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Electric Miata, my 2nd EV conversion

129K views 109 replies 18 participants last post by  Aboveliquidice 
#1 · (Edited)
Well I just bought a 1994 Mazda Miata for my next EV project. I am reusing parts from my last EV project, the Leadwing.

http://www.diyelectriccar.com/forums/showthread.php?t=58378

For those not familiar with the project it was a 1987 Honda Goldwing trike that I converted to electric mearly to learn and act as a stepping stone for this project. That project was based on some very good, but old 24V AGM aircraft batteries that I got a really good deal on. With 196V and 880amps available from the pack and only one small steering wheel the performance of the bike was predictably scary. All the local drag strips prohibited trikes so I was never able to see what I could get on the 1/4 mile. Anyway, this winter the parts from that project were harvested to go into the Miata. I had been scouring CL for cars for many months till I found this one. I was considering my 1969 bug but it is so original and such good shape I couldn't do it. Considered another bug, a fiat spider, and some others but there is an awesome aftermarket for the miata. Throw in disc brakes, great handling, reasonably safe and the fact that I could get one in good shape for $1300 and it was the final winner.
The project's goals in no particular order are:

1) A fair weather only car
I will commute in about 2-3 months during the summer. I car pool with my wife and as a school teacher for the other 9-10 months out of the year in our prius. Top down driving means no worrying about heat/AC.

2) Range of 35miles at 75mph down to 80% DOD
I can charge up at work so I am aiming for a minimum range of 35miles at 75mph down to 80% DOD. Realistically I will be averaging 65 on the highway but I want to be conservative. I will have to pay particular attention to motor cooling as 80% of my drive is at 60-80mph. I may have to go to a Warp11 or even dual 9"s but I am really trying to avoid this by minimizing aero drag where ever I can. I need to do more calcs but I'll probably start with my current motor and if I have to upgrade, then so be it.

3) 1000amps for 10 seconds
I want a pack that will make the most of my 9" motor and the Soliton1 controller. I would like to autocross and track it occasionally keeping in mind the impact it will have on my battery life. Aiming for 0-60 in 6 seconds but that will depend on how much weight I strip from the chassis.

4) Simplify and then add lightness
I have seen miata's down to 1600lbs with the stock motor and extreme weight reductions. No top and side windows for sure but I may go so far as no real windshield. It depends on how crazy I decide to get. Look at my last EV and it's pretty clear I don't want to build anything that is "conventional" :) I want a curb weight of under a ton but I'll have to work for every ounce.

5) $10000 Budget
The $8000 is for the batteries, BMS, instrumentation, and adapter, cabling, materials, etc. Given my other goals mean I have to go Lithium and a budget to match. Another 2k for a charger.

6) Have fun and learn
As a Mechanical Engineer who has spent over a decade in research, design and development "Have Fun" and "Learn" are one in the same. :)

My plan for the car is two stages:

Stage 1: Get it Running
A pretty straight froward EV conversion using the motor and controller I tested on the Leadwing. I will get it running and registered keeping the rest of the car pretty stock. Many other people have done miata conversions with adapters and mounts being available off the shelf. The big question for me (as is most converters) is the battery pack. Right now I am leaning toward some gray market A123 cells. Specifically the AMP20M1HD-A. I am talking with one guy and going to order a few for testing.

Stage 2: Get Crazy
The second stage will be stripping the car down to a fair weather only superlight speedster. No top, maybe even no windshield depending on how crazy I get. I will be replacing the front bumper with some custom fiberglass to get rid of the engine cooling scoop but I am toying around with a fiberglass front clip to save more weight. I will fab a real roll hoop/cage for protection. Without the constraints for a top I can make a cage that will provide real head protection. I used to run SCCA time trials and it would be fun to do so again.

First step now is getting the title transferred. I always do this FIRST when starting a project. I don't want to strip it down and then tell me I have to drive it down for a VIN inspection.
 
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#2 ·
Picture of the "new" car:
 

Attachments

#3 ·
And a couple pics for inspiration:
 

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#4 · (Edited)
Today my clutch kit arrived, aluminum flywheel, etc. I went with a Stage 3 becasue the electric motor can put out more then twice the torque as the stock engine.



