On second thought ...

After thinking about how to handle the torque transfer from the drive axle to the sprocket cassette, I decided to go the more difficult but more elegant route. I had intended to use a kart hub to handle the torque load(previous post) and afix the cassette housing to it -- also sleeving the shaft a bit since the cassette's ID was slightly bigger than our axle.

After sleeping on it I decided that I would build an indexing jig and spline the shaft itself. By custom milling both the keyway and the keystock, I could size the keys to handle both the radial loads and the torque.

I started with a round piece of plyood and using my previously contructed hub holder created a indexed wheel.

I set up a little marker system off to the side of the mill table and used this to locate each spline location on the axle. Milling ensued.

Custom milling the keystock.

I left enough room in the keyways to move the sprocket group back and forth for perfect alignment. The shaft collars are only used to keep the sprocket from sliding back and forth on the axle.

Next ...

Our first tests with the vehicle will be on a dynamometer where we collect data on the prop at static thrust (wind speed). We will also use the vehicle as a 'dynamic prop stand' by running it (push or pull?) up and down the runway in still air at different speeds, collecting data from our instrumented hub.

Before we build our two spools for the spool transmission, we want to make sure we get our gear ratios optimized. I ordered up a large recumbent bike sprocket for the prop shaft (65t) and purchased a 9 speed cassette for the drive axle. This will give us a selection of ratios to work with. Additionally, the chain drive will be our less efficient (we believe) backup transmission if our spool drive adventures don't play out.

The next challenge will be to mate the cassette on the left to the hub on the right. Not exactly sure yet how to get that done ... thinking cap on.

One way out

We don't have a differential on the drive axle -- too heavy for our tastes and besides, the vehicle is designed to pretty much stick to a straight line. We still need a way however to ensure we aren't binding as we drift around off the straight and narrow. We also need a one way device on the prop shaft to keep the prop from backdriving the transmission (especially the spool transmission) if we get a sudden wind shift.

The solution was three ratchet hubs that will mate up to our kart axles. Of course as has been the case with most of the parts on this vehicle, no one seems to stock DDWFTTW ratchet hubs anymore. After about 16 hours (12 in the first one and 2 hrs each in the others) I finally finished them up this evening

Construction details in previous post.

When you have more time than money

(Or to put it another way ... what to do when DDWFTTW Vehicles R Us is out of stock on ratchet hubs)

To make the ratchet hubs, we again started with standard kart hub blanks.


Previously, I searched around and found a ratchet box wrench that I felt would handle our torque needs and was also reversable. We'll use the reversing feature to allow us to tow the cart around free from the transmission.

After putting the hub on a diet, I milled out a shape that matched the shape of the wrench head.

I grabbed a square swatch of aluminum for a lid -- drilled, tapped and cap screwed it on and then milled it round to match the hub.

I ground off the handle of the box wrench and installed three set screws to use for centering the wrench in the hub.

Once I fit, centered and locked in the wrench head with the set screws, I mixed up a small batch of epoxy and heated up the assembly (so the epoxy would flow). I let the epoxy fill up the space between the hub and the wrench head to make a nice, tight, torque resistant fit.

Here's a shot of the three in a progressive state of assembly.

Second chances

At the last group design meeting we all decided that the SJSU students would build a second propeller. They'll come up with a different design optimized for slightly different conditions and then we'll have another choice come test days.

The students spent the weekend working on test templates and practicing foam cutting. They are sharpening their hands-on skills on this cheap foam in preparation for the more expensive Spyder foam.

Their first task after this practice will be to make a test prop section about 2ft long with twist, taper and a spar. They will glass and sand this section as if it were part of the final prop. This test section will give them experience with every aspect of the construction and then they can go after the final product.

Here's a few shots of the guys cutting, shaping and sanding the test templates.

Here they are hot-wiring out some foam.

Three's a crowd

Finished the three brake disc hubs and mounted the discs to them.

They won't all be side by side as shown here -- I just slid them on the axle to shoot the pic.

Can we stop this?

The first three hubs I'm modifying are for the braking system. We're using three mountain bike disk brakes mounted to these hubs. There will be two on the drive axle and the third will mount to the propeller shaft.

Following is a sequence of shots I took last night from the process -- reduce hub size to something more appropriate, drill and tap the hole circle to match the disks and then install said disk.

Please hold me

As we're using kart axles to spin all our bits, we have quite a number of kart hubs that we need to modify to fit our various components. We're fitting bicycle disk brakes rather than kart brakes (too heavy), three freewheel ratchets (one per wheel and one for prop) and of course our actual drive components (sprockets, spools, etc. depending on the phase of the project.

Using the milling maching, I carved out a working fixture from delrin that bolts to the indexing table and accepts the kart hubs and allows them to be held for machining.

Where the rubber meets the road

I'm not pleased with how many hours we have in them, but I'm very pleased with the results.



We should have the remaining parts for the Prop hub in today or tomorrow and that's where we'll go next.

Never too late to learn

How many wheels have I trued in my life? This one and one more will make two.

Speed

The Faster than the Wind Team would like to take a moment to thank our primary sponsor Joby Energy. Not only have the folks at Joby generously given of funds and advice, but they have also allowed us to accept associate sponsorship from a company whose very business is based on speed.

Welcome aboard Google. Thank you for supporting our search for DDWFTTW.

Is it true?

The first wheel is all laced up, but our custom hub isn't going to fit any truing stand that's readily available -- so as with most of the project, we'll make our own.

I'll probably build the other wheel before I start the truing. It's a rather time consuming process so perhaps I'll set up where I can tweak on them while watching the NFC/AFC Championships tomorrow -- two birds, one stone.

Don't take me half the way.

50% of the spokes in, 50% to go.

It's too little to lace

Loading the hub up with the first round of spokes.


Installing the 'key" spoke.

Apparently the online spoke calculators aren't all that accurate when it comes to unusually large hubs -- once the leading spokes were in place, the trailing spokes were too short to lace in. Off to the bike shop to see if we can scare up a couple of extra millimeters.

Rim Shot

Two Velocity Dyad 29" rim blanks -- the toughest tandem bike rims on the planet we are told.

Get in the groove

Short spokes and a wide hub make for a nasty bend as the outer spokes leave for the wheel. A bit of a groove rolling towards the center creates a smooth path for the spoke. (yes, I had to lace the wheel up before figuring this out. Sometimes you must go backwards to go forwards)

My what big hubs you have!

With the work on the initial prop winding down, we're out of the garage and back into the shop. The milling machine will be the center of activity for the next few weeks as we churn out the custom drivetrain bits. We'll start with the drive wheels.

We decided to use 29" bike wheels as there is a good selection of heavy duty (tandem bike rated) components available. Unfortunately, we didn't feel like a standard width hub would give us the side loading strength we needed. Bikes lean for turning and thus other than asymmetric pedal forces, they don't get a lot of lateral loading. Narrow hubs work fine in that application, but our vehicle doesn't lean when it turns. Additionally, we need to transmit force to our axle whereas a bike hub rotates in its axle. The solution was to pick up racing kart wheels and modify them to create a hub that suits all of our needs.

We started by facing off the front and back of the kart wheels so there would be a flat area for the spoke holes.

With the wheel clamped to the index fixture, spoke holes were drilled every 20 degrees around the rim.

Here's a comparison with the original.

Last but one

The penultimate layer -- primer on both blades.

Fix these broken wings.

We got our prop spars for free (windsurfing masts) because they had been broken. We considered wrapping the damaged root sections of the spars with glass fabric to reinforce. We finally settled on cutting sections from two other broken masts and glueing them into the ends of our prop spars. This will ensure that our hub clamps won't snap the spar.

Here's a rough rendering of the instrumented prop hub. The 4 large shaft collars in the center are the interface for our carbon prop spars. The bronze colored object is the thrust bearing which presses on three radial load cells. The two paddles on the back transfer the torque through two load cells to the hub itself.

Tell me if I turn you (on)

As we ramp down on the prop portion of the project (we'll show a final series of pic soon), it's time to start moving forward again on the chassis components.

We've spent quite a bit of time considering the instrumentation of the vehicle -- what sort of data streams would be valuable and how we would use them. We decided a while ago to build an instrumented propeller hub but spent more time than we would have liked choosing, locating and matching the parts to make that happen.

Through the magic of Ebay we finally picked up 8 affordable load cells. These cells are not exactly what we needed for all locations, but we have the ability to mill them, modify them and make them work on our budget.

We'll radially place three of these cells near the front of the hub to measure prop thrust, two will be placed at the back of the hub to measure torque and down below we'll build two into the frame of the chassis to measure the resistive force being place on the wheels by the ground. From these three streams we'll be able to derive prop efficiency as well as overall power transmission efficiency.


