Torque question

[PorkyMonster]

 

On 5/28/2017 at 10:10 PM, PKW said:

i agre with what is there, and yes my mechanism lead to a permanent differential "work" but the results is that torque is not distributed equally to both axles and so you have "kind of more torque" to the front one, this is why it slips and the other stall because the dill gives more torque to that one.

Yes, geared differently, opposing sides of the same differential will end up with different rpm and torque. However, I suspect that this difference only exist when one of the sides cannot overcome the road friction. So when both sides managed to overcome road friction and the car moves in a straight line, the differential will balance them out and, in the course of doing so, incur lots of overhead (of course, we all know that. That's also what my experiment tried to confirm.).

 

16 hours ago, Didumos69 said:

Thanks for your experiment! Your observations may have to do with the following effect: When a diff needs to 'work' (has one output axle rotating faster than the other) under torque, the bevel gears inside the diff will push each-other against the diff housing, which will in turn cause friction. This would mean the diff isn't really open.

Agreed. This is also apparent when I lift up one axle and hitting the controller (effectively freezing the axle on the ground) - the difference in feeling of the initial torque (1) when axle with gear down is lifted, compared to (2) when axle with gear up is lifted. Shows that there is (a) friction within the differential which caused a delay in its ability to channel all torque to the lifted axle, and that there is also (b) torque difference due to the asymmetrical gearing.

 

13 hours ago, Lucullus said:

According to manufacturers of cars with unsymetrical torque distribution, its main purpose is increasing the vehicles balance while cornering/corner exit. Therefore I think its hardly possible to observe any difference in performance of a lego car equipped with it (even if someone would be able to create a flawless lego representaion of the real system). PF and even buggy motors seem to be not powerfull enough to use such a systems potential. But if someones goal is to create a detailed representation of a vehicles drivetrain it might be worth to think about it.

You're right. And indeed, PF and buggy motors won't be powerful enough for anybody to see any difference in performance between with and without realistic torque vectoring mechanism. IMO, such mechanism must not impact on the vehicle's normal, straight line, performance... so a simple Lego differential, geared differently at different outputs (as shown in my experiment), won't serve the purpose. We'll probably have to step into the realm of electronics to override some of the default behaviors of an open differential to truly model vehicles with such feature realistically.

 

On 5/24/2017 at 2:35 AM, tomek9210 said:

Let's say I would like to implement torque vectoring to the drivetrain - more torque to the rear wheels and less torque to the front ones. Am I correct that I should gear down the axle coming out from the center differential to the rear axle and gear up the axle to the front axle? Won't the wheels slip because of different rotational speed?

On 5/27/2017 at 9:28 PM, tomek9210 said:

Look here at Madoca's Pickup. There is a reduction in rear hubs, meaning that rear wheels get more torque than front wheels and their rotational speed is lower than front ones'. Is it compensated by the central diff? As we can see in the video, the model drives well, no slip occurs.

As shown in both @PKW and my little experiment, there won't be slippage when all wheels are able to overcome contact friction with the road, because the central differential balanced out all rpm differences. However, my experiment also showed that there will be overall performance (both speed and torque) impact when traveling straight on flat surface.

Too bad Madoca did not compare the performance of that pickup with one without the gearing down at the rear hubs...

[TeamThrifty]

Hi, old thread but this was something i was thinking of and had a similar idea with regard to the output ratio's from each side of the central diff... interesting reading and i agree, it wouldn't work. Related reading on how Audi did it - a torsen central diff automatically varies the torque to front/rear axles... and you can get 3d printed lego torsen diff's. Now that has got me thinking for my pikes peak Peugeot moc...