This clutch and flywheel is the lightest I have ever held. The flywheel is only 8 lbs which is 33% less then the stock cast iron and I am going to lighten it up a bit more. :) Weight here is particularly important because it is mass rotating at <8000rpm. I was suprised that in all my searchining for deals on kits adding the flywheel only cost $60 more. It would cost me haldf that to have the cast iron resurfaced.




I don't need the starter ring so I am taking it off to save the weight.




Yes I am trying to make my flywheel cooler, but I am not making a pun. To help I threw it in the deep freeze. The aluminum shrinks much faster then the steel ring so this will give me a fighting chance of being able to get it off.

Now if only I knew where my motor adapter is going to come I would start ripping out the motor.... :-/
 
#5 ·
After 30 mintues in the deep freeze and 3 minutes of hammering, the starter ring is off. The flywheel now only weighs 5.7lbs. :)

 
#6 · (Edited)
No progress on the car as I am still waiting for my motor adapter. It is supposed to be done this week and at which time I will start ripping things out. But I have started the first steps on my pack.

Battery Testing

Last night I received a batch of A123 cells and I am starting testing. For those that don't know these are very good batteries that can put out over 20C and have shown very good life cycle in the labs at more reasonable discharge rates.


The problem is they don't sell to individuals, only OEMs. So the only way to buy them is on the gray market. There is a lot of speculation about how they get on the gray market; some are rejects that don't meet specs (usually slight low capacities) and many have had the tabs cut to make them difficult to use. The other theory is they are not selling as may as they planned so there South Korean factory is selling them out the back door without corporate knowing about it. Finally some are just outright fakes. But all of them have to be bought from China (since people will sell ANYTHING in china without fear of lawsuits). I bought 8 of them from my supplier to make sure they were good before going off and blowing $5k on the ~220 cells for a full pack. If these check out then I will use them to make up my 12V battery.




I am pretty confident these are real A123s that came out the back door given the serial numbers were sharpied out and some of the other markings.

Romulus Anode?




The first check with a DMM and not a good sign on three. The 3 cells with an extra sticker that says "Romulus Anode" have just over 2V. :( I am doing a 2 cycle charge/discharge on one of the cells right now so we will see how it comes out when I get home from work tonight.




FYI, Romulus doesn't refer to StarTrek rather it's Romulus, MI where A123 makes they anodes as opposed to the Chinese supplier they used before. I have been doing more research on the fabrication of these cells and it seems a bit odd. They are all labelled made in the USA but common knowledge holds that they are actually made in South Korea. I find it odd that A123 would fabricate components in the USA then ship to Korea for assembly and them ship them back to USA to assemble into packs. I would think they would manage their supply change better then that.


Test Cell




Here is my test station. A CellPro PowerLab 6 hooked to a PC. It's a bit ad-hoc right now as I can't find my other set of test leads and I have to do some more digging to figure out how to get the PL6 to go to 40amps instead of the 10amps I am limited to now. Even though I have selected a battery power source with 40amp max, the highest it will let me select is 10amps. Speaking of the power source it is a couple of left over 24V batteries from the leadwing project with a trickle charger. I am also using a book plus a battery to provide some compression on the sides of the cell during cycles. This evening I will make some improvements to the set-up.

 
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#8 ·
Building an EV is nice, building a 2nd EV is even nicer.

Where did you order the pouch cells? Did you consider already how to mount/package them?
I have a couple of people I am looking at weighing cost and risk.

My current plan is a stacked pack. Turns out very similar to A123's set-up but without laser welding. :)


Originally I was planning on 3 packs with just 66 cells in series but a BMS makes that less then ideal so I think I will be doing 3 packs of 3P11S. I am still working on the electical connection but am leaning toward a simple clamp and spacer system.
 
#9 ·
Well so far so good. The 2V Roumuls anode cell actually showed the highest capacity at just over 19ah which is much better then expected. Most people have been reporting capacities in the 17.5-18.5 range.




