Good source for inexpensive servos?

[rcnewcomb]

I'm assisting a high school student with a robotics project. I'll be meeting him for the first time later this week. He is trying to build a robotic arm. He's trying to keep the project under $200. One of the challenges he is running into is finding a source for inexpensive servos. Does anyone have suggestions on where to find lighter duty servo motors that might be useful in this application?

[myxpykalix]

i'm not sure what might be inexpensive when it comes to robotics so here are these:
http://www.solarbotics.com/
http://www.pololu.com/
http://www.micromark.com/Motorized-Planetary-Gearbox,8179.html

[steve_g]

http://www.mpja.com/Stepper-Motors/products/101/

[myxpykalix]

Steve
have you bought motors from them before? If one was going to do some geared kinetic sculptures what would be the best motor to buy? Also what is best power supply and switches?

[steve_g]

Jack...

I've bought quite a bit from these folks over the years, not servos however. One problem I have had with these folks is that I'll do prototype design with their products, get an approval on a design... production quantities are not available. Use them for proof of concept or just for fun!

Steve

Some day I want to make a clock that uses servos and a microprocessor... I want It to randomly spin crazily then stop at the correct time...

[myxpykalix]

so do you have any recommendations on particular motors? For example, i don't know the difference between

24V, .16A, 3.6 Deg. NEMA 14 Step Motor
or
5.2V,1A,1.8 Deg. NEMA 17 Step Motor

so i don't really know what voltage to buy, what the degree designation means or the difference between 14 or 17 step? I guess that means 14 steps within a 360 rotation?

[steve_g]

http://www.mpja.com/12VDC-68-RPM-Gearhead-Motor/productinfo/15870+MD/ (http://www.mpja.com/12VDC-68-RPM-Gearhead-Motor/productinfo/15870+MD/)

I'll bet this motor will have a lot of torque and work well for a beginning kinetic sculpture. Plus the 12VDC will be a very common Power supply. It's not a stepper, just a DC motor.

Steve

http://www.mpja.com/12VDC-2A-Regulated-Plug-Supply-Jasper/productinfo/18776+PS/

this power supply has about 2X the current necessary to drive the motor

[steve_g]

i don't know the difference between 24V, .16A, 3.6 Deg. NEMA 14 Step Motor or 5.2V,1A,1.8 Deg. NEMA 17 Step Motor




Jack

Stepper motors, like the ones on a ShopBot can be controlled very precisely. It moves a step for every pulse given by a control source... like a computer. A DC (direct current) motor can be adjusted speed-wise with varying amounts of voltage and can be reversed by reversing the polarity of the power source. The NEMA # is a standard size designation common to all manufactures. The degree designation is how much the motor rotates for every step... then you get involved with 1/4 and 1/2 steppers etc.

For a beginning kinetic sculpture, all the electronics that would be involved in getting a stepper to power it is out of the scope of a "simple" project. Unless that is if you are really into the electronics part of it.

I'm sure I have grossly simplified this explanation, but the nice thing about this forum, someone will graciously correct any maters of fact!

Steve

[myxpykalix]

I figure all i need for a first project is a simple motor to just rotate everything. I wasn't sure if their term of "stepper motor" was the same as what we know and use. At some point like you say if some design calls for irratic movement then those may come into play.

I have some ideas for sculpture elements but i will post those thoughts back in the gear making post.:eek:

thanks for the links

[myxpykalix]

I ordered 2 motors 2 power supplies we'll see how it works when they get here..

[Brady Watson]

I'm assisting a high school student with a robotics project. I'll be meeting him for the first time later this week. He is trying to build a robotic arm. He's trying to keep the project under $200. One of the challenges he is running into is finding a source for inexpensive servos. Does anyone have suggestions on where to find lighter duty servo motors that might be useful in this application?

What kind of servos?

1) Small, cheap, mass-produced actuators used for radio control and small robotics, controlled by PWM to vary position, typically 5-12VDC.

