2009 05 08
So far still only preliminary exercises. To see what I'm working towards building see the Freeranger info page
I Handcarved a roughly 1:3 scale foam plug of the bottom section of the car yesterday to do a test of the process of foam shaping, coating, glass laying,resin, maybe body filler and sanding, mold release and negative and positive molds. Also to eventually gain some insight into the twist stiffness of the hull and how many layers of fabric is needed to gain the necessary strengths. It's 120cm and 30cm wide which is a little less than 1:3 scale. The height is 1:3. Because the foam will dissolve by the resin I plan on painting it with a waterbased paint and hopefully that will make a barrier that will leave the foam intact when glass cloth is laid on.
A couple of weeks back I got the motor from Ebay (350$). The now discontinued original 9.5kg Briggs&Stratton Etek permanent magnet brushed DC motor that was used for their outboard boat motors. The Lynch design can be pushed to around 50Nm and 40HP which is a nice power density. Unfortunately it was clogged with styrofoam dust deep within the motor in ways I wouldn't think possible. The Ebay seller forgot to mention they got it that way and also forgot to include the sprocket shown in their picture. It took about an hour to clean it with a wire hook and a vacuum cleaner and they were nice enough to send me a sprocket without charge so I gave them positive rating anyway.
I ordered a Skyway Tuff Wheel II 20" carbon fiber reinforced plastic wheel originally from the BMX world (100$). Seems nice and sturdy but probably a bit too visually small for the 4 meter long car so I'll probably get the 24" version which unfortunately isn't commonly available in the carbon version. The bearings in the hub is for too small an axle for my side mount so that will need some custom work for larger bearings and disc brake mount for the front wheels.
One of the first items I bought (besides power electronics way back) were synthetic leathers and EVA foam to get a feel for the way I could make interior looks credible. There seems to be a nice selection and a particular black fabric that resembles the typical car black dash leatherlike surface. I don't use real leather as I'm vegetarian and I shall not kill. I did a simple test with 6mm EVA foam on cardboard with a V groove cut and the leather glued on just to see how I could give it detail that looks intentional. Also bought a couple of square meters of glass fiber plain weave cloth and some polyester resin to do initial tests. I've also found a source for cheap bulk cloth and resin for later. It's surprisingly inexpensive, ironically because the resin is made from fossil fuel.
Also acquired a socalled Freehand Router hotwire styrofoam cutter where the wire is stiff enough to shape to whatever form you want to cut. It cost 40$ and I was too cheap to buy the power supply with it. I might regret that.
There's also some bondo type polyester body filler, some mixing cups, mixing sticks and also the PVA release agent that's a liquid that dries into a plastic film for separating the part from the mold. Very useful. Hopefully much more to come but all depending on funding.
2009 05 11
I did a test to see if normal water based base paint could protect the styrofoam from the polyester resin. I painted two areas of foam with a thin and thick layer of paint respectively.
After drying I mixed up a bit of polyester resin with about 2% hardener and applied a sloppy layer to the two patches and a bit above to see its effect on uncoated foam. Polyester contains the organic solvent styrene which is very fleeting and continuously comes out of its unopened container. Seemingly can't be contained and is not entirely healthy. It has a distinct smell.
Although it spent the night outside in maybe 8 degree celcius air and hotter air could have cured it faster, the result was too problematic to be relied on as a method. Even the thick layer of paint didn't adequately protect it as seen below. Interesting to note a small patch of preserved foam.
Next I'll try a few tests with multiple layers like car paint on water paint or EVA film on water paint or just several layers of water based paint. Also only a thin coat of polyester and heat it to limit the time it's corrosive.
2009 05 12
Second round of styrofoam protection coating tests. I painted 3 patches with the water based base paint and let it dry. Then one patch was painted 1 or 2 times again. The other two patches were painted with car spray can paint and PVA liquid mold release agent film respectively. The PVA is normally used for coating a mold before casting so you can separate them again after drying. The PVA is intended for use with polyester resin so should presumably hold against it. I did a previous test with PVA directly on the foam but it just seeped into the foam.
All 3 held up fairly good but the PVA was the clear winner with virtually no erosion. I had expected more from the spray can paint but it didn't do much. That area might have had a bit more resin on but still can't compare to the PVA coating. Interestingly enough there were a couple of potholes under the surface where there had been pinholes in the coat but with fiber cloth draped over it at the same time it should be ok. Worth avoiding though if possible.
I used a higher concentration of hardener for this mix and it might reduce the cure time so it's less straining on the protective coat. Hopefully it wont strain the PVA more when the next layer of polyester is applied. I use chopsticks to mix the resin with, works well and is commonly available. The PVA release agent I use so far is a german water clear product but often it is colored deep blue so you can see where you have applied it.
