PID tuning will change the extraction profile for any given ball material, so any real effect purely from different materials is confounded by changes to the PID profile, making it even harder to tease out the effects. I ended up with the zirconium bearings, and am currently retuning the PID to see if that changes anything. Got a tiodw mini to play with too if I really want some variables to sort out.
Anyone else noticed this and found noticable differences after the PID was re-tuned to suit the thermal profile of the new combination of materials?
The coil tuning isn't going to have much, if any, effect on the actual hit. There's just no way to get enough heat calories from the coil, thru the head and into the balls within the duration of a 15 to 20 second hit. Add to that the fact that you're actively cooling the balls with the airflow and likely have a *LOT* of momentum on that cooling before the pid controller starts ramping up the duty cycle. The controller has a major uphill battle at that point.
On the subject of duty cycle, think about how much your temperature drops during a hit. Maybe 15 to 20 degrees on most heads... 35 to 45 on the ones where the coil extends down past the ball chamber. That's likely not enough of an offset from the target/set temp on the PID controller for it to ramp up to 100%, so it may not drive the coil very hard to recover that lost heat; certainly not as hard as during the initial heat-up. Meanwhile, the balls have dropped 100F, 150F... maybe even more.
The closest I ever came to that level of efficiency was with one of my 16mm rTiTi heads. From hitting it, I actually felt like it was able to keep up with my hits - it felt like it had endless vapor. My temp logger setup (4 channel 100ms sampling meter, air pump, flow meter, tons of tubing, bit of blood) showed that not to be the case, however - the calories were definitely not being replenished at 1:1. That probably was my most efficient head, tho.
In the case of the current ball vapes, the coil tuning is about what happens between the hits, during the initial heat-up and the recovery. It can make an improvement in how quickly the coil reaches the target temp but keep in mind that, in most cases, the balls are NOWHERE near the same temp at that point; they lag behind by a lot, especially with the heads that have thicker ball chamber walls.
retuning PIDs is best done from cold AFAIK to get the ramp-up phase right.
That'll probably just drag out the process. I've never really dug into what the controllers are doing during the auto-tuning, but I bet it's a pretty simple process on most of them. Something along the lines of:
1. Shoot for XX degrees over the target temp and then XX degrees under the target temp. Calculate new PID values based on the overshoot/undershoot.
2. Using the new values from #1, repeat the process
3. Using the new values from #2, repeat the process
4. Done. Save the new values from #3
Edit: I just noticed the image with the table is broken. Here 'tis again: