3 or 4-gear?
 

Just out of curiosity, which are the advantages and disadvantages of both 3-gear and 4-gear systems? And is there any other way that might be leading to the holy grail?:lol:

when your on throttle the rotational mass of the armature throws the car’s weight forward onto the front wheels with 3 gear where as 4 Gear turns the motor around so the armature throws the car’s weight back onto the rear wheels so with 3 gear you have more steering but less grip rear end on steering where as with 4 gear you have more rear end grip on throttle but slightly less steering which is over all better as abit of setup change can give you more steering

Nearly ..... depends on which way the motor is facing.

With a convensional 2wd a 3 gear places the motor so the pinion shaft is on the right hand side (viewed from above ... front away from you) so the rotation of the armature helps aid traction as Mike says.

In a mid mounted 2wd a 3 gear reverses this and so the 4 gear transmission is used to correct for this.

There have been belt driven 2wds (Schumacher and Kyosho) but to be honest there is was little too much drag in them compared to the free running gear trains.

I think that there is nothing revolutionary that can happen to 2wds with transverse mounted motors.

im not sure your right Roger.

in mid-motor cars the motor still runs 'forwards' and if its go 3 gears in a traditional gearbox setup the kick of the motor will always kick the weight towards the front of the car in a B4 or an X-6

the pinion/spur for 3-gear trans that are done 'right' and not just a home-made-job have the spur/pinion on the right side of the car.

the 4-gear boxes have the spur/pinion on the left and the kick is reversed.

Chis is spot on. As per usual ;)

I think Roger might be confusing some of the DIY conversions which have been done which actually just spin the gearbox around, this means you need to effectively run the motor in reverse to make the car go forward.

Either that or his explinasion is confusing :confused::D

Mike explains the "effect" of the two types very well.

even the DIY cars, the motor ended up kicking the same way on a 3-gear car because you had to run it backwards

I'm sorry for interrupting guys, but here is another question :lol:
Suppose you have 2wd buggy, which you want to convert to a mid-motor one. Do you think it is possible to have the motor in an other direction (like B44) with endbell pointed forward? With this I mean with the motor as central as possible, maybe even perfectly centered. And would the movement of the motor have any (negative) effect on the car's handling?

Torque reaction/steer? Not so good for making changes in the air

So not advisable for a 2wd car? Too bad, as the weight would be positioned very central.

Something like this ? ;)

http://www.gforceimages.net/atomic-c...lim2_specB.jpg

:eh?: thats the one me and matt were thinking of getting a little while ago

There was another version below, but the spec B was the best, only thing stopping me developing the Spec B at the time was the lack of a decent slipper clutch. It was very nicely balanced and drove like a 4wd.

But now the B44 slipper is out, which is a lot more adjustable ;) who knows lol.

http://www.gforceimages.net/atomic-c...lim2_specA.jpg

Yes, but with the motor further backwards, without the center CVD bone, so against the gear box like the S2 and X-6, but faced in another direction.

I would have thought that the armature shaft position relative to the wheel axle would play a part too .... maybe wrong ... will think about it some more.



Ok ..... never seen a 3 gear mid-mounted 2wd with the motor mounted with the so the pinion shaft is on the "conventional" side ..... then I was racing gas for nearly 3 years so may have missed them!

I believe in the home made section of oople someone has done this using a ZX-5 gearbox and rear end, looked quite good.

No, the position of the motor relative to the rear axle doesn't matter when considering the weight transfer effects of the motor's rotational inertia. I was surprised when I worked it out, too.

<physics>
Here's my understanding/reasoning: The torque the motor exerts on the driveline has to be counteracted by an equal and opposite torque from the chassis, otherwise the motor would just spin in the car and never turn the driveline. Where does the chassis' torque come from? The ground - it loads up some wheels more than others, which is what we call weight transfer. So, how does the motor's position play into this interaction? Well, torques act over distances (Torque = Force x radius). Obviously, the effective distance between the motor and the chassis (I'll just call it the chassis instead of getting into center of mass and etc) is the same as the from the chassis to the motor. Since the two torques mentioned earlier have to be equal (thanks Newton!), the length terms drop out of the equation. So anywhere the motor is on the chassis - behind the rear axle, mid, up front, anywhere - the weight transfer effect is going to be the same. Changing the motor's direction simply changes the direction of the weight transfer, not its magnitude.
</physics>

Hope that all makes sense.