Next step is to try it on the model and if it works put a single light layer of glass fiber cloth on it to give it a bit of strength for later application of polyester spackle (like bondo) and sanding.
2009 06 07
Testing the protection coatings and subsequent glass laying on the hand carved scale polystyrene foam model. I first painted the foam twice with the water based primer and after drying I applied 2 layers of the PVA liquid release agent film which is the protective layer that keeps the polyester resin from eroding the foam. I only have 1x1 meter glass cloth so I have to apply two pieces because the model is over 1m long. The first piece I test draped over the mold without resin to see how it would drape and it hugged it fine with a bit of stroking.
Rather than wetting the mold with resin first as is recommended to avoid trapped air pockets I decided to try to just wet it through the cloth to avoid having to position the cloth over a sticky surface. It wetted fine with a paintbrush. I bought an aluminium roller but it was useless, it just rolled over and left a lot of excess resin. The paint brush left only the needed amount and applied soft pressure so the glass clung to the shape nicely like a wet T-shirt. Unfortunately the brushes die when the resin hardens. Not sure if they can be cleaned before hardening or if it's even worth it. The finished result shows the cloth structure on the surface which tells me that I didn't apply too much resin that would otherwise add weight without great strength. The real strength is of course the glass. It's not important for this test model but is important for a full scale with several glass layers. I used 150gram resin and around 125gram of cloth in play (50x100cm piece overlapping).
I had originally intended to apply the rear piece too but the 150gram resin only barely covered the first so I let it cure. Later I did the last piece but with that mix I waited a bit too long and the resin suddenly gelled on me and it couldn't be applied. It just sat there like a piece of jello so I only got a bare minimum of resin in it. It should be enough for the purposes of this test as there will be polyester body filler applied over the surface later to allow for sanding down to a nice smooth surface and subsequent top coat. The foam was only roughly hand carved but for a serious model that could be sanded so much less body filler would be needed later.
The next step is applying the polyester body filler spackle, same as bondo, and then sanding and then final coat that hopefully will be smooth and shiny. Not sure if that will be a car paint or maybe another type of top coat.
2009 06 16
I've been working on the combined rear suspension and drive train design. It's not easy having to commit to a specific design that actually has to work well and make sure all the elements are existing products so it can actually be built. It was suggested to me to use socalled chromoly steel or chrome molydenum because it has high tensile strength at around 5-700MPa compared to 300ish for normal soft steel. Of course that had to be hard to get here in Denmark so it took a lot just to find a supplier for that. It's basically a tube frame of 16x1.5mm and 30x1.5mm tubes and some 2mm plate here and there. The sole central pivot is a dry plastic bearing bushing from german GGB on a 10mm bolt. It should have reasonably low friction coefficient and it's a low speed joint so it was chosen over a more elaborate roller bearing setup or weaker Heim/Rose bearing. To keep the design simple I went with a rigid suspension arm and also to serve the single wheel arm outer design. It's a compromise compared to a more conventional double wishbone suspension as seen on most racing carts like formula 1 which has a nice vertical travel but often has many more members out in the wind and a very strained shock absorber arm or a shock out in the wind. The double wishbone would also require at least 2 universal joints which require high precision of manufacture or it will strain a lot when the suspension travels. Seeing as I have to build it all and noone has the vision to support it, I like to keep it simple.
The motors are coupled in fixed gearing using a #40 standard chain from a 13 to 60 tooth sprocket giving a gearing of around 1:4.61. The #40 chain has a load rating around 3600N and breaking strength around 4x that which should be enough. The motor will peak at no more than 50Nm and at 25mm torque arm on the small sprockets that's only 2000N tension on each chain. Having two light motors allows for this unique rigid arm suspension and saves me the differential. It might not be the ultimate design but worth a shot I think. The drive shaft is made from the same 30mm chromoly steel with heads welded to either end and held in place by a 30x47x9mm ball bearing at either end. The large sprocket is to be mounted with a 30mm keyed hub that should be able to handle the around 250Nm peak torque. The critical area of the design is the high bending stress point on the two main tubes just under the shock absorber mount. Still haven't done the math on how thick the tube walls have to be to be sure to last. Options are 1.5,2 and 3mm.