We had to figure out how to get our data off our spinning prop hub. We preferred to have access to this data 'real time', rather than storing it on the hub for later download.

In our real business, we work with a Canadian RF design shop regularly- Pacific Design Engineering (http://www.pde.com/). They helped us locate an off the shelf RF solution that will do the trick and then they generously sent us a sample to use on the project.

THANKS PDE!!

We'll be programming and testing this telemetry system over the next few weeks.

In the end, these are the data streams we plan to be logging on the vehicle:

propeller thrust
torque applied to prop hub
prop shaft speed
retardant force on drive wheels
drive wheel shaft speed

Additionally, we'll be measuring and logging GPS plots and relative wind direction and wind speed at three levels on the vehicle -- low, center and top of prop. We'll likely use digitally instrumented pitot tubes and will place these well in front of the vehicle and out of the region of prop influence.

Repeat as necessary

Building up the layers of glass. 3 per side.

The Professor's evil creation

Young Propenstein at work late at night in his evil lair.

The cooked foam episode

It's cold here in the garage. Resin likes about a week to cure in the cold and we don't have a week for each layer. Between us we have three 500w work lights so we fired them up and kept them around near the foam. We carefully monitored them to make sure they weren't too hot for the foam and got away with it for a day or so.

Next time you're building a DDWFTTW vehicle propeller in your cold garage and using quartz work lights, here's a little tip -- turns out that the last 5 minutes of the bulbs life, right before it burns out, it produces MUCH more heat than normal. We had a light that had been in the same place for hours and hours with not a problem (all the way back to the day before) and all a sudden we noticed that there was a blister on the foam and then 'poof' the bulb went dark.

After this episode, we went to Lowes and bought a propane salamander heater to bring the garage up to temp without risking the foam. We were able to sand out the blister and fill the void, but it could have been a lot worse.

Getting rid of what's no longer needed

Each foam section had 'legs' in the back that were the reference steps for the twist fixtures. Once the top layer of glass was holding the prop in shape, we flipped the blades over and with Rick's custom foam 'scissors' we hot wired off these legs and then sanded them smooth.



When we glued the foam sections onto the spar, the resin leaked out and ran down each seam on the back of the prop. This gave us a hard 'line' at each seam that didn't want to sand easily.

After a few different attempts, we finally found that a small sanding drum on a dremel tool could be used to lower the level of each seam below the desired surface. We'll then fill these seams and sand them level.

Home from the Holidays

After a couple weeks of only sporadic effort, the new year has brought the team back together again. School break for the SJSU students still has a week or two left in it (we have a team meeting coming up after they return on the 14th), but Rick and I have resumed work on the propeller in Rick's garage.

After putting one layer of glass on the front side of each prop blade to create some structure, we removed the twist fixtures from the table and built a couple of clamps sets. These grab the spars and allow us to rotate both blades for sanding and the remainder of the glassing.

The first of many

We've now started the rather long and rather laborious process of adding layer after layer of glass to each side of the propeller blades. We're going one layer at 0degrees and then one at 30d and one at 60d.

Here's the first layer of the first side of the first blade. While there will be no more 'shaping' on this blade, there will be a fair bit of trimming and sanding between layers.

No, it won't make the Honda Insight go DDWFTTW

With both blades of the prop bonded to the spar, we had our first chance to see the general look of the entire prop assembly.

One half is filled, shaped and sanded while the other is rough.

Rick putting the finishing touches on one of the blade shapes before we start wrapping it with glass.

Rick got the tapered aluminum spar extension (formerly a ski pole) glued into the carbon spar bushing and the final sections bonded. A bit of filling and sanding and we're ready for glass.

We learned today that for some reason, the glass fabric that we've had on order for a week or so was not shipped. A bit of a delay that we weren't expecting.

Just another Silicon Valley garage project

For the next phase (assembly and layup of the prop) we've had to move venues. With what we've got going at work right now, we don't have the space in the lab to leave the assembly fixures up for a week or so straight. We moved to Rick's garage for a bit.

Here are the first 5 segments evened up and glued. As you can see, the carbon spar ends at this juncture and there is a tapered aluminum spar which goes inside the carbon and continues on out through the smaller sections.

