1/8" NPT Female connector into the extra -3 AN port on top of the cylinders. The pressure sensor required a 1 1/16" wrench to tighten, which is the first time that I've used that wrench. Ironic that the tiny pressure sensor required a wrench much larger than all of the manly suspension pieces.

All of this resulted in a very clean installation.

New Friends

I've met a lot of great people chasing the SL-C dream and two of them, Will and Peter, stayed over for a couple of days to help out with the car. We discussed many things, found issues with parts and discovered some big challenges to think through. For example, the supercharger intake tube interferes with the gas fill tube (car kinda needs gas), the condenser was damaged during shipping, the evaporator won't fit due to the custom track-day bars, the banjo couplings on the brake calipers needs to be machined to fit BremboGTs which are much larger than the stock brakes, etc. Even these set backs represent progress because you can't solve them until you find them!

On the one step forward side, we cut an opening in the tail for the rear window. While the window hasn't been fitted yet, you can in the second picture that the carbon fiber vents have been fitted (but not installed). They are beautiful pieces and help mitigate one of the largest challenges with a mid-engine car -- keeping the engine cool. Cinder inspected them and she certainly thinks they're cool!

We were also able to get the majority of hard brakes lines and clutch line mounted to the chassis with some nice red clips from Made 4 U Products. The passenger-side rear brake line needs to be cut and flared for a better fit and the line running behind the fuel tank will need more clips installed, but that will have to wait until the engine is pulled.

Fuel Tank Mounted

It's important to isolate the fuel tank from the chassis to reduce stress and vibration that can lead to cracks or other failures. It's also critical that it stays put in the event of an impact or a roll over. It stores and 19.2 gallons which equates to about 116 pounds which, when multiplied by whatever Δv (hopefully small), means that you want to ensure that it's well mounted.

The tank is positioned as far as possible to the passenger side to provide better weight distribution when there is no passenger (I'm also a little heavier than my wife!)

I was going to fabricate brackets from 90° angle aluminum, but I found some nice ones from 80/20 Inc. They are clear annodized and gusseted for extra strength.

The self-adhesive rubber was cut to size and applied to the chassis and brackets. Two small brackets were installed to support the lower rear of the tank. Since they partially sit on welds, the bottoms needed to be machined for them to sit flat. Two large brackets were mounted on top of the tank and one large bracket was installed on the side of the tank to keep the tank from sliding to the driver's side (the passenger's side of the tank is stopped by the chassis).

I think that I'm going to install one more large bracket on the large cross member to prevent the top of the tank from tilting backwards, but I'll need to pull the engine to gain access.

Man Card Revoked?

Over vacation, whenever I was taking too long to get in the chilly ocean water, my daughter would threaten to revoke my man card. Today that got me to pondering,

"If I get as excited about garage cabinets as my wife does about kitchen cabinets, is my man card going to be revoked?"

I'm sure you're wondering what the catalyst was for this 'deep' introspection.. it was Joe from Motorhead Extraordinaire who installed a new set of Lista cabinets. They support 440 pounds per drawer and are what the aerospace guys use, so I did an appropriate number of Tool Man Tim grunts... and, yeah the man card is safe for today LOL.

The bench height resulted in the drill press being too tall (top right picture), so I cut the pole by a little over 8". I also had to modify the the table rack to fit in the reduced space. The 14" Metal Devil blade cut them both like butter... look how smooth the cut was in the bottom left picture (that's without any filing). I only needed to do minor deburring and beveling. Nothing like having the right tools.

Bubbles

Having cleaned the fuel tank and installed the fuel-level sender, the next step was to pressure test it. The tank has as a lot of TIG welding and if there’s a leak you want to find it before you install it and fill it with gas. I temporarily plumbed a Schrader value into the top left NPT port, a pressure gauge to into the top right NPT port and a  ½” NPT to -10 AN fitting with a cap in the bottom port. I pressurized the tank to 5 psi and went to dinner. When I returned the tank was down to 3 psi – I had a slow leak.

To find the leak, I mixed dish soap with a little water and brushed it on all of the seams. Fortunately, none of the tank seams leaked, but all of the NPT ports were leaking. I was surprised and how many bubbles a slow leak produced. I tightened the brass fittings as much as I dared, but they still leaked. While NPT threads are tapered, they don’t have a flare like you’d find in an AN fitting and they are often sealed with Teflon tape. However, Teflon tape isn’t compatible with fuel and if you’re not careful a piece might wind up in a fuel injector. Instead, I bought some Permatex Aviation Form-A-Gasket, applied it to the treads and no leaks! Next step is to install the tank.