Below you can see the whole suspension arm moving the wheel 62mm above ground which is so far the nominal maximum deflection. There will probably be room for as much as 100mm suspension travel should it be needed in an emergency. The rest is up to the tire and body flex. It should be plenty and overall I'm quite happy with the design even though it's far from complete. The shock absorber is 170mm from eye to eye on 10mm axles and the spring will probably be around 550lb/in for around 3g tension at nominal deflection. The 3g is from what human legs experience under running conditions so it's a hunch :)
The 9.5kg Etek motors are mounted close to the arm pivot line so they are not directly unsprung mass even though they are rigidly coupled to the wheels. Their movement is considered quite acceptable.
2009 06 21
Mini update. Due to supply difficulty of the chromoly tubing the tubing has been changed from 30x1.5mm and 16x1.5mm to 32x2mm and 20x1.5mm which is also stronger. The supply is so tentative that it might change again. I may have to reach out to german producers directly for any dependable supply. The temporary bottom hull has been made 4mm thick and a hole has been cut for suspension design purposes. The hull is not the final shape and only roughly bent into place to suit the suspension. I am also wondering if it's too wide for a single person width so the middle section might also change. I've added upper structure of the rear suspension for the shock absorbers to push on. They connect to the hull high on the sides and there are thin tension tubes down to the central pivot points. The pivots would otherwise just flex the bottom too much. The hole to the outside will likely be covered by some rubber membrane so it's almost closed but still able to flex. It's not easy to see in the picture but I've also added near correct models of the large sprocket which is two part, a ring with the teeth and a hub so the design is not only a computer model but possible to build from available parts. The upper parts weigh about 1770g and the two suspension arms weigh about 6kg each without motor. With motors the rear suspension and drivetrain has a calculated mass of about 32.8kg which is quite a substantial part of the target 100kg total weight of the car without batteries.
Next is the front suspension which is expected to be lighter.
Being aerodynamically designed it's not entirely coincidental that the bottom hull looks like a boat and since it will be nearly sealed it's interesting to speculate if it could sail on water :) There is also a sister design idea where it flies..
2009 06 25
I did the front suspension in a first draft that could work though without the wheel mount and wheel pivot or disc brakes etc. The rack and pinion isn't there either but is supposed to be placed between the drivers' feet and the suspension pivot. Same single arm premise that the rear suspension uses just much simpler without the drivetrain. It's inspired by the simple suspension seen on some electrathon eco racers.
2 second video here
The seating seems to pan out nicely and the steering column will be two piece with universal joint going forward and then down between the feet of the driver. The legs will be more spread and the longer the legs the wider the spread of the knees. Both pedals and seats are so far intended to be in fixed position. Only the back of the driver's seat can tilt forward to let the passenger in.
The middle section of the hull will likely not be roll stiff enough so I may have to put a 10mm aluminium honeycomb plate on the floor of the cabine which will also make the floor firm to step in on.
Instead of the large nuts on the fix plates of the suspension it might also be possible to just have it bolt into the plate from the outside so it can be much smaller and more elegant. It depends on whether that can be depended on to stay put or if they will slowly unscrew which would be bad :)
2009 08 30
Quick update on the battery placement.
This is the intended placement of the battery pack and a likely configuration of 24x16 cells of 26650 LiFePO4 power cells, possibly A123 cells. a combined capacity of 3kWh in a 24s16p config of 80V37Ah resulting in an estimated range of around 100km. Weighing a bit under 30kg it can deliver around 1000 Ampere sustained enabling Ferrari beating acceleration if the power electronics and tire grip can handle it. The 80V is a top speed of 140km/h with current gear ratio and wheel size.
If this arrangement is chosen I might try connecting them with soldered on copper sheet instead of the more common welding of nickel strips. Not only is copper a better electrical conductor but soldering is easier to do with home equipment. I might use a flame solderer and compressed air cooling after to keep the heat damage to the cells to a minimum.
A chinese battery seller OSN power tech, claims to be selling genuine A123 cells from an alleged chinese A123 factory. I have been quoted 3.7$ per cell in volume of 10000 which currently must be considered a very interesting price for A123 cells. I've ordered a couple of cells to try to determine if they are indeed first rate A123 cells or not. Alternatively there are some chinese brands of 26650 cells that deliver quite good power levels, comparable to A123 and similar price. DLG (aka K2), Baoding (aka Valence) or a few others.
The above image is generated with software I programmed.