The holes you see along the top of the airfoil are where we poured the resin to saturate the spar/foam interface. The binder clip hold the trailing edge nice and even while the resin cures.

It's all on the table

Ready to glue in the spar.

Coming together

Starting to assemble the segments on the twist fixtures.

Sliced prop

Finished hotwiring the sections mid-afternoon.

It's a big one.

11 of 16 segments complete. We'll get the rest tomorrow.

We've got it wired.

Spent the day carving blue foam with the hot wire. Got 11 of 16 segments completed.

Nothing sticks

Bob Parks turned us on to some adhesive teflon tape that facilitates smooth hot wire movement across the templates.

After the practice rounds with the cheap pink foam, I think today we're ready to go after the blue foam for real.

Update at 11.

Practice makes ... incremental improvements

We put in a rather short day yesterday and did a bit of cutting practice on cheap construction foam. We had to glue two layers together for some because our pink foam is only 2" think.

We're hoping that we can get our cutting skills up to par before we throw down on the $250 chunks of blue foam.

Here's a root section and a section from about 2/3rds of the way out.

Checking alignment

Looking down the spar cavity.



Spar check.

First look

We finally got all the ribs on their stands and aligned in a proper row. It was our first chance to see the general shape of the prop in actual 3D.

All in the family

Here's a shot of the entire family of templates. Just behind them are components of the stands that will locate and align them on the build table.

The longest template chord is ~20" and the cord of the tip template is barely 2" long.

Smooth around the edges

The airfoil templates will guide the hot wire through the foam core section. The thin wire tends to catch on the fiberous edges of the plywood and if the wire pauses against the ply for even a moment, it will burn a groove in the wood.

You can make templates out of phenolic sheet or other dense and heat resistant materials, but we don't expect to use these particular templates more than once so we went the cheap route.

I sanded the edges with 600grit sandpaper and then trimmed them out with aluminum tape from the HVAC supply. The wire slides much better and a pause won't burn a groove nearly as fast. It's not perfect, but it's darn affordable.

Rick sent me a few profiles to post.

These are based on a 450lb vehicle/pilot weight. A Crr of .02. Frontal area of 20sf and a Cd of .3. Transmission efficiency of .8 and the prop thrust numbers from JavaProp.

We believe we can do better on some of those above numbers, but also we don't expect the prop to ever be quite as good as theoretical. In the end we think we can get quite close to the below.

Where's Waldo?

Somewhere in this block of blue Spyder foam is hidden a large propeller.

Picked up this slab yesterday and hope to have it in many curved pieces by the end of this next weekend.

Occasionally something turns out to be easy

We've been a bit concerned about how easy (or hard) it was going to be to get our foam accurately cut to fit our spars. As previously mentioned our spars are tapered carbon windsurfing masts and while these make almost perfect structural members for our prop, we were unsure as to how accurate we could mate the foam sections.

After laying out our build table with all the template positions, we transfered those marks to our spars and calipered the cones at those locations. We then made up a set of test templates designed to produce a hole in the foam to mate to the conical spar. If after the cut, the foam slid on too far or not far enough, we would then employ the method of cutting the blocks long and trimming them to length after the hole was cut. Rick had a far higher confidence than I that the foam would stop right on the mark when we slid it on.

Rick made a 'foam drill' from a piece of thin wall tubing and I modified the hot wire bow to allow the wire to quickly connect and disconnect. We threw the templates on a scrap of foam, drilled the pilot hole and pulled the wire from the cutter through the pilot.

After hot wire cutting out the plug we put it on the spar and it slid right to a stop on the mark. One less complication to worry about. We will cut our blocks to length and wire cut the airfoil and the spar hole in one operation.

Here's a shot of our test insertion.

Scott Nix donated two more masts

The team would like to thank local windsurfer Scott Nix for donating two carbon windsurfing masts to the cause. These two are particularly nicely matched, and will likely be used as spars for prop #2 in the reasonably likely event that our first effort comes out looking and working like a first effort.

Thanks Scott!

The plots thicken

Here are some 2D and 3D plots of our first production propeller design.

Though we have allowed room on the cart for a 20ft prop, this one is a 16ft. The windsurfing masts that we are using for spars allow for a very clean and simple 16 footer without needing any extensions at the root so we're going the easy route first round.

It's likely that we'll build more than just this first one. We'll put this one on the test stand and dyno, document it's actual performance curves, compare them to the theoretical and decide whether it deserves an actual test on the cart.

