Weber and Coulomb's MX-5

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Post by coulomb » Sun, 05 Apr 2009, 03:35

We weighed the car at 662 kg, so half of that is 331 kg. (It's missing engine, gearbox, bonnet, boot lid, PPF, prop shaft, radiator, fuel system, soft top, etc).

Also, a lot of the weight is transferred to the two wheels on the ground; in the limit if the car was on its side, there would be no force needed to hold it up (all of the centre of mass would pass through the side).

Also, the engine lifter was still there taking a fair bit of the weight. I agree it isn't ideal; if we do this more often, we'd better think of a better prop.
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Post by acmotor » Sun, 05 Apr 2009, 03:38

Ummmm, with vehicle at that angle it is nearly balanced so ladder would be fine. Actually, there is more risk of it going right over !!

Nice pics coulomb. Image
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Post by weber » Sun, 05 Apr 2009, 04:15

woody wrote: Rotisserie style is good :-)
Using a ladder as a safety under a car is probably not up to your usual standards though. 1/2 a car : 500kg whereas a ladder normally says 120kg is too heavy. Ignoring that the car will be moving already when it crushes the ladder like a coke can...


It would not be moving when it hit the ladder because it was already _on_ the ladder. This is obscured in the photos. We lowered it so it was partly resting on the ladder and partly on the webbing straps and crane. We did this so
(a) there was no possibility of the ladder being knocked out of position, and
(b) because those webbing straps are alarmingly elastic!
It doesn't inspire confidence when you bump it and it bounces! Even though they have a breaking strain of 900 kg and we're using two of them.

Yes. Don't try this at home kiddies. This was meant to just be a trial run and we will definitely do it better next time, but we couldn't resist getting a bit of work done in the last hour that was left in the day, before lowering it until next Thursday. We work on the project on Thursdays and Saturdays (and some Sundays).

As you says, we start off lifting half the car's weight, but because the center of gravity is above the wheels, by the time you get it up to 45 degrees like that, most of the weight is on the two wheels on the ground. I'd estimate we only had 1/3 of the weight (about 200 kg) on the combination of the ladder and the crane-with-webbing-straps.

We could lift it higher (maybe 60 degrees) if we had higher props. It was in no danger of tipping the other way at 45 degrees. Next time we will have two props under it, one at each end. Ladders are damn convenient for the job. Can anyone suggest something better that wouldn't require a great deal of work.
Last edited by weber on Sat, 04 Apr 2009, 17:18, edited 1 time in total.
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Post by Electrocycle » Sun, 05 Apr 2009, 15:58

years ago I was doing a lot of work on the floorpan of a car, and I ended up using two engine cranes to lift the whole car up on its side, then sat it on tyres (it was a bit more dismantled than the MX5 though)
I used some timber props from the car to the garage walls to make it really stable.
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Post by coulomb » Mon, 06 Apr 2009, 14:15

We decided to tilt the MX-5 on its right wheels yesterday, and use the more expensive, wide yellow tie downs. These have a breaking strength of over 4 tonnes:

Image    Image

The wider tie-down doesn't fit so well into the hook, so we cut a hole in some hardwood with a 32mm (Edit: was 25mm; need inside diameter) hole saw, keeping the cylindrical part, cut that in half, and filed a groove around the outside (so it holds in the hook better). That seemed to considerably reduce the stress on the strap in the hook.

Image   Image   Image

Edit: last photo. This is actually the spare; the real one is under a lot of tape. You can't see the groove very well; it would go around the outside semi-circumference of the circle.
Edit 2: attempted to fix the yellow line.
Last edited by coulomb on Mon, 06 Apr 2009, 19:48, edited 1 time in total.
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Post by woody » Mon, 06 Apr 2009, 15:55

coulomb wrote: Image
How heavy is the ladder now?
coulomb wrote: Image
Ah, the EV Maniacal Grin
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Post by weber » Mon, 06 Apr 2009, 15:58

The 4300 kg strap was only $60 from SuperCheap Auto. It's probably way overkill but it sure "feels" safer. I know logically that if you have a nylon webbing strap and a steel rope with the same strength, the nylon will elongate about 6 times more than the steel under the same strain, and that that's OK. But viscerally I just can't accept it. So now we have a nylon strap that has 6 times the rating of the crane holding it up!

Of course we could have used steel rope, except for the little problem of the creases it would make in the doors at the start of the lift.

We took woody's point seriously and actually measured the force on the ladder, by our usual method of multiple bathroom scales. In this case, one under each foot of the ladder, as you can see in the photo above. This tilted the vehicle a little more (to a full 45 degrees), so it isn't an accurate measurement of what the force was without the scales under.