I still need to check the remaining cells since I only have a sample set of 3 so far. Right now I have cell #4 doing infinite cycles and I will check tonight and see how it is doing.

I still haven't spent anytime trying to get the software to go to 40 amps. Anyone have any suggestions? Doing it at 10 amps obviously takes 4 times as long.

One other thought I had is that there are several people on DIY forum that are testing these batteries from different vendors using the CellPro Powerlab6. If we all use the same test settings and post our data we can make a community pool of cell data that people can reference.
 
#11 ·
Since I am still waiting for my motor adapter I have been doing some work on the battery pack. I have tested the 8 cells I received and found the capacity ranged from 17.2ah to over 19.2ah. :( Not very good for building a balanced pack. I contacted the seller but have yet to hear back. We'll see what happens but this is exactly why I ordered 8 first instead of jumping in to the full 220. There are other suppliers of these cells that I am looking into so I have certainly not given up on them.

I did some prototyping of a pack by making up some end plates so I could band the pack and get good compression on the cells. Does anyone know how much pressure you need to need on the cells?

My design uses a .120 aluminum sheet cut and bent to serve as endplates. To make fabrication easier I made a plywood template for the flat pattern of the plates. I should have used MDF but I happened to have a correct sized piece of ply laying around


I then used a .25" carbide router bit in a normal router and now I can make a blank in less then a minute.


I made one up using some scrap aluminium I had laying around and the first tab I bent promptly broke off. I guess it's T6. :) So 30 seconds with the torch and I annealed it so I was able to bend it with hand tools. Not ideal but works for proving out the design.

Here is how the end plate looks on 7 of the cells I have.

I am going to do a bit of tweaking of the design and see if I get get some 6061-T0 otherwise I'll just aneall the stuff I have and make a prototype 1p8s pack.
 
#12 · (Edited)
The conversion begins

Well today the conversion started in earnest. I was waiting for my adapter and hub to come but I got the answer of "it'll be done next week" for the third time. I saw someone post that Electric Car Company could not get a delivery date right to save their lives and I am having to agree. :-(

Anyway I got tired of waiting and so I started tearing the car down. I wanted to have everything but the pack kitted before I started, but what the heck... I pulled the exhaust first along with the convertible top, emptied out the truck.


This was 131lbs removed from the car! I then turned my attention to the front where I pulled the radiator, A/C PS, headers, etc. I was surprised how relatively easy everything came out. It's nice not having every nut and bolt rusted solid. :)




So after 3 hours of work I now have the engine all disconnected and as soon as I locate a engine hoist I will pull the long block.



It helped having my 3 year old son "working" with me. :)


Another 75lbs of parts plus a couple gallons of fluid means I have easily dropped 200lbs that is not going back into the car.



One part I will be saving and reusing is the AC accumulator. It will make a good reservoir for the electric vacuum pump I am using for the brakes. It's a little small but it's light, has fittings and a mount already, and it was free.



Interesting thing I found was the AC compressor was MISSING. Something the previous owner blatantly lied about when he said the AC worked. :-/ There were quite a few things about this car that would have been a real pain had I not been converting it. You would think a Pre-Law grad would have had better ethics... never mind...

On the bright side a guy bought the stock catback for $50 (got to love CL) and I found a place that will buy the catalytic converter for $90 (scrap platinum).
 
#13 ·
Well this morning my wife and son were out doing the weekly shopping so I decide to tackle the removal of the fuel tank since the fuel vapor and torch are not 3 year old friendly. :)

The first step was draining the fuel tank and line from the lowest point I just bent down one of the lines from the engine bay and into a 5 gal can.




I then pulled the fuel pump assembly out which gave me great access to the tank. I used a hand pump to siphon out the last bit of fuel from the tank.




Then I filled the tank with soapy water. Make sure you leave the filler neck on so you can fill the entire tank. Luckily today was nice a windy so with the garage door open I had great ventilation.