2009 09 03
I've been looking into part's sourcing, steering wheel and dashboard instrumentation among other. There are quite a few after market steering wheels and some are fairly nice looking. They range from the more elegant computer game steering wheel to the more ricer/tuner/ridiculous power ranger look. There are many on ebay at quite low prices (20s of $) and even more when looking directly at the business to business sites like alibaba because all the cheap ones come from china anyway. They are surprisingly cheap with prices ranging all the way down to 6.8$ for a nice complete steering wheel for a car, even with a central button for the horn. I'm a vegetarian but they even have real leather steering wheels at less than 30$. I bought the below 32cm one on ebay which looks fairly nice and I'm looking at a couple of similar 28cm ones as samples directly from china. A normal car has a 35cm steering wheel so it will have a tighter sportier playstation age feel I think. Gotta be new and fresh, not old dull, overweight and dead.
It would be nice to have an airbag in the steering wheel as well but that's too ambitious for this stage of the project.
I also received the 2 chinese allegedly A123 sample cells I ordered from the bulk seller OSN power tech which promises that they are genuine and offer bulk pricing as low as 3.7$ in volume of 10.000 or 4.5$ in more manageable volume. While I haven't tested their inner resistance or capacity they do weigh the right 72gram (valence weighs 84 gram for instance) so at least they got that right if they are fakes. It looks the part too so I'd guess they are actually real A123 but second sorting as they've also admitted although the exact story is still unclear. They are probably a good candidate for a pack since I don't need the full killacycle effect.
I also bought some black synthetic leather today at a local fabric store that I've long had in mind for the dashboard surface. It has a very nice touch and look-quality and should very nicely serve as a credible dashboard finish as well as perhaps for a two color seat pattern. It should also go pretty well with the dashboard instrumentation unit I've found from ACEWELL which is a Taiwanese maker of aftermarket motorcycle computers. It's a CD sized all-in-one neat package that has the blinker indicators as well as the backlit display needed for night time driving. Speed, rpm, trip and odometer. Although not cheap at 150-200$ retail, it's a nice way to get up to speed on required instrumentation in a not ugly package. They are made for combustion vehicles of course but I was willing to live with having to adapt the fuel gauge to battery monitoring but when I contacted the factory for an OEM price they responded with a new version specifically for electric vehicles so if that's in production it might be an even more perfect solution with an actual battery state guage and forward, neutral, reverse indicators.
A 12v 10$ horn component (a car needs a horn) as well as a key have also been sourced from the 2-wheeled industry at a local store so the parts supply is shaping up.
2009 10 14
I continue to apply for funding from various agencies but so far still no luck. I spend many hours preparing the material and they spend a few seconds of ignorance on saying no. On the one hand they don't see all the thoughts I've had to arrive at the design but on the other hand they don't seem to try to understand either. I'm afraid most of them are rather mediocre people relying on quite unfortunate selection criteria such as their mediocre vision for the future which is a half baked meddly of the ignorant press and the disinformation of the opposition like big oil and they seem to hang their hat on 'safe' things like university names and municipal projects, giving no thought to the actual merit of the projects. To compound the problem they have blind faith in their own judgement and the process is entirely closed and not subject to appeal.
On a happier note, I got the 2 38120 10Ah sample lithium iron phosphate cells from 'Advanced battery factory' that are allegedly capable of 30C discharge and very long cycle life. They also have very practical screw terminals which make pack assembly much easier. They included the little rails to connect them and while I expected that to be a cheap metal it turns out they are actually 20x1mm plated copper. I'm positively surprised. Headway aka Zhejiang Xinghai Energy Tech also make a cell that looks identical and they quoted me 12.4$ per cell. These might well be headway cells, I can order some samples and compare them. If they have anywhere near their rated performance it's a very good candidate cell. 96 cells (24s4p) would give an estimated 100km range and weigh about 33kg.
I also got my first steering wheel, a 32cm ordered from ebay in France. The mazda logo can be taken off but the grip material is harder than it looked so it might not be ideal. It looked like soft synthetic leather but it's basically a hard plastic cast. I've ordered another 28cm steering wheel directly from a factory in China (they cost less than 10$ and 20$ if you want real leather!). I might order yet another 30cm from another factory. I've also maybe located the manufacturer of the airbag steering wheels used in the Mini, Opel roadster and maybe also in the Tesla Roadster and I have inquired about a price from them. It would be nice to have an airbag.
Today I received my custom made ACEWELL 3802-E speedometer and indicator instrument. It looks very nice although for OEM use it would be nicer without the factory logo, especially the bright color. But fine for now.
All black as requested instead of the cheap looking silver look plastic edge they normally use. The indicators on the sides are also color neutral plastic and only the light is colored which also help make it look more sophisticated. I haven't powered it up yet, it requires a 12V supply but should look very nice once the blue display comes to life. Set in a shaped dashboard and draped with the black synthetic leather in the background it should look quite professional.
Dan Frederiksen (df at zev.dk)