Have almost all my parts (pics), need servo advice

[Darren_T]

I finally have all my linear motion rails/bearings and have all the aluminum I need to begin building my CNC Router. I think I've talked myself into going with servos instead of steppers. I'll be using this machine for more than I had originally anticipated so I want it to mill aluminum without struggling.

My dillema? I know nothing about servo motors or driver boards etc... I'm a quick study and have no problems assembling electronic equipment, I just need some advice from those with experience.

What size servo's would you recommend? I'm assuming I'll be buying Gecko's driver boards but am not sure which model... of course I know it will depend on the servos etc...

I've found the servo's below, what do you think?

Below are some random statments from the seller's description:
>>>
Electro-craft DC brush type servo motors Model E540. Shaft is 5/16 dia with a small pulley at the end. Remove the pulley and the shaft has been machined down to 1/4 inch for about 5/8 inch. Encoders are BEI MOD56-551 and look just like the HP Heds series. unable to determine encoder resolution but I believe them to be at least 250 CPR. I've been running a set with Gecko G320 drives and they perform great. 240 in oz peak torque. Quadrature operation, 5 vdc 35 ma. 24-28 vdc 3770 RPM.
<<<

240oz/in isn't terribly strong for a servo from what I've seen but more than twice the torque of the steppers I was considering.

I appreciate everyone's help on this. I intend to begin my build over my xmas vacation and will definately take pics and document my experience for those who are interested.

Any recommendations? I'm trying to keep the servos and driver boards within a $500 budget. That would put my machine costs at around $750 since I got all my aluminum free. It would also keep my wife happy I know, that's gonna be tight. The Gecko's alone will be more than $350... doesn't leave much for Servos. Oh, is there good free software that will run servo's well? I noticed on the Gecko website they say with the G320 you can run the servo's with stepper software.

Darren

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[Darren_T]

Here are some pics of my rails/bearings acquired from ebay. I got everything I needed for less than $250 shipped. If ya keep on those auctions you sure can get some good stuff for a steal!


Z axis (3/4" X 18" supported)

Z axis 2

Z axis 3

Y axis (double 1/2" rail x 36")

y axis 2

x axis (3/4" X 24")

[balsaman]

I think Jeff (HomeCnc) had some nice servo's with encoders for $75.00 each in the for sale forum.

Turbocnc will run your servo's fine at $20.00 to register.

[Darren_T]

Originally posted by balsaman
I think Jeff (HomeCnc) had some nice servo's with encoders for $75.00 each in the for sale forum.

Turbocnc will run your servo's fine at $20.00 to register.

That sounds perfect. I'll look into that. Turbocnc sounds perfect. I'm trying to get it working for as little money as possible but don't want to skimp... probalby what 90% of the people are doing I suppose I'll check those out.

[EDIT]

Just checked them out and think I'm going to buy three. Which acme thread pitch would you recommend with those motors? 10 tpi?

Thanks again.

Darren

[kong]

I'm running 350 oz/in servos on my ali machine, with a 1:1.5 reduction, they have awesome power. Good choice.
My screws are about 5.5Tpi (poor metric conversion, sorry), perhaps 10tpi is a little fine for those servos?

[buscht]

Darren, don't forget about the power supply, fan, heatsinks, enclosure box, wiring, switches, etc. in your budgeting.

[Darren_T]

Originally posted by buscht
Darren, don't forget about the power supply, fan, heatsinks, enclosure box, wiring, switches, etc. in your budgeting.

Yup, I'm not counting the smaller ticket items as I can slip purchases like that by the wife without raising an eyebrow I have a case and plenty of wiring left over from computer parts and fans. I'll still need to get heatsinks, switches, power supply, and a few other things though

Thanks for the info. I'm still not sure of absolutely everything I'll need... I'm sure there will be a surprise or two. Hey, is there an article or anything I can read to figure out EVERYTHING I'll be needing? That would be great. I still don't know all the smaller misc. items I'll be needing.

Darren

[HomeCNC]

Making a servo controller box is not that cheap! Be careful about this. Look at my website, I have a picture of a servo controller box that I built for someone on the Zone. It was about $800 just for all the parts. Geckos were part of that cost.

[Darren_T]

Originally posted by HomeCNC
Making a servo controller box is not that cheap! Be careful about this. Look at my website, I have a picture of a servo controller box that I built for someone on the Zone. It was about $800 just for all the parts. Geckos were part of that cost.

OUCH!!! I guess I'm a bit naive about the cost of this. I'm looking at the box you built. I see a torroid, cap, 3 gecko's, and another board hooked to the gecko's. What is that board? A break-out? I'm still learning. I can't be spending $800 on a servo control box.