:woot:

Motor... driveline... you're probably right. And maybe somewhere along the driveline, anti-squat will come in and play.
But I think this entire 3-versus-4-gear business isn't about drive train torque, that's the same in any case. I think it's about the rotational inertia of the armature ... ... and pinion. Because they spin so much faster, their combined inertia is much bigger than the inertia of spur, slipper, diff,... the only other factor big enough to be significant being tyres. (tires to you, Paul ;) ) Anyway, yeah, inertia. The thing that makes a motor jump out of your hand when you hit full throttle holding it, that 'kick'. I think it does matter *where* the kick happens. The closer to the rear axle, the bigger the (instantaneous) weight transfer.
I think this is the reason the XX4 flies the way it does, with the motor spinning 'the wrong way' (IMHO) but being way forward.



***Disclaimer*** Been a long day, brain in neutral, fingers in gear.

Paul your physics are sound with regard to torque couples.

I am however in agreement with Elvo that position on the fast rotating mass of the armature assembly .... particularly when there are large near instantaneous changes in it's speed of rotation.

Again, with Elvo ...... late, heavy day and not exactly firing on all cylinders ... was early when I made my first post.
As I say ... going to have to think about it some more.

Agreed; the motor and tires (tyres to you, Elvo ;) :lol:) play the primary roles in the rotational-inertia game, and driveline can be practically discounted. We can even conclude that the tires play a larger role than the motor; if the armature's effect was larger than a "normal" motor-direction car would react oppositely to throttle changes in the air to what they do now - braking would lift the nose, and acceleration would drop it.

Anyways, I guess being a typical physicist I was singling out only the change in motor direction, and theoretically considering everything else on the car to be exactly the same. Further, I was only looking at the magnitude and direction of the torque generated in the chassis. In that case, the effect of flipping the motor would be the same no matter where it was located. The more practical things you guys are talking about - weight distribution, suspension settings, we could get into chassis flex if you wanted - I agree, those will affect how this "chassis torque" is realized as weight transfer, and thus how it is felt by the driver. Testing whether motor placement made a difference could be difficult, I think; you'd have to have two different cars (different motor placements) each with two different transmissions to reverse directions; however the cars couldn't vary much in terms of stiffness, weight distribution, suspension, etc, so that the motor position was the primary variable.

Fun Discussion! :thumbsup:

You, Elvo and I will probably find this an interesting debate ..... I think most others will be asleep by the end of the next page ..... LOL

By the way I've finally got around to driving an X6 and I must say well done, quite a car!
The one I drove was a 4 gear but with a "less than perfect" set-up on it (sure the owner won't mind me saying that) but the potential was definately obvious. It wasn't quite as quick around a lap as my RB5 but then again a bit of set-up help for the regulalr owner / driver will no doubt get it there.
You can tell a car that has potential straight off, no matter how far off the set-up, just as easily as you can a car that is always going to be rubbish!

I think I'm going to side with Elvo and Roger (!) in that the position of the motor in the car does change the magnitude of the weight transfer.

Bear with me here as I might not use exactly the correct terms as I don't study/work in engineering...

The force the motor exerts on the chassis on acceleration/deceleration is a twisting force, trying to alter the pitch of the chassis, which pivots at the rear tires. If you think about it the closer the motor is the the diff the more pronounced the effect will be. Imagine if you had a car with the motor a foot further back than normal, but it magically had normal weight distribution and pitch inertia, is it going to want to wheelie more or less than normal?


