Servo Motor Recommendations (Mariss was right!)

[Adamj12b]

So I finished converting my Jet knee mill about 2 weeks ago. I was having some trouble with the encoders when I hooked up the motors to my 320's. I ended up calling gecko drive and talking to Mariss. He figured out the the motors that I am using were only about 72 watts. With their peak current being 12 amps, he said that I should not run them above 2.4 amps, At All!. He also said that they should not get more then warm to the touch.

So we ended up getting it running. The encoders I am using are 1024 line Lucas Index encoders and draw 124mA of current. So I had to wire up separate 5 volt power supplies to run them. Mariss told me that I needed 1 power supply for each encoder, Not sure why, but thats what I did. Turns out that problem was the common ground for the encoder has to be connected to the ENC- terminal, because the power ground terminal is a dirty ground, which was causing the problem. Everything works good, except with the encoder count being so high, the rapid speeds are slow. I am still playing with the kernel speed, but with too fast of moves the charge pump will shut the system down.

So anyways I am looking for some new servo motors for my mill. The Z axis one was extremely hot the other night after about 30 mins of running. I almost couldn't touch it. I noticed it when I started to smell it, but I figure Im too late now to save it.

I have been looking at buying one of these KL34-180-90 Keling 1125 oz-in servos for the Z and some of the KL34-150-90 for the X and Y when they are needed. The X and Y motor have not even gotten warm yet, but I figure once I start really using the machine they will.

Are theses good motors to use with the 320's? I plan on buying new encoders when I buy the motors. They sell US Digital E4's and E5's. 200, 300, and 500 CPR ones. I was thinking about going with the 300 line ones, but Im not sure.

I will be purchasing the new motor(s) starting in about 2 weeks when I get back from vacation. I have also attached a picture showing the motors current setup.

Adam

P.S. Here are the motors that you shouldn't get for your machine:http://www.surpluscenter.com/item.as...-2351&catname=

[timbeaulieu]

I'm glad you posted this. I was looking at those Surpluscenter motors for a project too. Thought they could have handled 10 amps. Didn't know that they couldn't or shouldn't be run at the higher amps. Sure glad Mariss helps the hobby community. I've read some posts on the internet and people claim they are using them on full sized bridgeport mills. Guess they are mistaken about what motors they have. I've heard and read nothing but good things about Keling products. The 1125 oz-in are 90v 40a max. The Gecko's are 80v 20a max. I was thinking that the 850 oz-in Kelings would be a good fit for the Gecko's. They are 72v 40a max. They spin about 4200RPM so with a 4 or 5 to 1 reduction maybe even higher you would have some serious power and pretty high speed rapid.

Thanks again for letting us know about the Surpluscenter motors. I've seen a lot of people ask questions about them.

[CarbideBob]

Peak current and peak torque tell you nothing about the performance of a servo motor.

If a servo motor runs anywhere near peak for any amount of time it will get hot, melt the brush holders, melt the wiring, and the grease will run out of the bearings. All not good things.

I can certainly attest to the fact that a stalled servo motor at peak torque will go up in smoke in a manner of minutes.

You size a servo motor by it's continuous ratings. This is the power it can tolerate for extended periods of time without damage.

It is possible to use power above the continuous ratings during accel and decel if the duty cycle is low enough. However you will get brush arcing and the motors life will be reduced.

Bob

[ckm]

I think you should get the KL34-170-90 instead of the KL34-180-90. The reason is that there is not much performance difference, except that the optimal voltage and current draw for the KL34-180-90 is higher than what Geckos can sustain. I just bought three KL34-170-90 and a power supply from Keling a couple of weeks ago.

Also, I recently purchased some AMT-102 encoders from Digikey (http://search.digikey.com/scripts/Dk...me=102-1307-ND). These are capacitive encoders instead of optical and the resolution is adjustable from 48 to 2048 ppr. They are also cheaper at around $30 and will fit shaft sizes from 2mm to 8mm and from 1/8" to 1/4".

HTH,

Chris.