2) A standard 3ph AC or DC motor coupled with an encoder and drive/amplifier that typically takes step & direction commands to control position.

Two totally different animals...The first of which would be most appropriate for a robotic arm, since it will have more holding torque than a comparable 2nd one pound for pound.

-B

[cabnet636]

try pitsco

http://www.pitsco.com/

[hh_woodworking]

An other source :http://www.kelvin.com/ or electronix express is very good and carries some over runs cheap at times http://elexp.com/on_web.htm

[Brady Watson]

What kind of servos?

1) Small, cheap, mass-produced actuators used for radio control and small robotics, controlled by PWM to vary position, typically 5-12VDC.

2) A standard 3ph AC or DC motor coupled with an encoder and drive/amplifier that typically takes step & direction commands to control position.

Two totally different animals...The first of which would be most appropriate for a robotic arm, since it will have more holding torque than a comparable 2nd one pound for pound.

Again....What KIND of servos?

-B

[dana_swift]

Check with www.sparkfun.com and other such sources, you can get them for under $10. It depends on what you want. If you want something that moves and precision or force capacity is not a big issue, you can find some really inexpensive ones. You can find some very impressive capability in some models built for the micro-robotics industry. They often stop being cheap tho.

An R/C "actuator" is a genuine servo according to definition #2: "2) A standard 3ph AC or DC motor coupled with an encoder and drive/amplifier that typically takes step & direction commands to control position."

In fact: All R/C servo "actuators" contain a DC motor coupled with an encoder and a drive/amplifier that takes precision position commands and moves the output shaft to the required position within its rated precision and torque capability. They are servos in every sense of the word, and its why they are called that.

R/C Servos come in all flavors, sizes and capacities, they are all designed to run on nominal 4.8v power contrary to an earlier post. The exact max and min power requirements are manufacturer dependent, but all of them will run at 4.8v. I have worked with R/C servos that required two power supplies, a 4.8 for the control electronics, and a higher voltage (12-24) high current for the motor driver. They look almost identical to the little feeble ones.

Some of the newer generation of R/C servos accept serial data from a cpu and allow control over position, speed, and torque. All in a case that looks like a traditional R/C digital-proportional servo. Some of these newer models could be used in novel shopbot applications. The older ones would be useful for where pneumatics are used now.

These small servos that were originally intended for only the R/C market have spread to many new and novel applications. Kind of like what happened in the CNC world due to the availability of high performance/low cost stepper motor systems.

Randall- if you want any more specific info, pm me.

Hope that helps!

D

[rcboats1]

www.servocity.com

[rcnewcomb]

Again....What KIND of servos?

-B

based on the $200 price limit for the entire project the choice seems to be:

1) Small, cheap, mass-produced actuators used for radio control and small robotics, controlled by PWM to vary position, typically 5-12VDC.

[Brady Watson]

Arduino + 'Servo Shield' + Servos + Power Pack = 1,000,001 possibilities...

...and probably less than $100 for everything + whatever structural materials you need.

-B

[rcnewcomb]

Arduino + 'Servo Shield' + Servos + Power Pack = 1,000,001 possibilities...

This was a great suggestion. Through meetup.org I found some groups that use Arduino and looked at some working examples this past weekend. Once guy had built several tiny machines with this setup that he was able to demonstrate and explain.

[rcnewcomb]

I wanted to thank Brady for suggesting arduino for this project.

We ultimately decided to hack an arduino (http://www.arduino.cc/) interface onto an OWI robotic arm (http://www.owirobots.com/cart/catalog/OWI-535-ROBOTIC-ARM-EDGE-KIT-87.html).

We were able to do the project for well under his $200 limit.

The OWI arm comes completely unassembled. Putting it together helped the student understand how each joint and motor combination operated

While the Arduino Uno board came fully assembled the motor shield was just a PC board, components, and instructions on how to solder the components onto the circuit board.

He also got to figure out how to write the program to control the arm.

