Be Excellent To Each Other

Nice. It really is a totally fucked up place when you think about it.

Wild West Gypsies.

Your GP can probably help with that.

Right, here we go. Shell has arrived, and I have just finished rebuilding the chassis. I amused myself by forgetting to put a pressure plate in the rear diff assembly and only realising when the build was 75% done, requiring the whole thing to be taken to chuffing pieces again.



HMMVW tyres, on Subaru rims. May need to get some new rims, methinks, as I'm not a chav. Need to come up with a colour scheme next.

Why is there a sheep on your desk?

It's the ram he removed from his laptop.

Black, obv.

That's looks aces, I am more than a little jealous.

Grim... can't you make your Tomcat radio controlled.. that would be awesome

It would, but 'probably not'.

The trim was going to be black. I was thinking traditional yellow, or maybe purple. Or, I don't know. Lime green's in this year.

This is completely different from building aeroplanes, mainly because with cars I wish I knew what all the bits actually did. When cleaning and reassembling all the geary bits (GEARY BITS) I couldn't for the life of me work out what it was all for. What the fuck *is* a differential?
I was just following the instructions with blind faith and assuming the man who wrote them knew what he was on about, whilst understanding nothing. This must be what it's like to be a fundamentalist Muslim.

The sheep is because there are farm animals all over every room of the house, thanks to First Born and his farming obsession. Hence the giant tractor in the background. I'm going to get him an RC tractor next year, when he's old enough to work it.

It allows the drive to be sent to the wheel with the least amount of resistance and allows the wheels to rotate at different speeds. If it didn't, when a car turned a corner it would scrub its tyres as the inside tyres would try and turn slower than the outside ones.

Ah, thanks. Um, how does it do that, then? Is there something magic in the size and alignment of the three cog bits?

Yes, basically. Have a read of this, it's quite good: http://www.howstuffworks.com/differential.htm

If you really want your head fucked with, I can explain how an automatic gearbox works

[edit]Start here, actually: http://auto.howstuffworks.com/differential2.htm

That's easy... An automatic gearbox works the same as a normal gearbox except it changes gears automatically.

Next please!!

PH34R

Does that explain how LSDs work, especially pure-mechanical ones? Because trying to figure that out really twists my melon, man.

It amazes me, stuff like that. I mean how the fuck did someone go about dreaming up something like differential gearing?

Nah, that's all chemical.

LSDs

They took a bunch of psychedelic drugs.

edit: GAH

Yup. They're quite simple, to be honest.

People weren't dumb in the olden days, man.

I couldn't bring myself to believe it was clutches, because clutches wear out.

I assume the one in my M3 is clutch-type, but it can transfer 25% power to the other wheel, which the description of clutch-type doesn't cover? Or is that the manual over-simplifying?

Only just barely. Factory clutches can cover well over 100,000 miles these days, and often are replaced not because they are worn out but because some oil has found its way onto the clutch plate and contaminated it (or so says my father, a truck brake engineer for Arvin Meritor). And that's a clutch plate that engages and disengages constantly as you change gear -- an LSD clutch only slips under hard cornering, when the diff is re-engaging, and that's not very often.

http://www.canadiandriver.com/2001/12/1 ... l-lock.htm looks interesting. Seems to be the model after your car.

That's probably the speed difference it needs before the clutch comes in.

VW had a system called "synchro" which was some sort of fluid which changed viscosity as it heated up by the slipping action.

edit: there you go http://www.syncro.org/VCTest.html
It looks like a very similar thing to the BMW diff mentioned, not surprisingly.

My transit has "traction assist" which actually applies the brake on the side that's slipping, using the ABS pump. This can help a lot in mud and snow.

That's a viscous coupling. My Range Rover has one of those, too. You have to make sure you use them or they go solid.


Yeah, that's the Land Rover system. Ford swapped it for a transit engine, which goes into all the new Defenders.

It uses the ABS sensor too, I think. I've never thought about it before but I see how this works now -- by locking the wheel with the brake, it gives the diff something to push against so it'll lock and allow you to get some torque down to the good wheel.

Not about locking, it's just to stop that wheel from spinning freely. If you've got RWD cars stuck in snow much (back when it used to snow), you might have done this trick manually by putting the handbrake on - this gives both wheels at least some load so there's a better chance of them both turning.

Yeah, but they do saywhich is mine. So when the wheels are rotating 25% different rates, the diff dumps torque to the grippier side?

When one wheel is spinning at 25% the speed of the other side, I think.

Hrm, I thought it referred to the maximum amount of coupling that can occur: i.e. 100% = wheels fully locked together / 0% = wheels not locked together at all, like a normal diff.

The amount of coupling within that range is controlled by the input driveshaft torque rather than the amount of slipping going on, traditionally anyway. So they aren't very useful on ice.

Confusingly, open diffs always push the same amount of force through each wheel. It's just that if one wheel is in the air (or on some ice) you won't have enough power going to either wheel to move forward, one due to traction, one due to the force applied. That's why putting the handbrake on can help.

It's a huge issue for off roading as you can imagine, and for the life of me I don't understand why there's never been a Land Rover off the production line with lockable front or rear diffs. I use an air powered locking mechanism for mine, that jams the pinion gear into the ring gear and forces everything to turn at the same speed.

Some automatic lockers (like Detriot Lockers) won't allow the driven wheel to be the fastest wheel, so it can still go around corners (by powering the slower wheel) but it shouldn't have traction issues.

Wow, you guys have sucked ALL the joy out of this one.

Sorry Zarzie.

I still love you all. I just thought you should know that there's a little less magic in the world.

All I know is: it's fucking terrifying when I'm going round a corner under power and the less-loaded wheel hits a slippy patch. The sideways jolt is, well, bowels-jolting.

Sorry Z. If it helps, try to imagine a fat Schumacher look-a-like browning his pants, and that's what the above probably looks like.

My new toy:

Tiny Airfix kit-sized aerobatic plane. Four channels, all fully proportional:

Needs a lot of controls.

Yes, it takes three people to fly it.

How much?

Even a little bit.

It's only a little plane.

£60 including everything but a transmitter. I already have one but they need to be the same make because since RC gear has begun moving to 2.4GHz there are only proprietary protocols so unlike with 35MHz you can't mix and match between manufacturers. But on the plus side the link is just so much better.

I wondered why I couldn't use my 4 channel GWS transmitter to talk to my 15 year old Tamiya rig Wildcat*.

*More photos this week!!!1!!!!11!!

Anyone got any bright ideas on how to make dummy headlight lenses?

Soak a contact lens in superglue?

How big do they need to be?

Er, about the size of a one pence piece. Or slightly smaller. Maybe a 5p.
I also want to make fake tail lights, indicators and so on. As per real Wildcat.

That was my initial thought. Hooray! We're probably both idiots.