Figuring out what kind of move is being executed?

I tried lamp oil, fuel oil, various flavours of low viscosity hydraulic oil, silicone oil and naptha. All of them have problems when the probe is triggered and then slowly released. Works well for 1000 trigger actions, but number 1001 and it takes seconds to make contact again. It is not that there is no contact at all; contact resistance keeps on hovering in the 100-200Ohm range.
Increasing contact pressure does not solve this. I also tried increasing contact measuring current from 15mA max to 80mA max (it doesn't reach that when resistance is 100+ ohms with only 3V supply), no success. Once I use the lab supply set at a higher voltage contact resistance instantly drops to a normal 1-2 Ohms.

Thus, somehow a few liquid molecules stay between the contact patches of ball/rod. If I use a higher voltage I manage to burn the contacts free of that, but that's playing EDM machine...

Argon does not suffer from this. Works perfectly, just as well as air. I only wonder how long it would take for the argon to diffuse through the nitro-butyl rubber bellow (and PCB, but that one is 98% copper on the bottom) that seals the contact chamber. Or a better question: how long would it take before moisture and oxygen levels inside the chamber are high enough to cause corrosion of the hardened steel contacts...

have you tried gold plating the balls etc , although removing the chrome may be the worst point ,

how much current and voltage are you dealing with across the contacts ? i.e on a contact break & on contact make


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i think we can solve this .

cncbasher wrote:

have you tried gold plating the balls etc , although removing the chrome may be the worst point ,

No, I haven't.
Gold is not very suitable for switching contacts. For stationary contacts it is, because it tends to weld to itself under pressure and forms a gastight and excellent conducting seal that way. Once you break the contacts, you also tear a layer of gold apart. See what happens with 3.5mm headphone jacks; after 300 insertions the gold is gone.
A better material would be palladium or so. Could as well be unobtainium.

BTW: If I wanted gold plated balls and rods, I would visit the local body piercing shop. Dumbells (or whetever they call them) are available in all sorts and sizes.

how much current and voltage are you dealing with across the contacts ? i.e on a contact break & on contact make

voltage over the contacts is CR2032 battery voltage: 3V.
Current through the contacts is currently 15mA max, but as soon as I detect a low resistance I switch off the current for ~50usec to prolong battery life and reduce load on that 2032 coin cell. This does add a little latency on break.
On make voltage is present 100% of the time, until contact resistance is low enough. Thus, no additional latency on make.

( sent you pm )
i think we can solve this .

Where do I see PM's? Didn't know we had such a feature here. Didn't receive a notification either.
You can also mail me at dabit a icecoldcomputing point com

andypugh wrote:

Tungsten Carbide is (surprisingly, perhaps) conductive. I don't know if it is subject to oxidation, but I think that the rods (at least) of my Renishaw probe are carbide.

If I ever build a v2.0, I think I would indeed use tungsten carbide. The rods are no problem (I never break an 1/8 endmill, *cough*). But this time I just happened to have 6mm steel balls and 3mm ground steel pins in the correct length.