The next step was removing the tank. It's held in with 4 bolts that are easily removed but the problem is to drop the tank you need to pull out the rear sub frame. So instead I decided to cut out the sheetmetal above using a oxyacetylene torch. I need the sheetmetal out anyway because I need the space for batteries. This is not for the faint of heart. I doused the area with water to minimize the chance of igniting the insulation but did have a few minor flare ups due to all the oil suck underneath. The pass rear diff seal was leaking and slinging oil everywhere. If you do this make sure you fill the fuel lines with water too. Again don't try this at home unless you know what you are doing.




I am draining the tank of water and will get around to start the fun part of yanking and cutting.




But that will wait for another day.​
 
#15 ·
One thing you can do to minimise the ah difference between cells is to match the paralleled cell to the ah average of your pack.

See this thread for more info: http://www.diyelectriccar.com/forums/showthread.php?t=67805
Thanks, I have been reading up on Electric Porsche's build and kakheath's. That is definitely what I will do but the wider the ah range the more challenging the matching. The way my pack is designed now I will be doing 2 packs of 2p100s which may make it impossible with this large range of capacity. I have one outlier in the 8 so if I through out that one cell the std deviation becomes much more reasonable. I am talking with the seller now about what he will guarantee as I can't eat 12% in "bad" cells.
 
#16 ·
BTW I did figure out why I couldn't get the 40amp charge discharge on my PL6. The FMA cable was pinned wrong the positive which was supposed to be on pin 9 was instead on pin 7. This is why I was getting a bad cell count warning. The tech support guy said they must have sent me a wrong cable (xh?) but a quick change and I can now overheat my "heavy duty" test leads at 40 amps. :)
 
#17 · (Edited)
Old engine out, just waiting for the new motor

Old engine out, just waiting for the new motor

Well today I pulled engine because I finally got a buyer for the engine from my CL ad. He bought it for $650 and the best part was he brought a engine hoist to pull the motor. It went pretty easy once I got the starter pulled.





I would love to install the motor but I am STILL waiting for my adapter from Electric Car Company International. I was told it would be delivered in less then a week and a half of payment. It has now been about a month and a half!!!! I knew I should have just built my own. Buying one was supposed to be faster and easier.... yeah right. It is supposed to be delivered on Monday, we'll see....




Until the motor adapter and hum finally arrives I have to sit in as the powerplant. Unfortunately my power to weight ratio is much worse then the 9" motor.
 
#19 ·
Looking good, man. I think you're gonna be solidly ahead of me, I'm pulling my engine next week.

Sorry to hear about your adapter plate woes, mine arrived very quickly from EV Source.
Thanks. I actually feel like things have been moving slowly because I have been working/traveling a lot recently. Hopefully I won't have to travel for work again until end of May and my adapter will be here tomorrow so I can start making more progess.
 
#20 ·
Armstrong power steering



Tiny update today. I did a power steering delete tonight. For cars this light power steering is really not needed. It will take a little effort in parking lots but it's really not needed. This saves me the weight , energy and and it's really easy. I have done this before on a 1987 BMW 325 track car I had for the 24 hours of Lemons, but that is another story...

Anyway there are several ways to do this:

#1: - Install a non-powered rack.
This gives it a factory manual ratio but you have to find a rack (which is not easy given the popularity of spec miata racing) and has a slower rate that helps in the parking lots but not so much on the twisties.

#2 - Depower the rack.
This is keeping your original rack and modifying it to operate manually. And there are two ways to do this the hard way and a really easy way.

#2a - Sealectomy
Which is to pull the rack apart and remove the internal seals and reassemble it:

http://www.flyinmiata.com/tech/depower.php

While it is the *best* way, I think it is overkill.

#2b - Plug and loop (what I did)
Here you start by plugging the ports from the power steering lines. If you just did this the steering would be very stiff because you are having to pump the fluid back and forth. To solve this, you cut the lines small lines that go from the valve to the rack and the turn the steering lock to lock to blow out the extra fluid. This will not remove all of the fluid so it will still lubricate the rack and pinion gears. To keep dirt, water, condensation, bugs, etc from getting it you put two short pieces of hose between so when you steer you just move air from one side of the rack to the other.



