Author Topic: CNC router table... (Read 19332 times)

John Hill · « **Reply #25 on:** January 14, 2015, 09:23:02 PM »

Too many coils in parallel is a bad idea,

with 6 coils in parallel the resistance is only 0.3 ohms and the driver shakes it head when presented with that load.

John Hill · « **Reply #26 on:** January 15, 2015, 02:48:44 PM »

Just three coils, one for each phase, runs very fast, so fast I chickened out and did not take it to the maximum fearing the rotor will fill my workshop with flying bits of plastic and small magnets.

So what can be gained from this information? Obviously there is nothing to do with the characteristics of the individual coils or magnet circuits that prevent high speed operation and also obvious is that the controller and driver circuits can drive to high speeds.

The challenge now is to arrive at a configuration that is optimum for this combination of F@P and these driver bits.

vtsteam · « **Reply #27 on:** January 16, 2015, 09:28:27 AM »

John Hill · « **Reply #28 on:** January 16, 2015, 01:52:22 PM »

I did a test yesterday with the cut down stator and found low speed torque 2.6 Nm (about 350 ounce inch) of low speed torque and a free running speed of 500rpm. This is with each phase consisting of 6 coils in series parallel configuration of 3x2.

Considering my earlier test I believe this is the most practical configuration for this motor with the power supply and drivers I have on hand. Considering also that I am using only 18 of the original 42 coils I expect more powerful drivers would get at least 5.5Nm of torque, maybe more.

If I were to add more coils that would mean more in series which would reduce the voltage across each coil and increase the inductance.

The drivers say they are good for 60 volts, 8.3 volts peaks and 5.9 volt rms, maybe if I stub my toe on a 50v transformer!

vtsteam · « **Reply #29 on:** January 16, 2015, 07:13:00 PM »

Two matched 30's with secondaries in series would get you 60V. But you have to phase them properly or you won't get any voltage.

I've done the same to increase current capacity instead by parallel connectingl, but then you ABSOLUTELY must get the phasing right, or it's a short circuit for both.

John Hill · « **Reply #30 on:** January 17, 2015, 02:27:04 AM »

I have a power supply lashed up on the bench. 30 amps at 62 volts but I would really like it to be closer to 55 volts. No taps left on the transformer to reduce the voltage.

awemawson · « **Reply #31 on:** January 17, 2015, 03:14:56 AM »

Any room on the transformer bobbin to wind any extra coils ? If so connect in opposition to reduce the effective number of turns on the secondary. I've used this technique several times when making phase converters from standard isolating transformers.. Transformer construction needs to be suitable to thread the wire round the bobbin without dismantling.

Jonfb64 · « **Reply #32 on:** January 17, 2015, 03:57:43 AM »

How about winding a new secondary onto a microwave transformer. It's easy to remove the old secondary which leaves plenty of room to wind a new one. I have used one to make a small 800 amp spot welder. Check out YouTube plenty of info of stripping one out.

Jon

John Hill · « **Reply #33 on:** January 17, 2015, 04:09:23 AM »

No room to poke any any turns on the secondary but I might be able to get the desired result by winding a few turns off, maybe tomorrow. Perhaps I will look at a microwave transformer after that!

John Hill · « **Reply #34 on:** January 18, 2015, 04:21:29 AM »

I managed a little surgery on the transformer taking 5 turns off the top of the secondary, no load voltage is now 56 volts which I thought would be comfortably within the 60V spec of the driver however stalling the motor causes the driver to go into alarm, I dont know if that is over voltage or over current.

PekkaNF · « **Reply #35 on:** January 18, 2015, 04:38:03 AM »

Quote from: John Hill on January 18, 2015, 04:21:29 AM

I managed a little surgery on the transformer taking 5 turns off the top of the secondary, no load voltage is now 56 volts which I thought would be comfortably within the 60V spec of the driver however stalling the motor causes the driver to go into alarm, I dont know if that is over voltage or over current.

My limited experience tells that if the drive has regenerative braking and it is decelerating you may get over voltage if the feeder is weak (can't absob current and that will cause voltage rise).

Overcurrent means too fast ramps or too much torque demand.

Pekka

vtsteam · « **Reply #36 on:** January 18, 2015, 08:50:13 AM »

The driver seems weird though. If it says 60V spec, and you can set the current (usually with a DIP switch setting), it should handle everything in a 56V setup.

It is supposed to limit current, and it is supposed to operate with 60V input, and it is supposed to operate a motor and hold position, when needed, (ie a stall) so what should be wrong?

Is the 56V clean DC?

Are you running through a rectifier bridge with adequate filter caps?

The only other possibility is that there's some current rating for the driver (not the current setting), and it doesn't like the low resistance of your motor @ 56V -- 56V pushes too much current for the driver max rating.

vtsteam · « **Reply #37 on:** January 18, 2015, 09:04:05 AM »

One more thought:

56V is measured DC after the bridge and caps -- I hope,

not just the AC (or Xformer rating).........

DC would be considerably higher if it is.....

awemawson · « **Reply #38 on:** January 18, 2015, 10:03:00 AM »

IIRC the original Gecko drives needed a large electrolytic capacitor close to the driver 'to absorb the over run current'

John Hill · « **Reply #39 on:** January 18, 2015, 01:36:03 PM »

The voltage is measured at the filter capacitor which is a beer can sized 3600 150VDC. I can add capacitors on the motor leads but that seems counter productive.

Maybe I should take my wife on a two hour drive and buy some 56Volt zeners.

This is a 3 phase motor so I guess I would need half a dozen diodes.

John Hill · « **Reply #40 on:** January 20, 2015, 04:48:16 AM »

I wired another stator today, using all 42 coils, every phase 4,4,3,3 in parallel and it is not a very good performer at all on 55volts 6 amps.

John Hill · « **Reply #41 on:** January 21, 2015, 01:17:09 PM »

I had another try with my latest rotor and managed to measure nearly 6 N.m. of holding torque. It also free runs up to 300rpm. That is using every coil configured every phase 4,4,3,3 in parallel. The three phases are connected in delta.

I think it is time to start building the machine.

vtsteam · « **Reply #42 on:** January 21, 2015, 03:03:18 PM »

Well that's nearly 1000 in oz. ! Should do the job.

John Hill · « **Reply #43 on:** January 21, 2015, 03:09:17 PM »

What would a 'regular' stepper with that torque cost do you think?

vtsteam · « **Reply #44 on:** January 21, 2015, 03:22:30 PM »

From $100, on up, here, depending on country of origin and the firm selling it.

bertie_bassett · « **Reply #45 on:** January 21, 2015, 03:30:01 PM »

where do you find all these usefully moddable motors??? starting to get jealous.

John Hill · « **Reply #46 on:** January 21, 2015, 03:37:39 PM »

These motors can be found at the roadside on council clean up days in New Zealand and Australia. They are the motors from Fisher and Paykel Smartdrive washing machines, since 1992 but similar motors are now to be found in Samsung and other makers.

bertie_bassett · « **Reply #47 on:** January 22, 2015, 01:11:52 PM »

ill have to keep an eye out. cant say iv ever seen one with a motor like these in them over here though

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Author Topic: CNC router table... (Read 19332 times)