[buscht]

Darren, some other things that you haven't mentioned are the lead screws that you want to use, I'm guessing that these could cost anywhere from $25 to $100 per axis. Framework could run another $200

[Darren_T]

Originally posted by buscht
Darren, some other things that you haven't mentioned are the lead screws that you want to use, I'm guessing that these could cost anywhere from $25 to $100 per axis. Framework could run another $200

I have all the aluminum I could ever want and I figure my lead screws being acme screws will be no more than $20 per axis. I plan to make my own anti-backlash nuts etc...

Why does the servo control box cost $800 to build? What am I missing???

3 Gecko's = $350ish
Power Supply = $50?
Heat sync's = ??
Misc. Cables = next to nothing

What else?

[ger21]

I would think a good power supply is more like $150-$200. Breakout board = $125
Decent cables can be a lot more than nothing.
That box on Jeff's site has a pretty nice case, more $$.

Gerry

[sol]

It does not have to cost that much if you just want the thing to work...bells and whistles can come later.
Mine was around $500
$125 for power supply (toroid, cap, rectifier, resistors)
Three Gecko 320s $350.
Printer cable hooked to terminal strips $10?
No need for a breakout board....
Three push button switches from Radioshack for Gecko reset $2
Main power switch with box $2 (15 amp wall switch and handy box)
Cut up 12 ga. extension cord for servo power cords
cat5 wire for encoders
My Geckos barely get warm, no heat sink, just spaced with washers above the mounting board.
The rectifier's "heat sink" is a piece of thin aluminum (soda can) which steps it above the board and it does not get warm either.
Yeah, if money were not an issue these beautiful products that are shared here at the Zone would be real nice, but meanwhile back on Earth there is tuition for the kid and insurance and........

[Darren]

Originally posted by sol
It does not have to cost that much if you just want the thing to work...bells and whistles can come later.
Mine was around $500
$125 for power supply (toroid, cap, rectifier, resistors)
Three Gecko 320s $350.
Printer cable hooked to terminal strips $10?
No need for a breakout board....
Three push button switches from Radioshack for Gecko reset $2
Main power switch with box $2 (15 amp wall switch and handy box)
Cut up 12 ga. extension cord for servo power cords
cat5 wire for encoders
My Geckos barely get warm, no heat sink, just spaced with washers above the mounting board.
The rectifier's "heat sink" is a piece of thin aluminum (soda can) which steps it above the board and it does not get warm either.
Yeah, if money were not an issue these beautiful products that are shared here at the Zone would be real nice, but meanwhile back on Earth there is tuition for the kid and insurance and........

There we go. This is more like it. I have a case, no need for heat syncs if you have aluminum of your own...I can make some easy. Cables are cheap and the break out board is only for limit switches right? No need right away for that. I can always do those later.

Phew, thought I was going insane there for a minute. We went from DIY to retail.

One question. Why are people using expensive toroids for their power supplies?

Darren

[sol]

Higher amperage
Plitron's toroids have two sets of outputs; that is they are essentially two transformers in one; wire the outputs in parallel and double the amperage...they run around $80, but shipping takes another $20...they're a heavy spool of copper.

[Darren_T]

Ah, makes perfect sense. I've built 3 power supplies with the toroids but it was for a home theater amplifier that I assembled. I don't know much about electronics but I can assemble with the best of em

Thanks for the info.

Darren

[barbwirebi]

Darren

I also am trying to build a controler box to power the same motors
that Jeff is selling.
I also need to keep cost's down.
Have you located the toroids yet? I am tring to find them.
Please continue to post your progress on building this box
I think it could help alot of us.
Sol thanks a ton for the help

Bill

[HomeCNC]

The toroid was purchased from www.plitron.com It is in fact two transformers in one. This is one reason why I like them. If you purchase the 10 amp 25VAC output it will convert to a nice 36VDC 20 amp supply. If you get the 15 amp toroid you can have a 30 amp supply. Remember, the larger the amps you go, the larger the Cap must be. (more money!)

There are places to cut costs, but be careful. On my first servo controller box I made my own encoder cables. One cable must have been not quite up-to-par. Everything worked fine for a while. All of a sudden one connection on the encoder must have disconnected. When this happens the servo motor turns back into a DC motor, and you have the full DC volts applied to it. It starting running at FULL RPM. I had to hit the power switch before my table slammed into the stop. I now purchase proper encoder cables from USDigital.

Like someone said. It's all in the bells and whistles (or quality) you can afford.

[Bloy2004]

Jeff! I can imagine your panic motivated leap to cut the power!
Have you heard of any other stories about home machines with servos running away? I have a shoptask metal lathe fitted with servos and intend on installing limit switches, but I worry about the inertia carrying the force through and doing damage.

[balsaman]

Doing damage to what? The limit switches or the lathe?

Install the limits so the axis can travel by them without damage. Make sure there is room after the limits for things to stop without crashing into something.

Eric