Here is an old black and white video explaining how a differential works in a rear drive car.
I found it very informative.
www.wimp.com/differentialsteering/
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Very good Videodoc, clear and simple.
I could never get my head round the reason that if you turned one of the driving wheels clockwise when they were off the ground the opposite wheel would turn counter-clock, I just knew it did. I once worked with a guy (an ex-trucker too) who was convinced that all vehicles used one wheel to drive forwards and the other to reverse because of this. What surprised me even more were the number of car-savvy colleagues who were nodding in agreement while the rest of us were rolling our eyes to Heaven.
Last edited by: Robin Regal on Sun 18 Dec 11 at 20:50
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>> I could never get my head round the reason that if you turned one of the driving wheels
>> clockwise when they were off the ground the opposite wheel would turn counter-clock, I
>> just knew it did.
Another of the benefits of a youth spent building and racing Tamiya R/C cars. Taught me the fundamentals of double wishbone suspension, trailing arm suspension, tracking adjustment, dampers, differentials, propshafts, drive shafts, universal joints and AWD systems. Not only did you have to assemble it all, but adjust and tweak it afterwards, plus repair it when you inevitably broke it through over-exuberance. :-)
If I ruled the world, these would be issued as part of the national curriculum in GCSE science classes.
Last edited by: DP on Sun 18 Dec 11 at 21:32
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>> Another of the benefits of a youth spent building and racing Tamiya R/C cars.
>>
Same here, I understood how the diff worked but could never get my head round the different rotation of the wheels. I have three Tamiya R/C cars on the shelf behind me (plus two Kyosho R/C bikes).
Maybe I'll strip one down and investigate.
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One way to imagine this, is to consider a child's see-saw.
As the hinge in the middle (assuming no friction in the bearings) cannot transmit any torque itself, the total bending moment on one side must always equal the bending moment from the other side.
When you push one side of the see-saw down, the other end goes up.
The planet bevel gear in the differential takes on the anagous role of the see-saw's bearing - the total torque acting on this gear must always be balanced, as the gear is free to turn on its bearing. The difference from the see-saw case is the bevel gear on the end of the half shaft turns the motion through 90 degrees.
Therefore, in analogy with the see-saw, it's to be expected that turning one wheel forwards means the other wheel goes backwards - just as one end of the see-saw goes up while the other end goes down.
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>> turning one wheel forwards
>> means the other wheel goes backwards - just as one end of the see-saw goes
>> up while the other end goes down.
>>
A local farmer once warned me of the dangers of a tractor getting out of control.
He said if you were going down a steep incline under engine braking, whatch out that both driving wheels were turning forwards. The moment you saw one turning backwards, it meant that the tractor was accelerating under gravity faster than one of the wheels could grip, and that the other gripping wheel was driving the wheel with lost adhesion backwards, through the differential.
At that point you have two options. If you are very brave, accelerate until both wheels have regained traction, then decelerate again. Otherwise, he said, that was the moment to jump off.
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Ah, Tamiya - the pioneers of acrylic model paints while the rest of the world clung to oil-based enamels. My model-building days were over before I properly discovered the difference, but now the 10yo Beestlet Major is kit-mad and wants to know if he can mix acrylics (which he started with) and enamels (which offer more colours) on the same model.
I'm sure VidDoc won't mind me asking DP for a little advice.
};---P
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I thought any fule kno that the diff is to allow the wheels to rotate at different speeds when moving from the slow lane to fast lane on the motorway. :)
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>> LSD anyone?
The thrust washers on the planet wheels are an interference fit - at least that's what some triallers have been accused of.
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You should have had a Meccano set or two..
I remember building a differential, ackerman steering and a gear box when I was 10. The Mamod steam engine came a year or so later.
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The Lego shop is just down the road from my office, and later today I'll be popping in to get the nipper his xmas pressies - electric motor and some of the technical linkages and stuff so he can make his own cars.
Also, WilDeBeest, I'm off to the model shop for a Curtis Hawk fighterplane. With the teeth.
Vicarious Xmas gifts for the win!
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I learnt how differential works from the Lego (It was pre-YouTube era). They had working differentials for a long time.
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Tried Tamiya R/C but progressed onto Mardave, made in Leicester i recall.
Where Mardave scored was that you could buy every single part individually by mail order at excellent prices, where parts for Tamiya and Kyosho were way over the top, the Japanese plastic stuff was also too fragile.
Interestingly Mardave's dampers you assembled from scratch and filled with oil of your choice, and via holed internal fittings vary the rate of damping that really worked, made for some fast rough ground racing without damage, where IMO the competition were weak, steel rods for suspension pivots and other stress points too.
I also recall they came with limited slip diffs which again you could finely adjust.
Based on a simple alumium plate chassis with front suspension sloping back, so obstacles hit the suspension absorbed most of the shock and the car went up and over, good simple designs that the taught the kids (and me the biggest kid) a lot.
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>>>Interestingly Mardave's dampers you assembled from scratch and filled with oil of your >>>>choice, and via holed internal fittings vary the rate of damping that really worked
That's how most r/c cars do it.
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>> That's how most r/c cars do it.
>>
Maybe now, i haven't bought a Japanese one for at least 20 years, not sure it was the case then though, maybe on some models....a Kyosho i bought for one of my brood was very disappointing as its dampers were all show and it could make no decent progress through constant bounce.
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brilliant video....have a look at the next but one in the series....the russian near miss
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How a differential works - Robin O'Reliant