If we're careful enough during construction we might just pull it off with one, but as we've never built a prop of this size before, we're learning as we go. Both construction wise and performance wise we'll use what we learn on this one to improve round 2 if needed.

Religious symbols

Well, it's one thing to design a propeller -- it's another thing entirely to figure out how to get the design templates to print out properly and to scale.

We finally imported the points into my CAD program as survey data and faked it into drawing a line between all the points as if it were drawing contour lines on a topo map. Four hours (and countless sheets of 11 x 17 paper later) we finally figured out how to get it all scaling and printing.

We ran out a couple samples, glued them to our template material and whacked away on them to see what we thought. I think we'll be pretty happy once we get them sanded perfectly.

The tabs you see on the templates will sit on blocks located on our build table to get the alignment and twist correct.

The final product looks a bit like those Jesus fish with legs that you see on bumpers occasionally. Perhaps we'll be blessed.

A table for 2x

We've spent the last couple weeks working on our prop design. Rick's got a good handle on that now and we are close to starting construction on the template/ribs/etc. We'll post up some of the airfoil and performance plots in a bit.

Today we spent the day making up our build table. It has to be very straight and square so we can put our reference lines on it and also bolt guides to it etc.

Rick came up with a slick little set of adjustable braces that allow us to take any twist out of the table and still let us fold it up and put it against the wall when we aren't using it.

Here is Rick putting the last screws in the piano hinges before we put the legs on and turn the table over.

Table on it's feet for the first time.

A close up of the little adjustment bracket that I milled slots in. Loosen the wing nuts and slide the triangles relative to each other and the top twists/untwists.

Turns out we didn't need that.

As previously mentioned, we weren't exactly sure how the torsional stiffness of the chassis would be affected once we got the front steering assembly welded and installed. We suspected we could remove the front former altogether.

Once it was all bolted in we did a torsional load test, removed the front former and repeated the test. There was no difference between the two tests. The welded front assembly provides enough torsional rigidity that the front former is uneeded. Out with it.

Point us in the right direction and turn us loose

Rick and Steve spend Saturday running Java Prop sims on different prop sizes, planforms and airfoils. They're looking for the right balance of RPM and efficiencies that will give us the best transmission/prop combo and also have an airfoil sized right to accept our windsurfing masts as spars.

I spent the day welding and mounting up the steering fork for the front wheel.

The (almost) finished product. I haven't mounted the tabs for the wheel hub because I want to wait until we actually get the hub in our hands. I like to do things only once when possible.

Once we mount up the hub/wheel/tire, we'll decide whether we steer directly with our feet or with a linkage back to a stick.

Having a busy week at work so there's not much evening activity going on cart wise. We did spend a couple hours last night adding the composites to the center chassis former.

It was going to be a bit of a pain in the ass to use the carbon tow in this short space so we grabbed a few yard of unidirectional carbon fabric and wrapped with that. We again finished over that with one layer of 5.8oz glass to protect the brittle carbon.

Next up ... I'm going to weld up and install the front steering mechanism and wheel support. On it's own this will add some stiffness to the front portion of the chassis and after it's installation we will determine if the front former is just stiff enough, or needs composite layers added, or can be removed completely.

We build a set of crude headstocks so we could wrap the prop pylons by spinning them. It was a ton easier this way rather than looping the spool around and around like we were forced to do on the chassis itself.

Here's Rick starting the windings.

100 layers of carbon tow on each pylon and a layer of 5.8oz glass later:


Before the wraps we did a torsion test and recorded the results. Once this cures I'll publish the pics showing the before and after tests. Hopefully we added a good bit of stiffness.

We received the 'correct' steering bearings today.

Cheap Chinese bearings are easy on the wallet but sure can be a pain in the a** sometimes. These are supposed to be for a 3/4" shaft, but as you can see the .738 ID is going to require me to do a bit of material removal.

Oh well, 5 minutes work with the grinder and we'll have a .737 steering shaft. :-)

Tested the sample of Qpower line that we received. Stretch and strength as advertised and as expected. So far the stretch characteristics of Kevlar, Spectra/Dyneema and Vectran have all be similar - well under 1% under our proposed loads.

This product has a thin woven sheath and I feared that this would add a bit of 'squishy' to the end result. I was pleased to find that under load, I could do the usual gentle caliper measurement and then squeeze very hard and only get a .001 or .002 difference. Pretty happy with that as the sheath will up our durability - though it does add another layer on the reel due to the diameter increase.

