Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Overloaded on August 22, 2008, 07:06:07 PM
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:)
Planning a router table.
Have 3 DC Brush servos.
X and Y motors are: 90v 3400 RPM 4.5A (4 brushes)
Z motor is ............: 48v 2250 4.3 (2)
Will use Gecko's.
To get good performance out of the motors, should I use 2 power supplies ? An 80v and a 50v ?
Gecko says not to exceed 5v over the motor rating. And of course 80v max.
Or...should I use just 1, 48-53v PS for all 3 motors ? The reduced speed on the 90v motors would not be a problem...I hope.
Any advice or alternatives welcome.
RC
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If the reduced speed will not be a problem then just use the one power supply.
Hood
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Will do.
Surprised you didn't jump me for not going AC. ::)
This one is for a friend. (AC's are for me.) ;)
Thanks Hood,
RC 8)
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Nope, if you have DC use them, if you can get DC cheaper than AC use them, If you can get a deal on either DC or AC, AC would be my choice every time :)
I believe in using what suits as well, as an example I made a coil winder for a guy, he was wiling to throw big money at it but I said no point in getting servos so just went with steppers. It doesnt go fast enough or need the accel that servos will give, its never going to lose steps as the steppers are probably 20 times the size needed so didnt see the point in spending 5 to 10 times as much on servos.
Hood
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Read you LOUD and clear !
It's all about the "spending" here.
These motors are new and were all but free.
Twin nut lead screws for now,(free too) maybe ball screws later.
Encoders are now fitted, Gecko's, a power supply and Mach should make a nice set-up.
Will mainly be used for plywood and FRP experimental aircraft parts. Some light gauge aluminum as well.
RC
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Hi, RC & Hood
Gecko's Limit Current to the Amp.value you set them to for Each Drive, Let's say you set them to 4.0 Amps.
At zero speed the current is 4 amps, The Voltage is Low across your servos, As you increase the speed of your servos the voltage increases keeping the current at 4 Amp's.
Theres really no need to use the Lower Voltage Supply.
You Just Need to Limit the Max Speed/Velocity to the Z Axis Motor, To keep from exceeding the 48 volt Max .
Don't Punish the X and Y axises.
Just a Thought, Chip
Hoiod : Spit out that Gum, Get a new piece, You wont need to chew that hard, Your making my Neck Hurt.!!!!!
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Excellent Chip !
So if I limit the Z RPM to 2250 in motor tuning, the higher voltage wont matter ?
GREAT !
Thanks much,
RC
(looks like Hood IS trying to spit it out.........it must be stuck)
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Hi, RC
It's All Brett's Fault, I Think he gave him some "Stride" Gum.!!
Chip
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:D :D :D :D
RC 8)
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What makes you think its gum?.
:D
Its looks more like one of Bretts cigar butts, and looks like he's trying to spit it out
As far as your servos, I'm running 100volt baldor servos on 54 v @ 150" ipm with 340 geckos.
Ed
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Hmmmm. Jethro Tull....Aqualung.
"He bends to pick a dogend"
Is that what I think it is ?
Poor old sod.
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Ha ha
RC
the only thing I would be worried about is that because its not for you the new owner may take it upon himself to crank up the velocity thus increasing the voltage ::o
Hood
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I see what you mean Hood. I'll just make sure that he is well aware.
Thanks,
RC
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Hmmmm. Jethro Tull....Aqualung.
"He bends to pick a dogend"
Is that what I think it is ?
Poor old sod.
You are showing your age now ;D
Hood
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I am pretty sure in a discussion I had with Maurice at Gecko a few years ago he mentioned there was no problem running dc brush type servos at 50% or so higher voltage than the motor rating, something to do with the way the amplifiers work , I know a couple of machines I have worked on in the past (mold handling equip) have had 90vdc motors working with 170+- vdc power supplies.
I know the old bridgeport I am working with came fitted with Reliant 90vdc motors and the original power supply is 177vdc.
I know very little about dc servos and power supplys beyond the basic wiring , just passing along past exp
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RT,
This is what I was referring to...from the gecko manual.
Thanks,
RC
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I am pretty sure in a discussion I had with Maurice at Gecko a few years ago he mentioned there was no problem running dc brush type servos at 50% or so higher voltage than the motor rating, something to do with the way the amplifiers work , I know a couple of machines I have worked on in the past (mold handling equip) have had 90vdc motors working with 170+- vdc power supplies.
I know the old bridgeport I am working with came fitted with Reliant 90vdc motors and the original power supply is 177vdc.
I know very little about dc servos and power supplys beyond the basic wiring , just passing along past exp
That seems like a bad idea to me. With servos, you *want* to be able to run high current briefly, to deal with load changes and accelerations. But, Geckos only have a single current limit adjustment, so it will be active all the time. If you set it to the motors rated current, them you won't be able to get the peak torque to handle transients. If you set it for a reasonable peak current, then if you stall the motors, you'll likely exceed their voltage rating. Mariss indicated to me that the proper thing to do is generally to leave the current limit all the way up, and just use a power supply that is at, or only slightly above, the motors rating.
Regards,
Ray L.