I actually reused some of the fuel hose I removed with the fuel tank. I know people that have done this to their miata's and 7 years later they are still going strong.

In the end it cost me $0 and took 15 minutes.

Simplify and add lightness. :)
 
#21 · (Edited)
One step forward, one step back

One step forward, one step back

The long awaited adapter and hub arrived today and for the most part it seems good except for a couple of issues which I will go into more later. I started by nailing a couple pieces of wood to my workbench to cradle the motor. The last thing I wanted was a 180lb chunk of metal to roll of the workbench on to my toes!


The adapter plate


The adapter is made of 3 pieces of aluminum plate that apparently have been water-jet cut. They are attached to the motor with 4 bolts that were included along with 8 flat washers (presumably to keep the bolt from shanking out) and 4 split washers. I normally don’t see plate this thick water-jetted because of the kerf from the jet fanning out. It is okay as long as you account for it by giving plenty of clearance to adjacent parts. I am not crazy about it for the mounting bolts but this plate is so thick it shouldn’t be a factor.


The first really issue is the hole in the plates for the hub is just barely oversized and the tolerance of the plate means it’s not quite centered on the shaft. Because there was so small of a gap designed between the hub and plate, this just bearly causes an interference. There is no play in the bolts mounting the plates to the hub so the hole in the plates must be opened up or the hub turned down (I think the best answer is both).

This really could have been avoided by making center hole ID (Inside Diameter) much bigger. All of that aluminum inside the 4 motor mounting holes is not doing any good. It doesn’t carry any load and is just dead weight that should have been just put into the recycle bin for the machine shop to get a few bucks back.



One last note on those split washers. In this application they are useless because you have to use the flat washers underneath them. Split washers only *work* when they make contact between the base part and the fastener. I will be using Loctite to keep these in place.

The hub


The design of the hub is… interesting. It looks like part of a cast shaft coupling that screwed into the actual hub by 3 M10? socket head cap screws. These screws alone would not be sufficient to carry the repeated +200ft-lbs torque of the 9” motor but since the coupling appears to be wedged in (kind of like a taper lock) when you clamp it up it should be strong enough. The hub is also larger in OD (Outside Diameter) then it needs to be which like the ID of the adapter is un-necessary weight and leads to the interference above but also causes a interference with the flywheel. The flywheel has a recess that would normally go around the end of the crankshaft. The hub is considerably larger OD then the original crank so it does not fit inside.

I am going to email Electric Car Company and we’ll see what they say. I am sure they will fix the issues but it's a matter of how long it will take. I have a feeling I may be borrowing some lathe time soon to turn down the hub OD and opening up the plate IDs myself just to make it happen faster.

One other issue is I don’t have bolts for the flywheel. :-( This is 100% my fault because I should have resused the ones from the engine. But I left the old clutch and flywheel on for the guy who bought the engine as he was converting from auto to manual. Oops.
 
#22 ·
Maybe you can use the other three holes in the adapter to install dowel pins? You'd want to be sure that those never crept out and gouged their way around the motor bearing... but it would more than double your torque capability.

Is there anything on the three waterjet-cut plates that registers them together, and centers the motor and transmission using the OEM dowel pins and the motor's bearing end register? If not, you can easily be far enough out of alignment between the motor shaft and the transmission shaft to cause long-term bearing life issues. The typical alignment error on an OEM engine to transmission bellhousing is under 0.005" (that's the maximum runout limit suggested by Lakewood) and probably more like 0.002".
 
#23 ·
Maybe you can use the other three holes in the adapter to install dowel pins? You'd want to be sure that those never crept out and gouged their way around the motor bearing... but it would more than double your torque capability.

Is there anything on the three waterjet-cut plates that registers them together, and centers the motor and transmission using the OEM dowel pins and the motor's bearing end register? If not, you can easily be far enough out of alignment between the motor shaft and the transmission shaft to cause long-term bearing life issues. The typical alignment error on an OEM engine to transmission bellhousing is under 0.005" (that's the maximum runout limit suggested by Lakewood) and probably more like 0.002".
The lack of registration is a concern of mine as well (among a few others). There is a reason the original engine had 2 large dowel pins that engauged the bellhousing, for alignment, just as you said. Then add the tolerance stack-up of 3 plates that are waterjet cut and it's no strech to think it could be out as much as .030". Measuring the misalignement of the hub to the input shaft isn't easy though...
 