We slowly lowered the crane, watching the four scales and stopping to nudge any foot that was getting more than its fair share of the load. (This may be a good reason to always have the scales there). The total levelled off at 114 kg. So it was better than I estimated yesterday, and acmotor was right. We would not want to tilt the MX-5 much further or it would be too easy for someone to trip and fall against it, or for some visiting moron to show off by lifting it, and make it topple the other way. Never underestimate the moron factor. See crazy-man in above photo. Image

I'm guessing that in its life as a ladder it has to take almost the full rated 120 kg on one leg at times, although it would be interesting to read the actual AS/NZS standard. Even so, after measuring the force we cranked the crane back up until there was only 60 kg on the ladder. Two identical 150 kg ladders would be ideal.

The photo below shows the detail of how the car rests on the ladder.

Image

I should point out that the reason we did this car tilting business is not to show how clever we are. OK, not merely to show how clever we are, Image but to let us cut away certain parts that can only be cut from underneath, without having to work in a cramped space with an angle grinder above our head! These things include exhaust system hangers and the brackets the fuel tank was mounted on, all of which project into potential battery space.

Even with a proper vehicle lift we would still have had to use the angle grinder overhead. Angle grinders are dreadfully dangerous things as it is. Tilting so we can work in front of us seems far safer.

[Edit: Included photo after uploads started working again for no apparent reason.]
Last edited by weber on Mon, 06 Apr 2009, 06:47, edited 1 time in total.
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Post by Johny » Mon, 06 Apr 2009, 16:14

weber wrote:I was going to include a photo showing the detail of how the car rests on the ladder, but when I click the "Image upload" button I get "insufficient permission, access denied". Can anyone tell me how to get that fixed?
Check in your "Members Control Panel" that you have any space left. It just might be too many big pics.

Edit: Worded betterer
Last edited by Johny on Mon, 06 Apr 2009, 06:15, edited 1 time in total.

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Post by weber » Mon, 06 Apr 2009, 17:32

Thanks Johny. It wasn't file space. But when I went to the control panel I found the upload there worked so I went back and edited the post and it worked there too. So you can see the ladder detail there now.

Here's a good angle-grinder safety checklist from the WA government:

http://www.safetyline.wa.gov.au/pagebin ... zd0006.htm
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Post by coulomb » Mon, 06 Apr 2009, 17:38

Excuse my ignorance... what's a drop saw?
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Post by acmotor » Mon, 06 Apr 2009, 17:46

I know you guys are soooo busy on the conversion that we have to do your google work for you ! Image



Image
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Post by coulomb » Mon, 06 Apr 2009, 21:28

Duh, of course. I just didn't connect that with cutting metal out of a vehicle. I have trouble getting a 102mm disc in there; such a monstrosity would never fit.
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Post by EV2Go » Mon, 06 Apr 2009, 22:11

coulomb wrote: Duh, of course. I just didn't connect that with cutting metal out of a vehicle. I have trouble getting a 102mm disc in there; such a monstrosity would never fit.


I'm lost... you wouldn't ever use a drop saw to cut a piece out of the boot it is designed to be used on solid surface like the floor or a bench.

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Post by weber » Mon, 06 Apr 2009, 23:29

Here we were, thinking the owner of that white MX-5 above was a bit naughty, cutting into a cross-member. Andrew Schwarz was doing the right thing, even leaving the spot-welding flanges beside the rails and cross members. Then he invited his mate "Dave" over to help, and Dave just cut them all away and whacked out the whole cross-member!

            Before Dave.      (Click to enlarge)     After Dave.

Image    Image

<Gulp> ... I've seen grown MX-5's gnaw their own wheels off rather than talk to "Dave". We sure won't be letting "Dave" anywhere near our MX-5. Image
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Post by weber » Mon, 06 Apr 2009, 23:44

EV2Go wrote:I'm lost... you wouldn't ever use a drop saw to cut a piece out of the boot it is designed to be used on solid surface like the floor or a bench.

Quite right. Coulomb read the safety brochure I posted on angle-grinders and saw that the overriding consideration is not to use them with cutting disks (as opposed to grinding) if there's any other option (because they are so bloody dangerous).

There is in fact an alternative for car body work, even in quite tight spaces. The sabre saw. It produces a far cleaner cut too. Here's one being used by Andrew Schwartz on his Miata (MX-5), before "Dave" got hold of it.

Image

(Click to enlarge)
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Post by juk » Mon, 06 Apr 2009, 23:47

Might as well bolt an outboard to the back of Andrew's; it might as well look like a boat if it's going to handle like one.

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Post by coulomb » Tue, 07 Apr 2009, 00:07

EV2Go wrote:I'm lost... you wouldn't ever use a drop saw to cut a piece out of the boot

Well, exactly. It's just that the West Australian Government article linked by Weber above said that angle grinders should never be used for cutting, always use a special purpose cutting tool like a drop saw.

