LDU mechanical failure

[jon volk]

It was only a matter of time till something showed up. This unit has seen hundreds of WOT launches, many on slicks. On street tires if traction breaks, it will induce wheel hop, which is quite damaging on its own.

I was powering up a hill as the car shut off and made a whine on deceleration. I did not think much of the sound at the time as the motor was completely dead. As in no precharge, no wifi, nothing. So after some troubleshooting I found there was no power after the regulator on the logic board. This was traced to a broken solder joint on the inductor. Some solder and hot glue for added support and we're back up and running...or not. Powering up the motor resulted in a loud gear noise so I tore it apart. It seems the broken solder joint was likely caused by the shock of the diff exploding.

The bad news is I have to find another set of gears.
The good is that the inverter and motor pinion look fine and I have a Quaife LSD on the shelf that I've been neglecting to install.

There was a good amount of crap in the diff fluid so this likely could have been caught before failure with frequent fluid checks/changes. I would also think that a Quaife diff is a good investment as well.

[JaniK]

Goos to know...

So the addition of an oil filter in model 3 could take some of the metal flakes in before the wear the gears itself?

[jon volk]

Couple more

[P.S.Mangelsdorf]

Looks like maybe the shaft holding the spider gears snapped, and then the gears ate themselves?

Or do you think the gears were wearing and their failure broke the shaft?

[jon volk]

Based on the wear on the outer surface of the spider gears facing the carrier, I believe they were eating themselves up prior to the pin breaking.

[P.S.Mangelsdorf]

Based on the wear on the outer surface of the spider gears facing the carrier, I believe they were eating themselves up prior to the pin breaking.

I wonder if they seized on the shaft. Seems odd to me that the shaft would break after the gears.

[jon volk]

That’s my guess is the clearances got to a point of bind. Sort of like running a bent connecting rod until the piston cocks in the bore and the wrist pin gets ripped out. Not that I’ve done that or anything.
It is certainly possible the pin went first. The end result is the same.

[P.S.Mangelsdorf]

The end result is the same.

Very true. Best of luck finding new gears.

[TheSilverBuick]

That’s my guess is the clearances got to a point of bind. Sort of like running a bent connecting rod until the piston cocks in the bore and the wrist pin gets ripped out. Not that I’ve done that or anything.
It is certainly possible the pin went first. The end result is the same.

haha.

That's impressive. Hopefully the damage is as contained as your initial assessment. Picture of the vehicle?

[jon volk]

Picture of the vehicle?

https://www.instagram.com/tesla_bimmer/

[Roadstercycle]

Jon, jump on YouTube and hunt down the guy who tore apart a Model s motor just to get YouTube clicks. Maybe he still has the parts you need.

[Roadstercycle]

Jon, jump on YouTube and hunt down the guy who tore apart a Model s motor just to get YouTube clicks. Maybe he still has the parts you need.

Here it is.

[bobwind]

I am going to be swapping the gears on my ldu's for the 4.5:1. If you can't find a set we can work something out. I'm probably 2 months from tearing them down. I think I know someone that has a dead ldu too. I'm close to you John in Boston, if your are in Ct. Pm me.

Bob

[jon volk]

I am going to be swapping the gears on my ldu's for the 4.5:1. If you can't find a set we can work something out. I'm probably 2 months from tearing them down. I think I know someone that has a dead ldu too. I'm close to you John in Boston, if your are in Ct. Pm me.

Bob

I found a spare set that should be coming next week as well as a full drive unit. When you have them out let me know. I may pick that set up as a spare now that I know what can break. I’ve had at least 3 sources confirm they’ve seen broken differentials/reduction gears so that seems to one of the weak points.

[bobwind]

It definitely is. The issue is these boxes a 1) geared for a 4800 to 5000 pound car. Drop the weight in half and you have too much torque for any tire to handle. You are going to be loading the gear box all wrong as the tires spin and catch. And b) designed to have traction control so you do not over load the boxes.