#27 ·
Motor Dry Fit!

Motor Dry Fit!



Well I am still in discussions with Electric Car Company about my adapter. I just heard from Steve at Rebirth that a adapter from them will be a 7-10 day lead time. Lesson learned...

So yesterday I pressure washed the 178,000 miles off grease of the car so when I work on it I don't look like a coal miner. :)


And tonight I deiced to go ahead and dry fit the motor without the hub. I first needed to layout the motor cradle so I found a short section of heavy wall 1.25" pipe that had a nice tight fit over the input shaft. This allowed me to measure the height and see that the cradle fit really well if I welded it to the sub-frame.


The cradle is the same style I used on the leadwing. It's actually a mount for large high pressure cylinders (9" OD) in military ships. It even comes with a warranty plate circa 1988. Either way it is very stout, comes with all the hardware, and was $30 for two of them shipped! :)

It will need some modification but for now I just tacked it into place to dry fit the motor.



I am glad that I went with the 9" motor as once I put on the adapter on the assembly weighed over 210lbs! This really wasn't bad to lift, carry and man-handle into place, but if I had a 11" (~350lbs) I would have definitely need a hoist.



Anyway the motor fits in really well. I am going to trim the cradle away some before I weld it all in as I think I can lower it about another 1" to give a little better CG. Seems excessive but this is the heaviest single item on the car.



You can also see the the great space in front of the motor for one of the pack modules (with the help of my assistant). I was originally planning on splitting the pack into 2 modules but it would be a little too long. So I am going to do 3 instead to fit between the the frame rails.
 
#28 ·
Controller fitting


I also test fit the controller. That Soliton1 is such a great piece of eye candy that I couldn't tuck it off into a corner. So just like on the leadwing I am going to put it front and center. I am considering 2 options: This first is mounting it parallel to the motor. Looks nice and would be fairly easy to mount.



And a 4 year old in thedriver's seat making motor noises makes it even better :)

I might even put it in a bit of an angle just to show it off more and get a little more clearance in the front for the pack.


The other option is to put in perpendicular. I am planning on putting in a strut tower brace so it would be REALLY easy to mount the controller and it hides the wiring by pointing toward the firewall. But it doesn't look right.... I'll do some more head scratching but I am leaning towards putting it in long way. I think if I did it sideways it would be a detail that would bug me.


Of course every knows that blowing bubbles on your controller is good luck for an EV....


If only the adapter was correct I would be really close to hooking up a few SLAs and driving arounf the driveway....​
 
#29 ·
Getting the charge on the charge card

Getting the charge on the charge card



A bit of an update on the project. I haven't done much on the actual build due to the adapter woes but I have spent a fair bit of money.

I ordered and received my batteries! 250 A123 cells with full tabs. I really wonder when the delivery driver looked at the shipment he had thoughts of being used as a drug mule. :)



The bad news is my PL6 died but the good news is the warranty replacement is supposed to arrive Monday. Once it arrives I will start taking data and post the results here:

http://www.diyelectriccar.com/forums/showthread.php/standardized-pl6-testing-a123-cells-and-71283.html


I got my cable and crimper and connectors so I can start making up my cables. I was able to find a good US made bench top manual crimper, new for a decent price. Luckily for me the seller didn't do a good job of describing it on ebay and it took 30 minutes of websurfing to find out exactly what it was. http://www.uzengprod.com/ I wanted a crimper that, when used with the right terminals, would be UL listed and would have at least 3 crimp points. I did some searching and found most lug install specs require a minimum of 3 crimp points (NASA says 4 but this isn't a spacecraft :) so that eliminated all of the cheap crimpers except the the Chinese green lee hydraulic knock offs. I will gladly spend a few extra buck for an American made product.