He hooked 4 of the 5 motors to the interface. He was programming it to pick up a block and move it to a new location. He was making good progress on the software but, alas, at 4AM the day of the presentation the motor shield failed. We haven't done a failure analysis yet, but I'm sure it will be an easy fix.

All in all he learned a lot on this project and most everything will be reusable for subsequent projects. We've already discussed how to improve the design of the arm.

He's is very bright and hard-working. He'll make a great engineer. I truly enjoyed helping with this project.

Brady, thanks again for your suggestion.

[Brady Watson]

Randy,
No problem - glad I could help out.

That's a bummer about the shield going out the night before the show. Hopefully there were all kinds of lessons learned - because (as you probably know) these things happen all the time in the real world!

-B

[rcnewcomb]

because (as you probably know) these things happen all the time in the real world!

We had talked about that the week before. It had never occurred to him that there might be problems. I'm glad we had the discussion because this way, when there were issues, he didn't freak out or become completely disillusioned (though understandably disappointed).

[myxpykalix]

This thread and discussion kind of reminds me of some question I had asked several years ago (forgot what it was) and a guy who rarely contributed chimed in and basically said "figure it out for yourself!"...

I wish i could recall the D-bags name..anyway to my point, this is a prime example of others sharing their knowledge and experience which helps others not have to waste time or material making mistakes that someone already has. So although i am not going to be building a robot anytime soon i can still learn something from most all posts. So thanks for your contributions guys..:D

[steve_g]

Soooo.... did ya figure it out, Jack?

[rcnewcomb]

I was pretty impressed with the capabilities of the Arduino boards. If you need a basic controller for digital or analog it seems to have a lot of bang for the buck. The software is free and runs on a variety of platforms. I tested it on both Win7 and Mac OSX. Once the board is programmed it doesn't have to stay connected to a computer -- it just needs a different power source.

For $16 you can get a board which has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, etc. It contains everything needed to support the microcontroller; you can connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery.

For $47 you can get a board that has 54 digital input/output pins (of which 14 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button.

At a Meetup recently there was a guy building very basic CNC machines using an Arduino controller that could accept G code. Certainly no replacement for a ShopBot, but a good tool for learning about CNC machines.

Go to YouTube and search for Arduino. You'll be amazed at the variety of things people are doing with these boards.

[myxpykalix]

Soooo.... did ya figure it out, Jack?

Obviously not....or I wouldn't be asking....Figure what out?:confused::D

[steve_g]

a guy who rarely contributed chimed in and basically said "figure it out for yourself!"...


Sooo you never did remember what it was you wanted to figure out.???

[dana_swift]

Arduinos are the center of a whole world of do-it-yourself tinkerers. Arduino people are very much like shopbot people in delighting in finding new applications and techniques to use with their devices.

Its a tool available for very little money, try something, if it doesnt work, try something else. Usually you don't damage the device, even if you do a working adult can usually handle the replacement costs.

I have suggested that Shopbotters would benefit to be familiar with them. Its a different kind of tool, but well worth exploring if it looks interesting. Not everybody will want to, just like some Arduino users will not be interested in Shopbots, they would benefit from knowing more about the power of our robust low cost tools.

Having a shopbot is really great, where we have an advantage over most of the arduino users is that we have these incredible manufacturing ability for special cases, gears, linkages, mounts, etc.

Randall I am glad you both had such a positive experience with them, and hope to hear of other projects and fun stuff you do with them.

D

[myxpykalix]

Dana,
I'm not much of an electronics guy and i've read all of the things you've written and it seems like you know what you are talking about, so let me ask you...
In another thread about gearmaking it went into buying certain servo motors and things and i'm wondering if this Arduino isn't something you could use in conjunction with these servo motors to program different movements? What i mean is, rather then having a gear set just go clockwise could you use something like this to program say (X)minutes of clockwise movement, then (X) minutes of counterclockwise movement, and just random things like that?