I guess they weren't thinking EV conversions when they were writing that page...
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Post by woody » Tue, 07 Apr 2009, 05:22

Nibbler? Gas Axe? Hacksaw? Acid? Thermite? :-)
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Post by EV2Go » Tue, 07 Apr 2009, 14:41

coulomb wrote:
EV2Go wrote:I'm lost... you wouldn't ever use a drop saw to cut a piece out of the boot

Well, exactly. It's just that the West Australian Government article linked by Weber above said that angle grinders should never be used for cutting, always use a special purpose cutting tool like a drop saw.

I guess they weren't thinking EV conversions when they were writing that page...


Nah that’s crap I could cut delicate ice sculptures with an 4” angle grinder, it’s not the tool, it’s the tool behind the tool where it all goes wrong...

Some people have absolutely no forethought when it comes to cutting things. Things like brake lines behind the panel they are trying to cut, or the effects of the heat the put into the metal that is in close proximity of plastic and other easily melted items, little matter of fires you might start etc.

Angle grinders are as safe as houses if treated with the proper respect they deserve.

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Post by weber » Tue, 07 Apr 2009, 16:25

It turns out that "Dave" wasn't such a bad guy after all. He didn't cut off the spot-welded flages as I had thought, but bent them upward. And he at least partly replaced the cut-out cross-member with a piece of angle welded in further back. You can see these things in this photo.

Image
(Click to enlarge)

We'll run this by our engineer.

But yes, what a boat. All that lead above and behind the back axle. I can hear the poor MX-5 groaning in pain. We should only have about half that weight at the back, with the LFPs.
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Post by acmotor » Tue, 07 Apr 2009, 16:35

I do second that EV2Go. Image
Common sense, experience and operator skill prevail.

You can see the safety people have a big task though.

For instance a cutting disc (thin, parallel sided) should never be used for side load grinding, it is not built for it and side wear removes the reinforcing webbing and wheel thickness resulting in failure.
A grinding disk is more tollerant, although should only be loaded on the edge or face, never the back. Any wheel damaged in a drop or a jamb resulting in twisting should be replaced and the old wheel broken to prevent accidental re-use.
You can cut with either wheel but only clean up edges with a grinding wheel.
A grinding wheel produces a wider, hotter cut than a cutting wheel.
(and is using more mechanical/electrical power)
(Ummm, most angle grinders are AC/DC universal motors and would run off the EV battery pack !)

Then there are the different grades and compounds of disc abrasives suitable for Ali, steel, ceramics, masonary, plastics and so on in both cutting and grinding format for angle grinders. My fav. is the diamond disk I use on bathroom tiles. Cool, clean cuts like butter.

How did all that get started ? Oh,I remember, safety boots ! Image

Nice red weber ! Image
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Post by weber » Tue, 07 Apr 2009, 17:01

acmotor wrote:Nice red weber ! Image

If you mean the painted battery racks in the above images, those are not ours. We're not that far along yet. They belong to Andrew Schwarz's MX-5 in the US.
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Post by acmotor » Tue, 07 Apr 2009, 17:10

... and there I thought you had been onto photo shop. Image

Ok, that's good, cause I would not pass the welded angle iron that runs between the "chassis" rails. It will suffer fatigue failure as it pretends to control the chassis dynamics. (particularly with a hundred kg of cells on it).
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Post by weber » Tue, 07 Apr 2009, 18:12

ACmotor, there is a very substantial subframe bolted under those rails, hidden by the newspaper. You can see it in this picture.

Image     (Click to enlarge)

So it may not be as bad as you thought in regard to suspension dynamics. But I still tend to agree with you.

In regard to tools. It's nonsense to say it's only the user that makes it dangerous. Even the best of us sometimes make mistakes, have a bad day, get distracted momentarily, make a wrong judgment. Angle grinders are more dangerous than many other tools because they are fairly unforgiving of such mistakes. Google "angle grinder accidents" if you have a strong stomach.
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Post by coulomb » Tue, 07 Apr 2009, 18:50

acmotor wrote:Ok, that's good, cause I would not pass the welded angle iron that runs between the "chassis" rails. It will suffer fatigue failure as it pretends to control the chassis dynamics. (particularly with a hundred kg of cells on it).

Is that basically because it will deflect so far, having relatively low cross section compared to its length? Plus, boxes are (presumably) stiffer and stronger than L shapes of the same cross sectional area?

I'm guessing that an actual battery box with a steel floor could be as strong as the original... would you agree? I must have done exercises like this at Uni, but that was a few years ago now.
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