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eldata
02-21-2007, 09:39 AM
Can someone answer the following;

1. What's the no load RPM of this motor? Over 6000 RPM seems a bit high to me assuming the voltage constant is off by a factor of 10.

2. Does this motor have a skewed rotor or not?

This photo seems to say yes;
http://www.kelinginc.net/KL34-150-90Skewed_Rotor020.jpg

But this "review" seems to say no;
http://www.kelinginc.net/KL34_150_90_TestResults.pdf

What's missing here?

Larken
02-22-2007, 08:10 PM
This motor has a skewed armature, and works well as a servo.

Maris's review is wrong, as he assumed they didn't.

I've tested them with my Viper drives and they worked well. I will post a video of them running.

They run about 6000 rpm at the rated voltage, but run a lower power supply voltage to match your needs.

eldata
02-22-2007, 09:29 PM
>This motor has a skewed armature, and works well as a servo.

Okay, thanks.

>They run about 6000 rpm at the rated voltage

Assuming encoder mounted on the motor, this means a 50kHz step rate would be required for maximum RPM with a 500CPR encoder and 1X quadrature decoding. Explains why a 200CPR encoder was used in the review since the Gecko 320 is only 4X. The Gecko and this motor isn't exactly a match made in heaven.

If used with a 250CPR encoder on the motor, 90V drive with 1X decoding, 4:1 stepdown pulleys and the equivalent of a 10TPI screw, I estimate continuous torque of at least 300 oz-in, step resolution of .0001", 120-150IPM rapids and a step rate requirement of less than 25KHz. If the servo drive can manage a following error of less than 10 steps while cutting at 100IPM maximum then this would be a reasonable setup IMO.

H500
02-22-2007, 11:05 PM
Larken, can you tell me what the total cost was to ship your motors to Canada?

Larken
02-25-2007, 12:05 AM
I don't sell the motors, just the servo drives.

http://www.larkencnc.com/viper/index.shtml

Mariss Freimanis
03-01-2007, 08:21 PM
Larken,

The motor literature originally described the motor as having an unskewed armature and the motor does have significant cogging below 1.2VDC. I took the literature and observed cogging as indicating an unskewed armature.

I took the motor apart as a consequence of your message and saw that the armature is indeed skewed.

While we're at it, it would be good when you compare your product against ours to give a fair comparison. The information you have for our G340 is factually wrong:

1) "X1 quadrature decode". Wrong. The G340 uses X4 quadrature decode.
2) "Programmable step size--NO" Wrong. The G340 has 1, 2, 5 and 10 step sizes.
3) "Warrantee---NO" Wrong. We have a 1-year warantee.

It would be nice if you corrected these errors in your table. We avoid such comparison charts for that very reason and because they appear mean-spirited.

Mariss

smoker
03-02-2007, 03:00 AM
Hi Mariss, thanks for clearing this up.
I am in designing phase and saw that table as well and was very concerned as I wanted to use the G340.
So, at what is the rate that the 340 can receive encoder input?

Just I saide question, the motor is rated at 4200RPM@90V, If you say that cogging starts at 1.2V (factor 75) does this mean that the motor is cogging at about 4200/75= 56RPM?

David

Mariss Freimanis
03-02-2007, 10:13 AM
1) The maximum frequency is 250,000 step pulses per second. Most phototransistor type encoders have a 50kHz maximum channel output (CH_A, CH_B) frequency. This makes for a 200kHz maximum encoder count rate when using a 'X4' quadrature decoder. Phototransistors are not real fast.

The G320 / G340 uses digital noise filtering on the encoder inputs. The filter prevents the drive from 'seeing' anything narrower than 5uS on the encoder inputs. Most noise pulses are narrower than 1uS so the drive is virtually immune to noise.

2) A good servomotor has no variation in torque with shaft position while a 'utility' DC motor's torque varies with the shaft angle. 'Cogging' (speeding up, slowing down) as the motor turns very slowly shows this behavior when the motor is driven with a very low DC voltage.

A servo drive expects the motor constants (Kt, Kv) to be constant; cogging means they vary with shaft angle. The more they vary the greater the cogging. By comparison, I have a $500 Baldor NEMA-23 motor that turns very smoothly at 15 RPM with only 0.31 VDC applied.

Cogging has no practical meaning other than to tell the quality of the motor.

Mariss

Larken
03-02-2007, 02:32 PM
I took the motor apart as a consequence of your message and saw that the armature is indeed skewed.
You shouldn't assume things and publish them in a paper.



While we're at it, (at what)? it would be good when you compare your product against ours to give a fair comparison. The information you have for our G340 is factually wrong:

1) "X1 quadrature decode". Wrong. The G340 uses X4 quadrature decode.
2) "Programmable step size--NO" Wrong. The G340 has 1, 2, 5 and 10 step sizes.
3) "Warrantee---NO" Wrong. We have a 1-year warantee.
It would be nice if you corrected these errors in your table.


2) "Programmable step size--NO" Wrong. The G340 has 1, 2, 5 and 10 step sizes.
This is selectable, not programable.

3) "Warrantee---NO" Wrong. We have a 1-year warantee.
I was going by the fact that you wouldn't replace defective drives used by by ex-partners (marc's) company a few years ago. From what I understand now, you will replace only 1 drive.



It would be good when you compare your product against ours to give a fair comparison.
We avoid such comparison charts for that very reason and because they appear mean-spirited.
But you compared the lowcost servo motor against the expensive one, didn't you. ? Was the other a 4 brush motor with the low cogging , you were comparing against a 2 brush?

Mariss Freimanis
03-02-2007, 03:55 PM
OK....

1) I'll take your criticism to heart and endeavor to never "assume things" again in the future. Stuff like manufacturer's literature that says the armature is not skewed. I promise I will take step motors apart in the future to verify 1.8 degree motors actually have 50 poles by counting them.:-)

2) Distinction without a difference.

3) Yeah, we have lousy after market support. We have never repaired customer damaged drives for free including return shipping. We have never done that even though the drives may be 5 years out of warranty. We have never had a "one time, stuff happens deal" where we replace drives for free when someone has reversed power polarity for instance. We never spend time on the phone to give application support or spend time posting helpful articles on all the groups. We certainly haven't given away hundreds of drives for charitable causes around the world. We pretty much suck and your friend's experiece proves it. We're just in it for the money turning out defective drives.

4) You kind of missed the point. I was making the point this was an exceptionally good motor given the price and an excellent value.

Mariss

P.S. A quick trip down memory lane: Are you the same guy that called me up late at night about 5 years ago and cussed me out for making inexpensive step motor drives? How doing that was ruining the market, how drives should cost $300 or more and how making $100 drives was putting good people like him out of business? The guy's name was Kenny or Larry or something if memory serves.

Larken
03-02-2007, 10:25 PM
The guy's name was Kenny or Larry or something if memory serves.
Yes i'm Larry kenny of Larken Automation, (www.LarkenCNC.com) did you just put that together now ?
(I've only been in this scene for 17 years making CNC routers and drives)

Haha, Ya you were bragging about how it was just the two of you with a pick and place machine, selling all those drives cheap. Good for you, I guess you've sold a lot.

BTW, I've sold a lot of my Cobra stepper drives for Bridgeport retrofits to replace blown gecko's as well.

Cool off Maris, Lets not turn this from CNC-ZONE to CNC-WARZONE.

Mariss Freimanis
03-02-2007, 11:16 PM
Yes, I did just now put it together.

Larry, good to speak to you again after 5 years. I enjoyed our spirited exchange of views the last time we spoke on the philosophy of business and competition. It was memorable and I remember it with a certain paradoxical fondness.

Thanks for reminding me of the old days. Yes, it was "just the two of us with a pick and place machine". The evil and cantankerous Ursulla pick and place is no more. It was replaced by 3 reliable machines with no names that run 3 times faster each than Ursulla ever did. They were paid for by "selling all those drives cheap". People got a lot of cheap drives, in return we got a lot of machines to make even more cheap drives. Nearly everyone is happy with that exchange.

Larry, it's not CNC-WARZONE. I'm mild-mannered and decidedly unwarlike in demeanor. I was simply racking my brain why you are gunning for me in your post and that tripped a 5-year's old memory. I took a flying guess and it seems it was right. I apologize for the name transposition; it was not intentional nor meant as a slight.

I'm happy to hear of your success with your Cobras and Vipers and other snake stuff. I wish you more of the same in the future. You and I had a gentlemanly philosophical disagreement regarding the nature of markets. The wonderful thing is we each can practice our divergent beliefs in that marketplace and let the marketplace laboratory decide which is the better way to go. I know the customer benefits either way and makes the decision.

Best of success,

Mariss

smoker
03-04-2007, 05:58 AM
Hi Mariss, if I was going to buy this motor with a 250 cpr (1000 ppr) and run it at 3000 RPM the encoder input would be 50kHz.
a/ Is this OK for the G320?
b/ do i need the G320K wich has a different capacitor? (or can this be done by me) I have no SMD soldering device....

David

Mariss Freimanis
03-19-2007, 01:16 PM
1) Correct. 3,000 RPM is 50 revs/sec, 250-line encoder is 1,000 steps/rev. Maximum step pulse frequency becomes 1,000 times 50 or 50kHz.

2) No need to change anything. Leave the cap as is.

Mariss