Back to the 3/4 gear question... I'm not a big fan of 4 gear cars, the drawbacks outweigh the benefits IMO. The good bit is you get a lot more forward drive, but the bad bit is... you get more drive :eh?: Every 4 gear I've driven has had almost no on-power steering, and had quite bad lift-off oversteer as the weight is thrown forward and backward again. I'd rather have the consistency of a 3 gear car and change the overall balance as needed :)

There are two "force-relationship-things" going on here, and I don't think I was clear enough in my posts above distinguishing between them. First, there's the relation between the motor's torque and the reaction torque in the chassis. Then, there's how that reaction torque is realized as weight transfer between the chassis and the ground. The first of these has nothing to do with the location of the motor relative to the chassis (as long as they're rigidly connected), and I can prove it to you. The second is affected by weight distribution, suspension set-up, and everything else, and its this second part that most drivers are more familiar with, I think.

The first of these relationships, between the motor and the chassis, is independent of the motor's location in the car as I laid out in my first post. More simply: on any acceleration, the motor exerts a torque, or twisting force on the car. The motor and the car are rigidly connected; since the motor can't twist in the car the car has to exert an equal and opposite torque on the motor. Since these are equal and opposite, the length between them cancels out of the equation - the length term doesn't matter. The torque interactions between the car and the chassis - including whatever effect changing the motor's direction has - are constant no matter where the motor is located.

The second interaction, or torque-relationship, or whatever you want to call it, occurs between the chassis and the ground. If there is no ground, the chassis' torque is realized as rotation - the "gyro effect". On the ground though, we have a similar situation to the above, this time the car exerts torque on the ground and the ground "pushes" back. The difference here is that the two are not rigidly connected - there's suspension, tires, etc. between them. Because they can move relative to each other, moments of inertia (essentially the weight distribution, including where the motor is), spring rates, suspension settings, and all that other stuff become important.

So... the location of the motor does not affect the magnitude of the torque between the motor and the chassis. It does, however, affect how this torque is realized through the suspension and in the way the car drives.

Whew. That's been about an hour or so, but I'm confident about it - I hope it makes sense. Time for bed.

Oh, and Roger, thanks for the kind comments! Very much appreciated, glad you liked it.

Not on mine it doesn't!!! It's so safe it's unreal. You need to try a good one Rich and then you will really know, I know you have tried a few but it is all down to the set up and what we came up with this winter is very good.

E.

On my 'home brew' mid motor B4 thingy I tried 3 gear (without having to reverse motor direction) and 4 gear. Of the two I prefered the 3 gear for the reasons Rich has stated, and we have chatted about it in the past.

The last time I drove an X-6 it was a 3 gear, now I have returned I am driving a 4 gear. I have to say it feels very much as I remember, I'm not sure why the X-6 is less affected by the change (well I have a few ideas), but if I'm honest I don't care. The car is good and I'm just going to get on with driving it now........

........ or trying to fit a 5 link rear end! :woot:

G

Sorry Paul, I didn't realise you wer talking about two different things there, I was thinking of them both as one if that makes sense :)

The X6 is about the only mid-motor 2wd I havn't had a chance to try properly, anyone with a spare car they don't need for a bit? :woot:

I have only skim read through the recent posts,

but I would have thought that the motor kick effect would be more pronounced if the motor was mounted at (or as close to) the cars CoG and it it was a way forward or backwards from that point

Agreed Chris, i was on the understanding that if the motor is centrally mounted then it will make the chassis pitch more when on or off power. if it is 80% to the rear it will transfer more weight to the rear end on power but less to the front off power, possibly 30% less?:lol:

Maybe my way of thinking is wrong??:confused:

my theory is that its easier to apply the torque force at the 'pivot' (which the CoG will be most like the pivot when in the air) than trying to twist something that is off centre to the pivot to turn the pivot

note - not 'lever' something, 'twist' the handle the apply the force

hope that makes sense - :eh?:

Erm... basic free-body-diagram theory here. A moment is a moment is a moment (or torque, or couple, as you prefer). It has exactly the same effect no matter where it is applied - the reaction moment arm, for this discussion, is the distance between the front tyres (where the reaction force is reduced) and the rear tyres (where it is increased by an equal amount) - i.e., the wheelbase - which doesn't change.

The only influence that the position of the motor has is on weight distribution and moments of inertia.

If you could build a car with two motor mounts, one in front and one behind, and you could fit a motor in both positions but only fit a pinion to one of them, then it wouldn't matter which one was spinning.