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slowtwitch
01-30-2012, 07:28 PM
Hello folks, It's been awfully quite on the boards.....hope all is well :)

Anyway...I wanted to give you folks an update on my Mikini. I have finally been able to finish my first set of brackets for a throttle system that i have developed. It has only taken close to a year, thanks to this mill :mad:..... but, I finally did it. But, it wasn't without it's Mikini problems.

Ever since Mikini sent back my motor and boards, the machine ran, but, it just didn't sound right. For instance, at 3000 rpm there would be a slight change in speed...like it's skipping a beat. When i was machining the brackets, I had a couple alarms from overloading. The cuts were with a 5/16" rougher carbide end mill, at 3000 rpm, 020" depth of cut, 25 ipm, in 6061 aluminum.

I didn't want to touch anything and try to make any adjustments...since these machines are so delicate..So, I waited till I completed my first job.

Tonight, I decided to adjust the Hall sensor ring, in hopes of improving the torque and speed issues.

Here is what I found....

P1300002 - YouTube

Since the ring was loose, I had to figure out were the sweet spot is with the Hall commutation and set it. In my motor repair days, we use to set armature brushes by adjusting them while the motor was running.

So, i decided to do the same in this situation. I brought the spindle up to 3000 rpm and slowly turned the sensor ring clockwise till I went into alarm. I marked the location of a Hall sensor (that I will use as a reference point). I moved the ring back a little bit and started the spindle again and this time I moved the sensor slowly counter clockwise..till I went into alarm. Again I marked the location of the same hall sensor. Now i have two marks..then I just moved the Hall sensor that I used for reference, in the middle of the two marks....

I ran the spindle at 3000 rpm and made a very slight adjustment ...clockwise. This time I didn't hear any of the dips in motor speed. Here's were Mikini will probably flip...I designed my own dynamometer.....I kinda wedged a long 2x4 against the spindle, actually the top of the draw bar ( I did have it screwed into a collet) to see if i could cause an overload situation....I cut a nice half round shape into the 2x4 with the drawbar nut....and it didn't go into alarm :)

I know my sensor ring adjustment technique will probably make the hairs on the back of the Mikini folks stand on end, but, I don't care. My goal is to have a running mill...and I will take unorthodox methods to get it to that point.

SWATH
01-30-2012, 09:59 PM
After getting my parts back from "repair" I looked everything over and found that one of the three wire from the hall sensor ring was literally hanging by a thread right where it is hot glued to the ring. I mean all of the little wires were frayed out and it was connected by only one strand and in fact the last stand gave way while I was gently inspecting it, so I had to carefully solder it back together.:mad:

My spindle is still hinky. It will only get up to about 3300rpm still. Mikini said they would investigate the matter after I sent them a video of it and within a few days they said that they were able to reproduce the problem and would have a write up about it to me in the next couple of days. Well a month passed and I didn't hear anything so I again asked about the write up they were going to get to me. They said that they had assumed the problem was resolved:confused: but would find the write up and get it to me anyway, mentioning it was likely a problem with unbalanced legs on my power supply. I haven't heard from them again and I never got the write up. In case you were wondering each leg of my power supply is within .3V of each other relative to ground. I've adjusted the seemingly cheap and fragile hall sensor every which way you could imagine and it doesn't help.:mad:

I've since reprogrammed how I was doing toolpaths to try and get more of a HSM type strategy with very light WOC and many passes. This actually works fairly well with the the higher RPMs (~3000). Although my CAM doesn't support HSM yet I've been spending a lot of time trying to get spiral pocketing to kind of do it although not nearly as efficiently. I've also been drilling out .5512 holes first to get my .5in. endmills in there without plunging and chipping the tips off. I wish I could use a bigger drill but this sort of works for now although it's very time consuming. I'm pretty much pushing the spindle to the limit and it takes 21min to drill 3 holes 2.5in. deep. Oh and one last vent. When I got my stuff back I found that the green and yellow ground wire on the top of the motor was loose so I tried to tighten it. It didn't tighten, then i realized that the hole was either stripped out or the wrong size but the screw was just sitting in the hole loose. I had to re-tap it and install a larger screw to ground the motor. I mean how do you miss these things when the thing is in for repair for the 2nd time.

Oh how I long for the day when someone much smarter than me gets a working spindle upgrade that I can copy.

Also Mikini freaked when I sent a video of me tuning the sensor ring while the motor was running. I think they said it could damage the electronics or something.

slowtwitch
01-31-2012, 06:06 AM
Also Mikini freaked when I sent a video of me tuning the sensor ring while the motor was running. I think they said it could damage the electronics or something.

That's funny...lolol But, it's ok to have a loose sensor ring dancing around under the cap or have broken wires.....amazing!!!!

It's just a matter of time till I rid myself of all the Mikini electronics and install a spindle and electronics that would be so many times better......the time will come :)