Weber and Coulomb's MX-5

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Post by EV2Go » Tue, 20 Jul 2010, 16:48

IMO I think you would be pushing the friendship with the engineer if you mounted batteries in the trans tunnel.

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Post by Johny » Tue, 20 Jul 2010, 16:49

Did you guys do the whole car in Sketchup? You are GODS!

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Post by AMPrentice » Tue, 20 Jul 2010, 16:51

Looking a real beautiful project thank you for showing us all
the details and keeping us up to date with all the intricate aspects.
Im just thinking out loud at perhaps some things that might allow other
battery positioning options.
Have you considered running a torque tube like say from a Peugeot 505
and alloy indepedent centre as this would allow you to run batteries above
the tailshaft tunnel without interfering and in fact offer better arm rest position.
Not in the transtunnel but sitting above it.

Also a tapered angle reverse bonnet scoop or more like the standard bonnet raised
at the windscreen end with filled in sides would also help aerodynamics by removing
the dead spot between the end of the bonnet and start of windscreen and hopefully
allow extra room for batteries. The following pic is a sample of the bonnet mod
it can be done by most Frg places for around 600aud and will need air dam or bumper
mounted lights to rid the horrible and space robbing pop up lights.
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Post by EV2Go » Tue, 20 Jul 2010, 17:02

Not wanting to rain on your parade but I don't think the bonnet scoop would work as an aero mod either. Back in the days when that sort of scoop first appeared (mid 70's in Australia on SLR 5000 Toranas) the design used the windscreens turbulant air to feed the engine bay (when hole was cut in bonnet), so all it did was hit the screen and turn back under the scoop it didn't actually help any air pass over.

If you could find a way for the scoop to sit up against the glass (or very close to it) there is a good chance it might work, but that would require a bonnet that flips forward.

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Post by AMPrentice » Tue, 20 Jul 2010, 17:27

Also when you look at the percentage of where the most amount of time
is spent on commuting (if thats what this car will be used for mostly)
and the street then it will see 0-60kmh most of the time.

Im aware of that principle encountered in many other track exercises
but the one you use as a comparo Im afraid is like apples and oranges.
The Torana reverse scoop was a monstrous tacky brick of a scoop
sitting quite a distance from the screen. Not to mention the rest
of the car including the bonnet is no where near the shape of a miata.
A convertible needs all the help it can get around the winsdreen and
this is where Corvette Stingrays and Cobras had similar issues.

This is the tunnel mod I was trying to explain.
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Post by coulomb » Wed, 21 Jul 2010, 02:55

Johny wrote: Did you guys do the whole car in Sketchup?


I'll give you a hint... the steering wheel is on the left hand side in the model.   Image
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Post by weber » Wed, 21 Jul 2010, 03:19

Hi ap^Hmprentice. Thanks for the ideas. I don't think we want to get into having new body panels made, since we've already bitten off more than we can chew in several other departments. But the above-the-transmission-tunnel idea may have legs.

We often joke about having to put cells in the ash tray, and that's where the ash tray is. I figure we could fit about 9 cells there, sloping down from the roll-bar cross-beam (above the parcel-shelf) and stopping just short of the gear lever. This will be good for when we add the extra 18 cells to bump it up from 228 cells to 246 cells.

What's that you say Coulomb? This is the first youve heard of it? You're still recovering from when we went from 208 to 228 and had to squeeze in all those extra cells? Image

I note that 246 * 3.65 V = 898 V.
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Post by weber » Wed, 21 Jul 2010, 03:39

You think you've seen fuses before? These are fuses. In fact I feel safer addressing them as Mister Fuse.



Image



Trouble is, they are too expensive to ever blow, so we're gonna have to protect them with some kind of vacuum-contactor-based circuit breaker. Image



That's sometimes euphemistically referred to as "backing up the circuit breaker with a fuse" Image



They were $127.50 each (ex GST), from Swe-Check. And the posts they are mounted on were $64.30 a pair. Including GST and freight that's AU$438.46 in my hand there. They can break a 100,000 amp arc at 1000 Vdc. Except I think the s/c current of our cells is only about 1000 amps.



Here's the datasheet with the time-current curves.



[Edit: Added link to datasheet]
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Post by AMPrentice » Wed, 21 Jul 2010, 03:43

Great place to have an ashtray, imagine it falls on your crown jewells!
I suppose if you guys down the line find the bonnet and pop lights deletion
could help you with image trademark of your EV and for extra space,
the first one is the pricier one at around 600 while the following are usually 400 aud these prices I got quoted at most places using all factory hinging.
They are such a small car its definitely a huge challenge.
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Post by coulomb » Wed, 21 Jul 2010, 03:51

Back to trying to understand why I can't talk to the charger over the CAN bus. When I send what I think is the right CAN packet, there is a brief communication with the charger once per second. I only seem to read 3 characters at 2400 bps, and they don't correspond with the CAN packet, and they're not consistent.

So I needed a CRO that I can trigger at the start of the pulse train. I recently attempted to spruce up my old valve CRO, but it's got a way to go before it's ready for this. This EV day we opened up Weber's dual trace CRO, which went pop the last time we turned it on. After looking around for exploded capacitors or burned resistors or transistors, we settled on the high voltage circuit. The diodes here are unlike any I've seen, like a tiny rough football shaped mess of ceramic not much thicker than the pigtails. They seemed to measure open circuit both ways. I even got out my 3 V battery pack with resistor that I use for BMU testing, and the diodes did not conduct even with 3 V across them. We replaced the 3 V battery with a 9 V one, and low and behold, the diodes conducted (with negative on the side with the red stripe) with about 8.5 V drop. Wow, there must be a stack of diodes in series inside there!

After cleaning off some flux and general dirt and grime, we decided to turn it on. Nothing like fresh smoke to track down a fault. Low and behold, there was no smoke, no drama, and a trace came up. Image

Well, that was a fairly easy fix. I applied the CRO to the RS232 signal I generate from the charger signal on pin 6:

Image     Image

Please pardon the quality of the photos; I don't have a decent tripod. You can see that my crude RS232 converter isn't coping well with the narrow pulses; the fall times are rather long. Only 4 pulses; seems weird. Also, that stage at the end where there are no pulses, can't be real RS232, as there are no stop bits.

So I looked at the input to my crude RS232 converter... oh. Many more transitions. Looks like my crude RS232 converter is a little too crude. I'll try some sort of push-pull circuit next.

Well, the CRO did its job, telling me that my RS232 converter is bad.
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Post by weber » Wed, 21 Jul 2010, 05:47

Coulomb started mounting the Pot Box last Tuesday. We finished it today. It's a Hall-effect job from EVWorks. Coulomb had a great idea about using a wire clamp from the hardware shop. It happens to fit the existing hole-spacing of the pot lever perfectly. We first tried it on top and then found it worked better on the bottom.

Image

Image

Image
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Post by coulomb » Wed, 21 Jul 2010, 14:52

I would add that we used a 3 mm cable clamp from Bunnings; they come in various sizes with 3 mm being the smallest. Even that was a little too large for the accelerator cable, but a little grinding allowed the U-bolt part of the clamp to sit lower against the main body, and then it clamped the cable quite well.

Edit: we cut about half the thread off with a hacksaw, to clear the body of the potbox at full throttle. But we possibly needn't have done that now that the clamp is on the other side of the lever. Naturally, we put the nuts on first, so we could use them to clean up the thread a little after cutting and filing.
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Post by Jeff Owen » Wed, 21 Jul 2010, 16:51

Surely some form of toggle should be used to reduce flexing of the cable as the pot box arm swings over.

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Post by weber » Wed, 21 Jul 2010, 19:08

Hi Jeff. It is a flexible wire-rope type of cable, as you can see in the first photo. I don't understand why anything more would be required.

Incidentally I just heard from Ultramotive that they have the steel billet the new flywheel will be made from. So I've just dropped off to them the existing flywheel and pressure-plate and a 2517 taperlock bush and hub for reference.

I also dropped off our induction motor's rotor. They will bore the hole in the drive-end of its shaft to take a bronze bush as a plain bearing to support the end of the gearbox input shaft. And they will turn down the non-drive-end to 25.4 mm to fit inside an 1108 taper lock bush that will be used to couple the pulley for the aircon and power steering.
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Post by AMPrentice » Wed, 21 Jul 2010, 20:23

those fuses look like sticks of dynamite and wow expensive :(
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Post by EV2Go » Wed, 21 Jul 2010, 20:29

sorry have to agree with jeff...

Although it is a flexable wire rope type cable I have performed more than my fair share of odd ball carburator swaps to know what works well.

There are several reason I would opt for a flexable coupling like Jeff suggested.

1) The wire rope will eventually fatigue, while it may not happen over night it will eventually happen.

2) off idle (or electric equivilant) transiton will be no where near as smooth, it will cause a jerkyness just off idle.

3) return to idle (or 0 ohms in electric) more often then not it wont fully or properly return back to zero

4) to compensate you might need to put a heavier spring on the pot box which will result in premature wearing out of the shaft mechanism.

An over heavy return spring is a killer of throttle shafts in carbs I can't see the same action in a pot box responding any differently.

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Post by a4x4kiwi » Wed, 21 Jul 2010, 21:51

If I can chime in as well. Sorry guys, I know you put a lot of thought into this.

Is the pull on the throttle pot in line with the movement or is it on a slight angle. I ended up mounting my throttle cable and put on a separate piece of ali plate because I could not get a straight pull from any location in the engine bay.

If there is a molded 'barrel' on the end of the cable, you might be able to use that in one of the holes in the pot and make a spacer to hold the other end. See http://a4x4kiwi.blogspot.com/search?q=pot for a pic of mine.
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Post by EV2Go » Wed, 21 Jul 2010, 22:05

Mal I did a similar thing on Kearons pot box after he had a go at mounting it. It just wasn't returning properly, unlike yours that looks like it hooks over at the end, I just made up a second plate that was parallel to the pot box arm and with spacers at both ends used two small bolts to attach the second plate, worked a treat and returns perfect.