Is this something like a small chip that you plug in (someway) and have some type of interface where you program certain instructions?:confused:

[myxpykalix]

Steve,
That was years ago, and i think my response was something along the lines of.."this is a forum where you ask for and receive help in order to keep you from making mistakes and wasting time and resources"...i don't think he has bothered to post since then. So now that i am getting close to 4850 posts, i've tried to repay all those who helped me when i was a newbie by helping others.:D

[dana_swift]

Jack- the arduino can be connected to almost anything to do almost any task you can imagine. Its not a high power computer for $30. But its inexpensive enough to dedicate to a single application.

http://arduino.cc/

These devices do not need to be loaded with a program each time they are run. Until you send one a new task, they do the last one any time they have power on.

You could implement your motor concept like you describe, although most R/C servos have a normal turn range of +/- 30 degrees, others allow many turns from one stop to the other. A better way is stepper motors, which are often used with the arduino also.

The arduino is a circuit board that plugs into your PC using a USB cable. When its hooked to your computer the USB cable provides power for the arduino and associated circuits. When you have it working the way you want it to, it also has a round power connector you can plug into a "wall wart" power adapter, or a battery. When the power goes on, the arduino immediately starts doing whatever list of instructions it was last told to do.

The arduiinos have two rows of pin socket connectors on 0.1" centers. For quickly hooking the arduino to an led, or switch, most folks just jab a wire into the socket and check to see if what they want to do will work. Spend no extra money.

For a long-term application expect to buy one or more "shields" which is another circuit board that covers the top of the arduino. Shields can do anything from provide internet access, to stepper motor drivers, and of course give you a place to properly terminate those wires that used to be just jabbed into the sockets so they wont come loose under real use.

Jack, you mentioned not being an electronics guy. Most arduino users are not electronics guys either. Somewhat like the shopbot. Shopbot people are not usually "programmers" either, but after owning a bot for a while we all seem to learn what C3 means, as well as Z2, C2, MX, etc. We are programming and controlling the shopbot whether we think of it that way or not.

The arduinos have their own language like the shopbot has. It is designed to make it easy to understand what you are wanting the arduino to do, just like SBC commands dont take long to figure out.

A person facing the shopbot for the first time may seem overwhelmed by all the commands. You end up just using a few of them all the time. Same thing with the arduino. You can use a mac, pc or linux to set the arduino up. Here is their "getting started" pages:

http://arduino.cc/en/Guide/HomePage
http://arduino.cc/en/Tutorial/HomePage

From the tutorial on how to make an LED blink, Arduino commands look like:
pinMode(13, OUTPUT);

That tells the arduino pin number 13 is an output. It may not be any easier to remember than C3 was at first, but at least you can read it and make a good guess at what it does.

For $30, get one and do something simple like make an led blink. Then have two led's and have them alternate. Try four, and have them sequence. You will get the hang of it pretty quickly. Just like the shopbot.

Then think.. the shobot has about 4 spare inputs and outputs. So does the arduino. So now you have the ability to use the two together.

For a shopbot application.. have the shopbot set an output to indicate when you want your dust collection system and vacuum hold-down to come on. Not a good idea to start them both at once, so have the arduino convert one "on" into two time delayed on commands to start hold down followed by dust collection. If the shopbot signals "off" turn them both off at the same time.

To do that, it would take an arduino, a shield to drive contactors which would control the motors. And an enclosure you could build easily with the bot, mount it somewhere appropriate.

Then consider, that the vacuum level drops too much to safely hold the parts down. You could have the arduino automatically kick in a backup fein, or whatever.

I think/dream in terms of automated material loading/unloading from the bot. And who knows what other ideas may come.

Arduinos are similar to shobots in that once you do something better than you thought you could, you find yourself thinking of other things you can do with them.

Your imagination, persistence, and curiosity set the limits.

Just like with the bot.

Enjoy, more cool stuff to employ in using your bot.

D

[myxpykalix]

thanks dana i'll read up on those links. I have to start thinking in terms of doing smaller tasks due to arm issues so this might be worth looking into.:D