Can someone explain the differences?

[turmite]

I have been following these three threads and would like some help understanding the differences in how these controllers work and what kind of motors they control.


found in servo motors forum:

Poll: New sinusoidal AC servo drive development ( 1 2 3 4 5 ... Last Page )
Xerxes


Sanyo P5 1kw brushless motor spin video
KTP


found in open source controller boards:

DIY Servo controller ( 1 2 3 4 5 ... Last Page )
ejkoeze



Mike

[KTP]

Hi,

I will make an attempt.

"Poll: New sinusoidal AC servo drive development ( 1 2 3 4 5 ... Last Page )
Xerxes "

Very cool idea to develop an open source brushless motor driver (the controller and the power mosfet amplifier on one board) using sinusoidal excitation instead of the simpler-but-possibly-not-as-smooth trapezoidal excitation. Xerxes is leading the design of this board and I believe is nearing the completion of the board layout.

"Sanyo P5 1kw brushless motor spin video
KTP"

My board which is a controller only (no power mosfets) that takes step and direction inputs like the other 2 thread boards (and geckos, etc) and uses a 12 bit DAC and buffer amp to output an analog voltage which is intended to be connected to a separate motor amplifier, such as those made by Copley, AMC, etc. that accept an analog control voltage. My board takes the encoder feedback from the motor, implements a PID algorithm, and commands the amplifier via this control voltage to move the motor to a new position. Obviously you could use either a brush or brushless motor as long as the amplifier supports the type of motor you desire to use.


"DIY Servo controller ( 1 2 3 4 5 ... Last Page )"

This is an interesting project that seems to have started in...Germany?..by a chap named Uli. It is semi-open source, except Uli keeps the code and sells programmed microcontroller chips (for like a beer or something). It is meant for brush motors only. I believe the board is fully through hole devices so it can be soldered by your average hobbyist. It does include the controller and amplifier on the same board.

I believe all three of these devices have their place. I designed the Pixie more for the person who happens to run across a great deal on some commercial motor amplifiers (that are probably going to be a bit more robust than a hobby grade amplifier, simply because a greater amount of engineering time went into the design...usually) or happens to have a cnc machine they are retrofitting that uses amplifiers taking analog control inputs (actually quite common) so they can use their existing amplifiers with the Pixie and save money.

Hope this helped a bit.

[turmite]

Thanks KTP,

Let me see if I understand this correctly.

The "sine" board will control ac brushless??

Your board will control either brush or brushless ac or dc depending on amplifier selection??? I'm not sure about this one!

And Uli's board is for dc brushed motors only, but from what I can gather from the thread with the ability to drive motors with much higher voltages and amperage than say the Gecko's or Rutex??

Close?

Mike

[KTP]

Hi Mike,

Yep, pretty close, except:

The "sine" board will control AC or DC brushless (this is really just how the brushless motor is wound...ones wound to work better with trapezoidal drives are sometimes called DC brushless). Possibly it should be able to drive brush motors as well...Xerxes?

My board is just the "brains" section of a motor driver. It does not care what type of motor is connected to the amplifier, all it wants to do is get feedback in the form of quadrature encoder signals and tell the amplifier to move the motor shaft CW or CCW until the encoder signals agree with the current step count. It does this 10,000 times per second, which is quite a bit higher than the bandwidth of most motors and amplifiers. Got it?

Uli's board is for dc brushed motors...as for how much voltage and current it can drive, that depends on what parts are soldered to the board. Rutex claims some pretty large numbers (200V 40 amps I believe?) for their brush motor amp, so I wouldn't say "much higher voltages and amperage" for the Uli board.

[turmite]

"Got it?" Nooooooo but I'm getting there! The whole purpose for this thread was to find out if it is indeed worth the time and effort for me to roll my own. At present I am more concerned about time and cost management as well as dependability.

After reading all these threads and having this exchange with you I think I will stay with steppers for my next couple of smaller machines. I know the process and how to trouble shoot the sytems. God willing I am planning a big heavy machine as soon as Mach4 is stable with the G-Rex and some of these questions are related to preparing for that. I appreciate your help.

Mike

ps Uli if you read this you're still gonna get a care package! Peppers and seeds!

[Ed_R]

Mike! Did you ever run that guitar?

[KTP]

""Got it?" Nooooooo but I'm getting there!"


Mmmm, I am thinking steppers for you too.

[ger21]

Just to add a little. Mike, most of the brushless designs you see here are to run the Sanyo Denki motors we all bought from Surplus Center. If you didn't get any of those, brushless servos can be very expensive.

I haven't been following the thread on Uli's, but I thought I saw that the main benefit was that it would run bigger motors than Geckos, for example, for a little less money.

Imo, if you get servos that can be run by Gecko's, buy Geckos. It's the quick and easy way.

[KTP]

I will agree with Gary that if you have brush servo motors with reasonably low count encoders, and voltage requirements that don't exceed 80VDC or so go with Geckos. When you get into high rate encoders there could be a bit of a problem with Gecko's fixed 128 counts of position error before faulting(really only a problem on motors with greater than 2500 line encoders I guess). The rutex drives have a bit more flexibility in adjusting the position-error-before-fault variable. Probably Uli's drive does also.


I disagree that brushless servos are more expensive than brush servos...a check at any time on ebay and brushless servos are far cheaper than their brush counterparts for similar torque rated motors. I have a bunch of brush amplifiers I would love to pair with decent (700+ watt) brush servo motors but have been unsuccessful finding a good deal on ebay. OTH, I have purchased about 12 brushless motors on ebay, from 500 to over 1000 watts for around $30 to $70. Most of them were brand new or have seen little use. I believe the average hobbyist is somewhat scared of brushless and so the price is lower....that and there are not as many low cost drive options.

[turmite]

KTP you didn't have to agree so quickly!

Ed I never ran the guitar.??? Pm me or send and email to the non spam address.

ger21 I have been following all these thread with the intent of eventually building that one machine I have wanted for 4 years. I have waited to build it because I can, and the fact that Mariss started the G-Rex project (renamed) and Art is supporting with Mach4. My whole idea is to build a heavy, fast and relative accurate 4 axis carving machine. I know to move the loads I am going to want to move that steppers won't cut it at the speeds I am going to want to move.

Phill Pittman of Masterwerkes down in Dallas was describing to me how fast his machine was and it used small brushless ac servos at 200 vac. I was talking to Art about these one day and he proceeded to tell me he had purchased the same motors and put on one of his small machines. He said you could not believe the speed, torque and smoothness. When he used those three terms he was describing what I want.

When KTP posted his test it literally was music to my ears. Then I went back and begin to re-read the other threads and the confusion set in.

KTP can what you make be used with Xerxes' sine board as the amp, or will amps have to be bought commercially? I actually graduated the USAF school of electronics but it was a long time ago and this is not like riding a bicycle! I guess what I am saying is I can build it, if I have a print, plans or parts. I'm not looking to do anything till I know the G-Rex/Mach4 is stable.

Mike

[Ed_R]

WOnder what kinda money it'll be to build? SOunds pretty powerful.

Mike, I'll email you in a bit.

"Phill Pittman of Masterwerkes down in Dallas..."

Hm... I'm in Dallas. I might have to try and find this guy.

[turmite]

Ed, don't bother trying to find Phill. He has closed shop and is selling commercial lazer scanners! I talked with him late last week and that particular day he was in Florida...I think.

Mike