View Full Version : Hey... I got some servos....

07-30-2003, 11:15 AM
I was cruising ebay yesterday and picked up this little set of servos.


I really only bought them for the 200ppr encoders. I figured that $30 for a set of encoders would be a good deal even if I cant use the motors. But I wonder if the motors would actually be usable... I couldn't find the math to figure out how much power I'd get out of them. I wonder if they'd be as powerful or more so than the steppers that I am runnning. I could not find out any specs on the motors other than they are 23v - 13watt motors.

07-30-2003, 11:17 AM
Lol, I saw those yesterday as I'm after some encoders! I found some others which I will bid on towards closing time though. :D

07-30-2003, 12:14 PM
There are 746 watts in a horsepower. You do the math. I would say they are a great deal for the encoders tho!

Since they are 3000 rpm, if you went belt drive down to 6:1 I am positive they would be more powerful than steppers. A 5 volt, 1 amp unipolar stepper is 10 watts in. they are not 100% efficient so maybe 7 watts out.

If you are buying servo drives anyways, hook em up and check it out!


07-30-2003, 01:04 PM
Yay, I just got some servos too! Sorry for playing this one close to my chest, but I really wanted them! Check them out here (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2547784866&category=1270&rd=1). Balsaman, the other servos which I was testing seemed ok, but after i found these, I thought I'd keep the others as spares. After all, a big 24v PSU will be easier to find than a big 80v too.

07-30-2003, 01:17 PM
Well that works out to be...

0.0174263 hp

23 V
0.57 A
40 ohms

how does gearing down affect torque. (I know it increases but at what ratio?) lets say you had 1lb of torque and you geared that 2:1 does that give you 2lbs of torque or is it a bit more complex than that?

I'm currently using 16tpi threaded rod. until I can bone up for real screws. Gearing down 6:1 would give me a max of only 31.25ipm.

6:1 = 500rpm / 16tpi = 31.25 ipm

3:1 = 1000rpm / 16tpi = 62 ipm

2:1 = 1500rpm / 16tpi = 93.75 ipm

So until I do a leadscrew upgrade. only a 2:1 would give me any real speed increase as I can jog almost 50 ipm with my current stepper setup. I don't know how that .0174hp would translate into actual force.

and yes I've almost convinced myself to go ahead and buy some Geckos in anticipation of going servo. I might just go ahead and pick up one to mess with until I get the motor situation together.

07-30-2003, 01:34 PM
The torque multiplication is exactly like you wrote it, at the expense of speed; 2:1 ratio doubles the torque and halves the speed. Less a little for friction of course.

robotic regards,


07-30-2003, 01:44 PM
Since you are using 16 tpi rod, you can get away with less reduction, because the rod itself is a reduction, like a shallow inclined plane.

Buy a gecko and bolt it on!


07-30-2003, 02:10 PM
Kong, those servos will need an external encoder. Good price!


07-30-2003, 02:13 PM
Originally posted by kong
Lol, I saw those yesterday as I'm after some encoders! I found some others which I will bid on towards closing time though. :D
I'm on the case!
Ok, at the risk of someone else getting them, I'm currently watching these (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2547651986&category=4677&rd=1)

07-30-2003, 02:24 PM
F-it I just ordered 3 geckos.... (I needed to put the child tax credit check to use somewhere.... ) :D

Now.... I need everyone to be on the lookout for a killer deal on a set of "real" servos... I've already pushed the "Toys" budget for the next month or two. So killer deals only need apply.... (I know some of you guys are hoarding dozens of these things away greedily and can spare 3. ;) )

I'll give these little Hitachi motors a spin and see what happens. I'm still not terribly optimistic though. But then again it might be suprising. I know that my 14v cordless drill will send any of my axis flying with very little effort. and I'm suing UMHW slides on aluminum channel currently. There will be much less force required when I upgrade to real linear bearings in the next few weeks.

07-30-2003, 02:31 PM
Mate, I'd offer my spares, but a) I don't know what kind of torque they are putting out and b) I live about 2000 miles away in UK so the postage would be about $1Million. Just keep holding out for that ebay deal and they will turn up, they have for me.

07-30-2003, 03:10 PM

I just got hold of 6 of those. They're pretty chunky beasts but should be great for our needs. As for encoders you may want to check out farnell. They've got some solid state hewlett packard encoders for about 30 each which are perfect for the above. 5V and 17mA supply, quadrature units which should be just right for interfacing to Geckos. It's great to see useful lots appearing this side of the water. The guys over in the US don't know how lucky they are getting all the good deals. I've just ordered some THK linear rails and carriages from a chap in the states - the units were a very good price but the shipping was the best part of 200!

07-30-2003, 03:23 PM
The US getting all the good deals, you got that right! I think the servos are the only part of my planned machine to come from the UK, and on my current machine, the steppers and driver board were both american! As for farnell, well I hate paying full price for anything so I'm keeping my eyes on ebay. Don't suppose you know of anywhere to get some cheap linear shafting do you? Cheapest I have found is RS electronics.