I'm pretty sure that this line will be the line that we use to test the spool transmission for suitability.

The students had a presentation due today relating to the project. I dropped in to catch it in person and on video.

After their 15 minute presentation, they were grilled by other students and the Professor regarding various aspects of the project.

There was a bit of stage fright going on and I can certainly relate.

The bearings arrived for the front steering mechanism. I was waiting for these before welding up the front steering fork and mounting brackets.

I ordered the right bearings and this was reflected on the packing slip --- but they sent the wrong ones. These things happen.

Should have the replacements in by Friday.

Holloween Workothon

A few thousand wraps of carbon tow, a bit of of glass fabric on the bias and a quart or so of epoxy resin later ...

Holloween Workothon

Foam on and ready for carbon/glass wrap.

Holloween Workothon

I worked on cutting and tacking up the parts for the front forks and steering mechanism. The bearings should arrive today so I'm going to wait for them before welding up everything for good. Check twice, weld once as they say.

Holloween Workothon

Dat and Aung worked on cutting, sanding and fitting up the foam to the chassis pieces.

Holloween Workothon

With our layup plan now in place, some of the gang showed up Saturday morning to help with the chores.

Chris helps Rick disassemble the frame in prep for lamination...

... and ends up at the whiteboard talking transmission theory (or some other brainteaser ...with Rick you never know).

It was testing time for the chassis beam samples that we laminated a few days ago.

First the bare control sample: it weighs 4.5lbs and ~9 degrees of twist. That's a 30lb weight out 24" on the arm.


Next the fiberglass sample: 5.5lbs and ~4 degrees of twist

Finally the fiberglass/carbon combo: 5.7lbs and ~2 degrees twist.

So, it's settled ... will will use the fiberglass and carbon combo. 5.8oz cloth and 70 layers of 12k carbon tow wrapped diagonally.

.

For those of you wondering why we're using the labor intensive tow rather than using carbon fabric, it is mostly because we *have* the tow already -- we paid $60 for 16,000ft of it as potential tranmission line, but it failed for that purpose. Rather than spend near $500 for carbon fabric we will do a little hand wrap work and save both money and weight.

Going in for the easy layup

Aung, Dat, Sheetal and I were up till around midnight last night laying up the torsional test samples. It was quite an adventure as we had to MacGyver a hot wire rig together. Since we have quite a bit of foam cutting ahead, today we'll work on putting together a better wire setup. Aung and I cut this foam by pulling on a wire between us while Dat bravely held the wire to the terminals of an RC starter battery.

The one on the right has just one layer of 3.7oz glass and the one on the left has about 20 diagonal wraps of carbon tow under the same layer of glass. The control is in the center.

Saturday morning they will be cured and we'll test against the control. I'm betting there won't be a dramatic difference between the two and that neither will be stiff enough without another layer. But then, what the heck do I know?

We're drillin' for oil

We had our weekly team design meeting today and just so everyone could get a feel for the scale of what we were doing I clamped all the primary chassis pieces together for viewing. When they imagined the tip of the prop another 10ft above the prop pylon, they were better able to see why the cart has the width and length it does. More than one commented that it looked like an oil drilling derrick.

The rear axle cage that you see here is only for dyno testing -- the one used out on the runway will be twice as wide. The prop stand you see there is 12ft high and is sized for a 20ft prop. Those tall pylons will be faired out to a long airfoil shape for low drag. Even at only windspeed, those pylons get a lot of airflow from the wash of the prop so they need to be sleek.

Bob Parks was at our meeting and over the next few days will be helping us determine if we will be building a 20ft prop or one as small as 16ft turning a bit faster. The larger prop is more efficient on it's own, but gearing losses on a slower turning prop can erase those gains. He's going to help us find the most productive balance.

Before we laminate the foam/glass/carbon on our chassis members, we want to build a test fixture and run samples to optimize the layout for best torsional rigidity vs weight.

We will save one of these pictured samples as a control and layup the other three in varying combinations of glass and carbon. We will then test the three for the best stiffness/weight ratio and against the control to see if any of the three give us the improvement we need. If none of the sample are rigid enough, we will go another round of composites over the existing layers and test again.

We hope to have these samples/tests done by the end of this weekend so we can then start layup on the chassis proper.