Need Help Making Heavy AWD SUV Move Better

[StudRobotics]

I'm back with one last issue in my GX EV3 build. I just got done finishing the doors, side panels, rear trunk door, hood, and some part of the roof. But the vehicle was so heavy that when I drove it around, it kept on doing the same thing. The diffs were clicking and the car had very much difficulty moving.

Here is a picture of the bottom of the vehicle.

Most of the clicking seems to be coming from the rear diff when I move the wheels by hand. I can either do two things.

1. Reinforce the rear diff somehow.

2. Improve it's off-road performance and stop the clicking somewhat by replacing the diffs with knob gears. But this will come at the cost of independent moving between the wheels.

What should I do? Please give me the best response you can so the clicking will stop and I could finally take this AWD machine through some rough terrain like a real SUV. I really appreciate any advice.

[Void_S]

@StudRobotics, are you sure that the diffs are clicking? I see the CV-joints here, between the wheels and diffs and usually they're the weakest part in the drive train. Please check if the parts 92906 has some wear - they clicks usually, and the solution is to replace them by universal joints (cardans) with adjustment of suspension mounting points.

[suffocation]

Two ideas off the top of my head:

1) Get rid of those useless beams on the bottom (replace them with panels if need be), thus cutting the vehicle's weight and, consequently, the stress on the drivetrain.

2) Use live axles so you can mount portal hubs and gear down after the diff. Same outcome as above.

Edited August 21, 2017 by suffocation

[nicjasno]

It's much too heavy.

[BrickbyBrickTechnic]

Try to get rid of the 8tooth gears.

[nicjasno]

Just now, BrickbyBrickTechnic said:

Try to get rid of the 8tooth gears.

That is also a very good suggestion.

[Leonardo da Bricki]

Live axle with portal hubs for sure, or at least geared down like in Madoca's FJ40. And definitely get rid of the 8-tooth gears, and the rear differential. Keep the front one though.

[nicjasno]

Instead of the 8 tooth gears, use universal joints.

[suffocation]

Live axles would also provide increased clearance and give you a ton of room for diff locks, which can be pretty useful (and fun!) if you want to use the vehicle on rough terrain.

[MangaNOID]

I also had a rear diff clicking when any stress (minor)on the vehicle was had. I had portal hubs geared down, and the vehicle weighed 1kg.

I gave up. 

Are your gears old and slightly worn?

@Leonardo da Bricki how do you have a front diff but no rear diff? I tried doing that but could not get the gearing the same so the vehicle would acordian in or out with different wheel speeds.

 

[PorkyMonster]

I will add one more 20t gear, and fill the gap between the two cv joints, as follows, before trying anything more drastic:

[Leonardo da Bricki]

@MangaNOID You have to use the old-style differential with the 16- and 24-tooth gears. Otherwise, you are correct, it will not work. However, I believe that Efferman has created differentials similar to the new-style ones from Lego that allow equal gear ratios to be achieved.

[StudRobotics]

I didn't expect this to get so much replies overnight, and I'm pretty overwhelmed by all of them. I'm going to try PorkyMonster's idea first before the others, and then maybe Void_S as well. I also can't replace the 8t gears. Thanks for the replies!

[PorkyMonster]

12 hours ago, StudRobotics said:

I'm going to try PorkyMonster's idea first

btw, use two half-bushes or one full bush, instead of one half-bush (mistake in my picture above) to fill the gap between the two CV-joints. I'm sure that after this, it'll be impossible for those joints to pop out of their sockets, and you'll see how strong they actually are...

 

[Didumos69]

5 hours ago, PorkyMonster said:

btw, use two half-bushes or one full bush, instead of one half-bush (mistake in my picture above) to fill the gap between the two CV-joints. I'm sure that after this, it'll be impossible for those joints to pop out of their sockets, and you'll see how strong they actually are...

I think this is a very good idea. You are in fact 'form-locking' the CV-joints, which is a good practice in general to make sure parts don't get displaced.

Btw, your drive axles running to the front and rear diffs (green encircled) are completely covered by beams, bushes and connectors. It's not the cause of the grinding diffs of course, but it is likely that the bushes and connectors rubbing against the supporting beams introduce unnecessary friction. My experience is that it's better to leave axles uncovered if covering doesn't really add anything. I would get rid of the two bushes and the red cross block (red encircled) in your case.

[StudRobotics]

@Didumos69 Thanks for the advice, but I already fixed the issue. I had to switch the black gears as seen here.

Before

After

The gearbox I used for this entire build is Sariel's 4-speed, which I highly recommend using because it's compact, lightweight, and durable.

I just need to know which speed is which and change the programming for the EV3 brick a slight bit. Thanks for the help!

[steph77]

hello.

According to me you have to light it up at max and then you must simplify drastically the transmittion. You ave realy to much gearing in the process.

Try to have one solid reduction directly at the output of the motors in order to increase the torque as much as possible and the go in the most direct way to a differential.

 

@+