Good Project for Hot Day

It was hot and humid which presented a good opportunity to remove all metal chips and dust from the fuel tank. The NPT openings were sealed with brass plugs and the fuel filler opening was sealed with this rubber end cap from Home Depot. The tank was filled with water via fuel-level sender opening and Connor was recruited help spill it out of the tank. The first rinse didn't result in any debris that I could see, but my OCD required that do it three times. Connor was having fun and he demanded that we do it a fourth time, so it's one clean tank.

When then tank was dry, I poured several cups of acetone into the tank and sloshed it around on all sides to remove any residue. 

The fuel-level sender provided in the kit is very nice. It is customized to take the unique shape of the tank into account and it measures capacitance so it has no  moving parts. The sender was mounted with five 10-24 bolts, #10 washers and the supplied cork gasket. Loctite 442 (aka blue Loctite), which is compatible with fuel, was applied to the threads.

Vacation and RPVs

I’ve been on vacation and I haven’t had any time to work on the car. However, I have been doing lots of research and ordering things. This of course causes a debate with my son when I try to get him off the iPad. He just doesn't see the difference between "research" and playing games.

Everything in the SL-C is low and the brake master cylinders are no exception. They are mounted below the brake calipers and gravity will cause brake fluid from the calipers to drain back into the master cylinder which causes excessive caliper piston retraction which results in a longer brake pedal stroke. To solve this problem, a residual pressure valve (RPV) is installed. A 2 psi RPV is firm enough to prevent fluid from flowing back but not so firm as to extend the caliper piston which would cause the brakes to drag. Since there are two master cylinders (front and rear) two valves are needed. The kit came with valves, but some builders have had issues with them leaking so I upgraded them to Wilwoods.

Fuel Tank: Part 1

I finally got around to removing the cage, interior tub and back panel to get access to the fuel tank. As with many Superlite parts, it's custom made and beautifully TIG welded. The pipe passing through the middle of the tank (you can see all of the way through it in the first picture) provides the straightest possible path for the shift cables... it's a mid-engine car and the drivetrain is behind the driver. It angles downwards from the driver side towards the passenger side.

The first step was to tap five 10-24 holes in the fuel level sender flange... and then start ordering lots of parts to start connecting things.

Seat Brackets

I wanted to see what it feels like to sit in the car so I installed the seat brackets. I'm likely going to upgrade to Tillet carbon fiber T5s in the future, but these will work for now. Comments at bottom of each picture.

Body Dolly

I removed the body today and built a dolly so that I can move it around. I was going to stand the sections up to save space, but I didn't want to store it in a way that might cause the body to deform. I also love looking at the car and I wanted it around to inspire me, so I built a whole-car dolly out of 2x 4's and 3/4" plywood sitting on six lockable caster. It raises the body a bit so it doesn't look quite as bad ass...

Note that I ran out of time and the nose and tail aren't sitting right... I'll fix that later. Can you find the dog in the picture below?

It's Here!

My car was delivered last week... about as good as Xmas morning when I got a Six Million Dollar Man action figure, a Guns of Navarone mountain and a bunch of military/automotive models. Reflecting on it, that’s a glorified doll, a multi-story doll house and models that required glue that causes brain damage if sniffed… what the hell were my parents thinking?

In any event, there was lots of tape residue on the car. The more options, the more residue. I did a bake off between Goo Gone, Goof Off and WD-40. Goof Off worked the best.

Father / Son Boondoogle

My son had vacation this week, my daughter had school and my wife was in Europe. What to do with a 10-year old? Take him to California to spend some time with the grandparents. For some reason I couldn't find a direct flight from Boston to San Francisco so I had spend a night in Detroit on the way there... so we went to the Henry Ford Museum.. and along the way we somehow stumbled into Superlite Cars / RCR...

MoTec Quality

The MoTec ECU, GPS transceiver and digital display were delivered today. The quality of the case is outstanding not to mention the display itself. MoTec appears to have their act together with respect to software and product modules. Many of the features in their embedded devices are activated via software keys. I assume the branded USB stick in the foreground does exactly that. It will be quite some time before I know for certain if MoTec is as good as their reputation, but so far I'm impressed.