The connectors are new Molex lugs and the cable is very good 2/0 bright orange cable (safety requirement for first responders) that I ordered from Trystar. I like to buy in bulk and so I have enough to do 4 or 5 cars. I am thinking about offering to make cables for whom ever doesn't want to go out and buy a good crimper and do it themselves. When I did the Leadwing I used a battery cable company but they were pricey for cables over a few feet.
 
#30 ·
Not-so Adapting Adapter

Not-so Adapting Adapter



I emailed Electric Car Company and told them I was returning it for a full refund and asked for a return shipping label. A few days later I received a return shipping label but no other communication from them. I mailed it out and hope to get my refund soon. BTW that adapter weighed in at 28lbs!

So I went ahead and ordered the performance adapter from rebirth auto since they said 7-10 day turn around.

http://rebirthauto.com/mazdamiatamotoradapter.aspx

 
#32 ·
Re: Not-so Adapting Adapter

We use those adapters in our miata conversions, it is a work of art, you are really going to like it. The full floating coupler eliminates all kinds of issues.
Mike
www.EV-propulsion.com
Yeah, I have no doubt I will be happy with it. Everything I have seen says they are a good group of guys and have many happy customers. Sometimes you get what you pay for (at this price I certainly hope so. :).
 
#33 · (Edited)
Wait! Weight?!?

Wait! Weight?!?



Well with the car down to a roller I decided to see what the weight was. Lesson learned from prototyping aircraft is to follow-up and check the weight periodically to avoid the surprise of having a 200lb useful load. :) The weight always creeps up and you have to deal with it, this car was no exception. :(

Unfortunately I never did get it to the gravel yard to weigh it before hand but the published curb weight is 2400lbs. Now that 2400lbs doesn't include any options and my donor was fully loaded with PS, AC, AM/FM/CD, leather seats with built in speakers, etc. I have been weighing all of my parts as they come off the car with a bathroom scale. I have been doing it in boxes so that the accuracy errors don't add up (errors are rarely linear). I did not weigh the engine I removed but research says it should be about 300lbs wet. I also did not weight fluids but everything else was accounted for:

3/15:
Exhaust: 36.2lbs
Spare Tire: 22lbs
Top and Frame: 34.6lbs
Top parts, rear compartment panels, rear carpet: 38.2lbs
131.2lbs removed

3/17
Radiator 17.6lb
Airfilter and Misc: 12.2lbs
Header and downpipe: 18.0lbs
PS + hoses, AC (partial), misc 24.6lbs
72.4lbs removed

Engine: 300lbs (est)
Fuel tank and hoses: 27lbs

630.6lbs removed (ERROR should be 530.6)
2400lbs - 530.6lbs = 1869.4lbs

Now how to weigh my roller? Well I could spend $1700 for a nice set of race scales that I would but under all 4 wheels but I don't have that money to blow so I went for a cheap solution. I bought 2 scales with a 440lb weight limit for $25 each (you can find them on sale for $17 sometimes).

http://www.amazon.com/gp/product/B00472I1V2/ref=oh_o01_s00_i00_details

Now based on a few tests I would say the scales are accurate to ±5lbs but that is good enough for my for the car weight. So to avoid exceeding the max weight I put a 2x6 across the 2 scales and recorded both weights. I jacked up each corner and got 4 weights, one at a time.


FL: 248.6+220.0=468.6lbs
FR: 264.2+220.0=484.2lbs
RL: 293.6+212.8=506.4lbs
RR: 286.7+222.0=508.7lbs

That puts the roller weight at: 1925.9lbs :( I am 75lbs over my estimate of where I should be today

Now adding up the weights of my other parts the weight will be ~2800lbs at in street form. Well above my final target of 2204lb (1 metric ton) but I do have some more weight reduction (heater, air conditioning, stereo, lighter seats, windows.....). That 1ton goal is for a very stripped down version but all this doesn't fully add up since I know of people with ICE powered NA miatas at 1800lbs. Part of the weight increase is I have upped my pack size.
BTW I apologize for using the antiquated units, my old scale was in lbs but from now on I will be recording in the proper units, SI.