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Post by a4x4kiwi » Wed, 21 Jul 2010, 22:30

"I just made up a second plate that was parallel to the pot box arm and with spacers at both ends used two small bolts to attach the second plate, worked a treat and returns perfect."

Good description. This is what I did also.
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Post by EV2Go » Wed, 21 Jul 2010, 22:47

ahh ok form the picture I thought your arm looped around at the end. Also you appear to have the ball at one end, where as I put the ball between the bolts but same difference... stops the ball binding on the arm and allows a free return and that's the ultimate goal.

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Post by coulomb » Thu, 22 Jul 2010, 00:20

I made a less crude RS232 converter from a 74C04 hex inverter, using two inverters so I could get some positive feedback (hysteresis) using two resistors. [ Circuit appears a few posts below. ]

The output is crisp now, and I get sensible data. As expected, I get 12 bytes, the 4 address bytes and the 8 data bytes. I immediately realised that I had the bytes within the 16-bit integers swapped. Endianness! The oldest trick in the book!   Image

I coded up a quick swap bytes macro, reassembled, reflashed, and the charger ignores the packets just exactly as before. But at least now I know what the charger is expecting, or at least what the CAN box produces if I use an appropriate converter circuit.

Next I'll have another go at feeding this RS232 to the charger without the CAN box now that I'm more sure that I know what it wants.
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Post by Electrocycle » Thu, 22 Jul 2010, 01:07

that location for the potbox is also likely to get a bit wet during rain.
I'd put a cover over it for protection
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Post by 7circle » Thu, 22 Jul 2010, 04:21

Have you used the CAN box to start charging?

The charger may be expecting to be set to zero then set to the desired charging max voltage and max current.

When monitoring (Sniffing) the signals from the CAN box to the ElCON charger, do you only see one type of packet?

Does the Endianess going in match what is comming out of the charger?

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Post by coulomb » Thu, 22 Jul 2010, 05:35

7circle wrote: Have you used the CAN box to start charging?

No, that's what I'm trying to do.
The charger may be expecting to be set to zero then set to the desired charging max voltage and max current.

Really? Well, I guess it's worth a try.
When monitoring (Sniffing) the signals from the CAN box to the ElCON charger, do you only see one type of packet?

Yes. But that's probably because I only send it one type of CAN packet. I don't have an Elithion BMS to experiment with; that seems to be what it's expecting.
Does the Endianess going in match what is coming out of the charger?

Heh, good question. It didn't, but it does now.

From the charger:
18 ff 50 e5 00 0a 00 00 10 00 00 00

To the charger:
18 06 e5 f4 10 08 00 0a 00 00 00 00

These are pasted from logs. The 00 0a from the charger is saying that the actual voltage is 1.0 volts (10 tenths). The 00 0a to the charger is requesting 1.0 amps. The CAN IDs (first 4 bytes) are from the Elithion page.

It's been rattling around in my head that maybe the charger wants to see higher voltage at its input. My RS232 dongle puts out signals a little under 7 volts positive. I can see protection diodes at the charger input for below ground and above +12 V. So maybe it's expecting at least 2/3 of 12 V input, or around 8 V peak, and I'm only sending it less than 7 V. I might modify my dual inverter circuit to run off the 12 V of the charger, to see if feeding it rail to rail signals helps.

Of course, it's still a mystery to me how the CAN box is supposed to work with the charger, when there doesn't seem to be a pullup resistor. I thought I found it earlier today when I realised that there was a sixth resistor not on my circuit. There seemed to be intermittent conductivity from the CAN box to charger circuitry (R2) to R3. However, it is in the megohm region, and seems to be an artifact of the multimeter. It seems pretty clear that R3 has nothing to do with R2; it's just a smoothing resistor.
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Post by coulomb » Thu, 22 Jul 2010, 05:51

In case it is of use to someone, here is the circuit I used to convert the output from the CAN box (opto-transistor with 5k1 resistor in series) to my RS232 dongle:

Image

The 15k resistor is the lowest I can use to pull up the input as fast as possible, while still allowing the input to fall to below about 1/3 of the 5-6 V I get from the DTR signal, less a diode drop. The diode was an afterthought; I figured the chip wouldn't be impressed if the RS232 decided to disconnect and put -3V or so across it. The second inverter and 150k resistor add hysteresis to the circuit for noise immunity and crisp transitions.

Being a CMOS inverter, the output will be basically rail to rail. I would have used an operational amplifier if I could find one, but this circuit ended up with fewer components anyway. I guess the two inverters and resistors end up being a sort of Norton current amplifier. It seems to work well enough.

As mentioned earlier, I might try and drive the charger through a similar circuit running of the 12 V from the charger, so that it can't complain about the signals not being high enough in amplitude.

[Edit: DTR = Data Terminal Ready, a signal that is high when the PC is connected and ready to send data. It is commonly used as a small source of power; I use it for the inverter chip.]
Last edited by coulomb on Wed, 21 Jul 2010, 19:58, edited 1 time in total.
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