07-30-2003, 04:31 PM
I saw that shafting on RS myself. It's SKF unless I'm mistaken. It's actually at a very good price. You can certainly get cheaper elsewhere but it won't be of the same standard. It all depends on what bearings you're planning on using on the shafts and the load they'll be carrying. If you're using plain bearings or oilite bushings then you can probably get away with unhardened shafting or even drill rod but if you're planning on using linear ball bearings then you'll need something hardened otherwise it will wear very quickly. I'm a little biased towards SKF as I worked for them a couple of years ago - I wish I still did - my current machine would have been half the cost nevermind, anyway that shafting is manufactured in a small town called Hofors in the middle of nowhere over in Sweden. They produce some of the best steel in the world over there. SKF's components are rarely the cheapest but most in the industry would agree that they're without doubt of the highest quality. I think RS have also got the SKF compact linear bearings for 16mm shaft at about 10 each which seems pretty reasonable. I don't know if you've had a look at www.ondrives.com, they've got some useful kit as well. What are you planning on using your new machine for? Have you decided on a spindle yet. I've noticed that a lot of guys on this forum have opted for either Porter Cable or Makita routers, both of which seem very capable. Unfortunately over here the only Makita models you can get are designed fo hand use only and as such have that unsightly plastic molding that makes it almost impossible to mount. I'm thinking of buying a Makita RF1101 from the states and making a 110V supply to run it off. Does anyone know of a speed controller for such a router, something that could be driven from turbocnc or mach2 for example. Balsaman I see that you used a speed controller for your latest machine, was that homemade or bought in?

07-30-2003, 05:12 PM
The spindle I have at the moment is a B&Q "pro performace" fixed head router. It is the only American style router I have seen over here. Not a bad unit, 1250w, 1/2" collet, and possibly the poorest quality 15 piece cutter set you're likely to find, but for 52, a bargain.

07-31-2003, 12:26 AM
My speed control came from a vibrating table (like a conveyor that shakes the parts along). I had to fix it. All it does is vary the ac voltage to the shaker unit which is just what you need to vary a routers speed. It works like a charm. It's just a circuit board.

Ones made just for routers can easily be found on ebay for $30.00. They have the plugs and everything.


07-31-2003, 01:55 AM

I came across a box at work a couple of weeks ago stuffed in the maintenence room by itself. It has a big knob on it and it says variable speed something or other. On the knob I think it said Ohmite or something. It had what looked like a standard 3 prong drounded AC outlet on it.

After reading your post, Im wondering about this box. It had no other markings on it.

Ever hear of anything like that ?


edit: I did some searching and Im thinking it is a Variable AC transformer. I will chack it out tomorrow. Is this what you are describing for speed control for your router.

07-31-2003, 02:04 AM
It's probably some kind of variable resistor. If it's very large, it might work, but it will get hot. That's how they used to do it.


07-31-2003, 12:27 PM

It is a variable speed control (for what I dont know).
It says it is an variable AC transformer.
It is rated 120 V, 5.6 A. The routers I was considering were 10 amp models.

Sorry for hijacking the thread.

07-31-2003, 01:48 PM
Back to these encoders, are these going to work with Geckos? I am asking because I was just about to bid on the ones I mentioned earlier, but then I noticed an extra $15 admin charg for international orders! Also, I notice the ones you have are magnetic encoders and as I have not had time to check them out, I thought I'd check first as there are some more on ebay.

07-31-2003, 03:55 PM
I'm not sure that the Geckos really care how the encoder pulses are generated, just as long as it gets them. Won't know for sure until I (A) try it or (B) Ask the guys at Gecko....

07-31-2003, 08:39 PM
For a cheapish manual router speed control maybe look at;

08-01-2003, 02:34 PM
CAMmando: sounds like you might have a "Variac". As I understand it, "router speed controls" only work for universal motors (like in a router), whereas a variac would work for an induction motor.

/me returns to lurking.

08-06-2003, 08:22 AM

I was wondering whether you'd decided on some encoders and drivers for the servos. I plan on using geckos and those hp encoders from farnell i mentioned but am in the process of moving house at the moment so my cnc build has had to be shelved for the next couple of weeks. Let me know when you get the motors fired up - I'm curious what kind of performance we're likely to get out of them! Happy tinkering.

08-06-2003, 09:06 AM
Damn it, I just got in from work and thers a little note through the door to say i missed the delivery man and he'll be back tomorrow! I have however picked up a nice 24v 25Amp PSU on ebay for 30 to drive them, and i will be using geckos, but can't afford them yet. As for the encoders, I'm waiting to see if the ones Anoel bought on ebay are gonna be ok, coz there are some more there. If not, I posted a link to an ebay auction further up this thread for 4 optical encoders for $25 + p&p which I shall probably go with. They are 200 cpr i think, and 5v, digital quad out, so just right for the geckos. There are more on ebay if you hunt around. i have still got to get my linear bearing shaft, and ballscrews yet, so I'm a long way behind you in the building stages - I'm aiming for christmas to be honest. Just found a lovely scrap yard in Southampton, lots of practically new 12mm aluminium plate for 2/Kg. I bought a load last week, and will get the rest shortly. If you have started building, it would be nice to get a new thread on the go!

08-06-2003, 10:41 AM
Kong, I got those little motors the other day. Of course they are too small to use. :)

But I did pop open the encoder on one of them and it looks to be a nice precision encoder. The wheel is laser cut and looks to be a standard mounting. My Geckos have shipped and I should get them in the next day or two. I'll have to whip up a little breadboard circuit to get step/dir form the computer and wire up a test to see if those encoders will work out. The shaft mount for the encoder wheel is a press fit bronze bushing. so I think I can bore it out to fit a larger shaft without too much problem.

Again I just bought these incase I ran across a good deal on motors that did not have encoders already. If I don't get to use them I'm not out any real money.

I'll report back on them when I'm able to test them.