[Adamj12b]

Wow those encoders look great. They only use 10 mA of current also. I think I might replace the encoders I have now with those and when I get new motors I can just switch them over. Do you have any picture of your setup?

Adam

[Mariss Freimanis]

Thanks for the info! It's the first I've ever heard of these encoders. 10mA, settable resolution and cheap price seems like a winning combination. I'm going to get 10 or so Monday and check them out.

Mariss

[ckm]

Originally Posted by Mariss Freimanis Thanks for the info! It's the first I've ever heard of these encoders. 10mA, settable resolution and cheap price seems like a winning combination. I'm going to get 10 or so Monday and check them out. Mariss

Before you get your hopes up....

I've got three KL34-170-90 with these encoder on them and three g320's, but nothing is hooked up yet, so I don't even know if they will work. They theoretically should, but who knows....

I'm going to bench test everything, probably in the next few days. Someone else on the 'zone is using them, that's how I discovered them, so I can't take all the credit.

I will say, these encoders are really nice. The come with a kit with a huge number of shaft sizes and tools for fitting them properly. There are also two bases with a large number of mounting holes that would fit pretty much any situation.

Chris.

[H.O]

Hi,
I have one of those, it works ;-) And, as you say Chris, it comes with bushings for all kinds of shaft diameters. If you do buy one Mariss, it would be really interesting to have a verdict on how they compare to a optical device.

/Henrik.

[Mariss Freimanis]

My interest in them is for the step motor PID servo project since we are planning to supply encoders with the drive (a long way from being finished). I will certainly put them through the wringer to see if I can tease out any problems.

Mariss

[skullworks]

Originally Posted by Adamj12b So I finished converting my Jet knee mill about 2 weeks ago. ( Snip ) The Z axis one was extremely hot the other night after about 30 mins of running. I almost couldn't touch it. I noticed it when I started to smell it, but I figure Im too late now to save it. I have been looking at buying one of these KL34-180-90 Keling 1125 oz-in servos for the Z and some of the KL34-150-90 for the X and Y when they are needed. The X and Y motor have not even gotten warm yet, but I figure once I start really using the machine they will. ( Snip ) Adam P.S. Here are the motors that you shouldn't get for your machine:http://www.surpluscenter.com/item.as...-2351&catname=

The pic does not really show how you have choosen to drive the knee - but in any case you were sure asking alot from a motor that at proper voltage is about 600 oz-in stall.

As you mentioned above the X/Y motors didn'y get warm - I suspect if you had choosen to drive the quill your Z would have also stayed cool.

[Mariss Freimanis]

A little bit of reality here and an antidote for marketing hype.:-) You do not have a "1125 oz-in servo". You have at best a 200 oz-in servomotor. The 1125 oz-in rating is the peak stall torque of the motor. You use that number and you will burn down the motor and the drive attached to it in 5 minutes.

Look at the motor's "Continuous Stall Torque" rating. Its value will be 0.2 or less of the "Peak Stall Torque" rating. The continuous stall torque rating is the maximum you can use continuously without burning the motor up. Anything above the continuous rating can only be used for very short periods of time (accel, decel, etc).

Motor vendors tout the peak stall torque as if it had practical value. It doesn't (I can't blame Keling, they do it because everyone else does). The only "real" torque you have is the continuous rating. No one touts that because it doesn't look nearly as impressive.:-)

A Z-axis is usually heavy and holds a considerable weight up against gravity. It is a sure-fire and tailor-made axis to destroy a sevomotor unless great care has been taken to insure proper gearing. Use a step motor for the Z-axis. It doesn't care and won't be hurt if it's overloaded. It's smart enough to shed a load it can't carry. People call it stalling like it's a bad thing.:-)

Mariss

[Adamj12b]

All of the axis on my machine are driven with a 4:1 reduction with 3/4" timing pulleys. The X and Y axis are .250 pitch ball-screws, and the Z axis id a .200 pitch stock ACME screw.

Here are a few more pictures of my z axis setup.

Adam