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Discussion Starter · #61 ·
Excellent progress... great info! I'm glad you did the oven test... and found that it wasn't going to hold up as well as the specs say. Better to see that before it's in a car!

FYI, not that this is necessarily a solution for you, but when we wanted to "quench" some of the stray magnetic fields (back in my semiconductor engineering days) we would put a u-shaped iron on the magnet, so that the field had a "path" to follow. Basically, if you put a metal cap on the disc-shaped magnet in your picture, it might help direct the stray field and keep it from going too wide.

I think the angled sensor is the best idea for now, or moving them a little further away if you can. Or maybe specifying a "weaker" hall sensor component.

In any case, you're all on the right track for sure! Just wanted to give a few other ideas/options.

EDIT: Here's a picture of what using metal to "short circuit" the field looks like:

The article may be related, but I thought the picture was perfect to show what I was trying to put into words.
Thanks for the link. Much appreciated.

PV has got some special magnetic field blocking material on order to see what can be done. Certainly the link provides some guidance rather than us just guessing.

That being said, it seems there is a lot of flexibility within the TCU when doing the cal. It seems to take readings of the magnet distance when a gear selected, but also with the possible pre-selections and keeps all these for reference as well. We are thinking that if we can just tone down the interference to a reasonable level it should be fine. It still seemed to be OK when doing the testing even though it was jumping a huge amount when other pre-selections were happening, so making this interference less by tilting back is going to reduce an issue that really doesn't seem to be an issue at the moment. We just want to make it better.

Regarding the melted wiring on the sensor after the test, I've spoken to PV about this and he said the wiring on this sensor was just some cheap stuff from the local electronics shop. He's sourced wiring good to 200 C for the real thing.
 

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The new wire has silicone insulation and is specifically rated for 200 C high temp installations whereas the original stuff was just standard thermoplastic insulation rated to 105 C, so we should be good there.

Funny thing on the test housing I forgot that I had it printed out of PA12 which melts at 186 C, for some reason I was thinking it was PA6 which is higher, around 210 C. I had never planned to actually put it in an oven but when jjrichar suggested it I said, sure why not just don't go above 175 C. Oops. Cool pictures at least.

I hope to have new sensors (housings still made with PA12 until we switch to aluminum) done in about a week incorporating all the lessons learned. Major changes are moving one sensor to the other side to improve linearity, changing the sensor angle to reduce magnet height sensitivity and improve channel to channel cross-talk, reduced sensor gain to eliminate railing, and setting lower clamping levels to eliminate TCU nuisance faults. We've also learned some very interesting things regarding when the TCU faults, hard faults vs. soft faults, and the meaning of some ambiguous faults people have reported in the past. That should help with troubleshooting PDK issues down the road.

Recurring costs on this thing are ridiculously low, not more than $100 in material and two hours assembly each in quantities of twenty. Not counting jjrichar's costs of acquiring the Demo car, I'll be surprised if we spend $1000 in development material costs.
 

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Discussion Starter · #63 · (Edited)
I finished the beating up on our sensor today. It's looking pretty battered and bruised. Amazingly it still works fine on all four channels. These hall sensors are pretty amazing in my opinion.

It spent the night in my freezer at about -20 C no issues.

I then connected it to an old chainsaw (without the chain and bar) and tried to vibrate the life out of it for about an hour. It's my old rescue saw I barely use because it vibrates so much. Perfect for the test. Still worked fine afterwards.

I then whacked it against a concrete floor a bunch of times, with bits being broken off in the process. Still worked fine.

Then I lined it up T-ball style and gave it a good hit with a home made cricket bat. It was a cracking hit and came right out of the middle. It flew off far quicker than I expected and hit my garage and put a good sized dent in the panel. My wife appeared moments later with 'that look' we all know and love. Still worked.

I lined it up again and gave it the best hit I could, but not aiming at the shed. It ended up about 30 m away. Electrical connector broke off, but after I pressed it back on the sensor still worked fine.

I'm a little amazed. I take my hat off to the people who design and produce these sensors. Close to indestructible. This gives me a lot of confidence that when we put it in an aluminium housing it will be a pretty solid unit.

What it looked like afterwards
Gas Auto part Cable Wood Electrical wiring


Video of the entire testing process. Electrical and in-transmission testing at the start and stress testing at the end.
 

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Excellent progress... great info! I'm glad you did the oven test... and found that it wasn't going to hold up as well as the specs say. Better to see that before it's in a car!

FYI, not that this is necessarily a solution for you, but when we wanted to "quench" some of the stray magnetic fields (back in my semiconductor engineering days) we would put a u-shaped iron on the magnet, so that the field had a "path" to follow. Basically, if you put a metal cap on the disc-shaped magnet in your picture, it might help direct the stray field and keep it from going too wide.

I think the angled sensor is the best idea for now, or moving them a little further away if you can. Or maybe specifying a "weaker" hall sensor component.

In any case, you're all on the right track for sure! Just wanted to give a few other ideas/options.

EDIT: Here's a picture of what using metal to "short circuit" the field looks like:

The article may be related, but I thought the picture was perfect to show what I was trying to put into words.
Nice article, thank you. As jjrichar mentioned I ordered some very high permeability magnetic shielding material made from cobalt alloy to do exactly what that picture shows. Fortunately the sensor angle changes seem to have largely mitigated the concern, but we'll add the material if needed.

In all honesty we don't even know if it's a real concern as crosstalk was small and it didn't seem affect gear engagement, but we may as well fix it why we are updating things.
 
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