What we need is a 6 or 7 to1 gear set and a really good break based after market traction control system.

On my car I am running dual base units in the rear, locked diff, 4.5 to 1 gears, each motor driving 1 wheel. In the front a sport unit, with same gear, and a open diff. I am going to use the racetronics GPS and wheelspeed traction control system, but I think one could do it all in the inverter if they were clever, which I am not. Car is going to be about 3600 pounds, and this gearing is still not perfect, I probably will not have to much torque off the line, with out drag slicks, and even then it will be tough. Ideally I want a 7:1. It would be interesting and probably profitable to make a variety of drop gears for the ldu and sdu, and educate people about gear ratio to car weight in single gear cars. It is something most swap people overlook until the project gets on the road.

[jon volk]

What chassis are you using?

Agreed on the gearing. Even from a usable top speed perspective 9:1 is tough with a 25” tire. 4.5 goes a bit too far for my purposes so a 7:1 would be a great middle ground. Until then I’m diving in the rabbit hole of managing things electronically and already starting on v2 of my VCU.

[johu]

I've implemented traction control using the stock ABS sensors. Very simple, but I "only" have 100 kW available and just one driven axle so I can take the "real" vehicle speed from the undriven axle and control the driven axle to match that +X

[bobwind]

My chassis is a rcr superlite coupe. Aluminum semi monocoque, basically a semi street legal track car. It is a lot of work to convert over to electric, but it was the best platform I could find without building new from the chassis up.

I really like the GPS and wheel sensor solution racetronics uses in concept, but I have not seen it in action yet. Zero ev is said to have a open inverter fork with TC enabled but I don't know much about it or how it works.

[jon volk]

Sounds like an awesome project. I have a dual vr sensor conditioner in my VCU for taking wheel speeds off the abs sensors but haven’t implemented anything code wise yet there for TC. With slicks traction wasn’t really a big concern. Without the instant there was slip it induced wheel hop so traction control wouldn’t necessarily solve that. The threshold for normal wheel speed differences would mask such minimal slip. I need to solve that issue with proper dampers then focus on reeling in wheel speeds. Tesla had a few years and an army of developers to work all that out. I’m just an idiot bashing the keyboard until stuff compiles.

[johu]

You can find the relevant code here, I hope it's self-explaining: https://github.com/jsphuebner/stm32-car ... r.cpp#L358
Obviously wheelXY are the ABS wheel speeds obtained via CAN, throtmin/max is transmitted to the inverter. The actual control method is just a P-controller with a gain of -10
diff subtraction would have to be swapped for rear wheel drive.

[bobwind]

Ok makes sense. for awd you would need to compare all four wheels, or through a GPS on the Can and have it calculate expected wheel speeds for a given mph to compare too.

This sounds good for straight lines, but in turns the left and right wheels need different speeds. And in a car with 3 or 4 motors you can adjust one set or all wheels independently.

I have been thinking about something very similar could be used for torque vectoring if you had steering wheel rotation input, and maybe a IMU on the Can. I even played around with the idea of a lever on the steering wheel that can real time front/rear and left/right bias the power delivery.

[jon volk]

...and there were two. Replacement LDU going in the car and a fresh set of gears to repair the original as a backup.

*not sure what’s up with the orientation. They’re straight on my phone

[mohalkh]

...and there were two. Replacement LDU going in the car and a fresh set of gears to repair the original as a backup.

*not sure what’s up with the orientation. They’re straight on my phone

where can i buy a Tesla unit drive for mercedes b250e?

[jap]

where can i buy a Tesla unit drive for mercedes b250e?

https://finndel.no/bildeler.aspx?bk=354705&dk=0137

[jon volk]

Back in action.



Interesting observation is this motor is much quieter than the last. There was a pronounced whine, only when the inverter would start pwm generation that is notably absent from this one. It is a lower mileage, newer revision.