Hopefully next week I will have my PL6 battery tester back and a motor adapter so I can make some real progress.
 
#34 ·
Re: Wait! Weight?!?

Wait! Weight?!?



Well with the car down to a roller I decided to see what the weight was. Lesson learned from prototyping aircraft is to follow-up and check the weight periodically to avoid the surprise of having a 200lb useful load. :) The weight always creeps up and you have to deal with it, this car was no exception. :(

Unfortunately I never did get it to the gravel yard to weigh it before hand but the published curb weight is 2400lbs. Now that 2400lbs doesn't include any options and my donor was fully loaded with PS, AC, AM/FM/CD, leather seats with built in speakers, etc. I have been weighing all of my parts as they come off the car with a bathroom scale. I have been doing it in boxes so that the accuracy errors don't add up (errors are rarely linear). I did not weigh the engine I removed but research says it should be about 300lbs wet. I also did not weight fluids but everything else was accounted for:

3/15:
Exhaust: 36.2lbs
Spare Tire: 22lbs
Top and Frame: 34.6lbs
Top parts, rear compartment panels, rear carpet: 38.2lbs
131.2lbs removed

3/17
Radiator 17.6lb
Airfilter and Misc: 12.2lbs
Header and downpipe: 18.0lbs
PS + hoses, AC (partial), misc 24.6lbs
72.4lbs removed

Engine: 300lbs (est)
Fuel tank and hoses: 27lbs

630.6lbs removed
2400lbs - 630.6lbs = 1769.4lbs

Now how to weigh my roller? Well I could spend $1700 for a nice set of race scales that I would but under all 4 wheels but I don't have that money to blow so I went for a cheap solution. I bought 2 scales with a 440lb weight limit for $25 each (you can find them on sale for $17 sometimes).

http://www.amazon.com/gp/product/B00472I1V2/ref=oh_o01_s00_i00_details

Now based on a few tests I would say the scales are accurate to ±5lbs but that is good enough for my for the car weight. So to avoid exceeding the max weight I put a 2x6 across the 2 scales and recorded both weights. I jacked up each corner and got 4 weights, one at a time.


FL: 248.6+220.0=468.6lbs
FR: 264.2+220.0=484.2lbs
RL: 293.6+212.8=506.4lbs
RR: 286.7+222.0=508.7lbs

That puts the roller weight at: 1925.9lbs :( I am 175lbs over my estimate of where I should be today!!!

Now adding up the weights of my other parts the weight will be ~2800lbs at in street form. Well above my final target of 2204lb (1 metric ton) but I do have some more weight reduction (heater, air conditioning, stereo, lighter seats, windows.....). That 1ton goal is for a very stripped down version but all this doesn't fully add up since I know of people with ICE powered NA miatas at 1800lbs. Part of the weight increase is I have upped my pack size. I knew it will be a struggle to get that low, but that extra 175lbs will make it virtually impossible.

BTW I apologize for using the antiquated units, my old scale was in lbs but from now on I will be recording in the proper units, SI.

Hopefully next week I will have my PL6 battery tester back and a motor adapter so I can make some real progress.
I was contemplating doing the same thing to weigh my 944 but didn't have anything suitable at the time to level the opposite side of the car. I'm not sure how you did yours but if the other 3 tires are flat on the floor your results will be a bit "heavy". For it to work properly you should have 3 spacer blocks the same height as your scales + 2x6 so that the suspension is always at the same height on all 4 corners. Then you just trade a spacer block with the scale set-up to measure each corner.
 
#36 ·
Well, I was wrong. Unless you consider 12% to be "in the noise"

FL: 80.2+76.6=156.8kg
FR: 103.4+85.4=188.8kg
RL: 97.7+80.7=178.4kg
RR: 74.4+109.7=184.1kg

Total=708.1kg=1561lbs!

That is a 200 pound difference and means I am 25lbs under where my calcs say I should be. This is only ~10% lower then my first measurement but it makes a big difference. I did do a few measurements and found it was repeatable within a couple kgs. The real answer will be when I weigh it finished but it's good to know I am on the right track (pun intended).

Thanks!
 
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