Selecting Components for DIY Robotic Arm

**tikka308** · 06-01-2010

Hi folks. By way of introduction, I am a machinist (www.nyccnc.com) who would like to construct a DIY robotic arm. The reason for my post is that I only have a beginners understanding of electronics (e.g. lots of Arduino tinkering) and am seeking initial guidance on the components. My goal is to build an arm which is MORE similar to those you see by Denso, Kuka, ABB, etc versus the DIY-servo inside each joint. My thought is to use timing pulleys as seen here (http://www.strikemark.com/HowItsMade.jpg) from How Its Made which will allow heavy servo motors (or DC motors?) to reside in the base of the arm.

I have no specific goal with regard to lifting capacity. I would, however, like the robotic arm to function very smoothly. I would expect to spend $1,000 to $1,500 on the project (excluding all raw materials and machining, since I have those capabilities in-house).

My first step is to start tinkering with a base system and the first joint. Since I want beefier and smoother set up, I know I need something with higher current and more advanced control than Arduino (which is the only system I've worked with). Per Trossen's youtube video on motor controllers (http://www.youtube.com/watch?v=X4stWDy-bPA), it looks like I'll need a servo controller (for PWM?), DC motor controller and motor (DC Gear or servo?). I'd also like an encoder and encoder reader. This is where I would love some guidance from folks more experienced than I. Could someone please suggest a set of products from Trossen so that I can start experimenting and learning? I saw the Phidget family of products - is that something you would recommend?

If I can be of assistance to anyone seeking advice, tips, etc re: CNC machining, manual lathe work, sheet metal, etc - please don't hesitate to reach out.

zoomkat · 06-01-2010

If you want to do something bigger than usual, make the below digger as an arm. Could use the same basic setup as a big servo arm.

http://www.firgelliauto.com/robotics...s-projects.php

**Al1970** · 06-02-2010

Hi:

Hobby type servos would NOT work for what you want to do. You have to make the servo free running. Which can be a pain. There are some that are free running but not many and the motor inside are small. Industrial type servos would cost you an arm and a leg (Ha Ha). So I would go with DC motors. So you need a DC motor controller. An encoder wheel for feedback. A H-bridge and some power. I can't help you to pick out trossen parts since I build all that electronic stuff myself.

You really do need some idea of how much you want the arm to lift, in order to buy the parts. Bigger motors means more watts which means, H-bridges that can take more watts.

Al

**tikka308** · 06-02-2010

Very helpful - so DC motors with encoder wheels it is. I haven't nailed down the details of the arm yet because I just want to first experiment with one joint. So while I cannot say exactly how much weight (nor DoF) I'll want, I'll throw out an example of 3 DoF (like this http://www.societyofrobots.com/image...t_arm_arm3.jpg) and the ability to lift 2 lbs and a total reach of 24".

**Al1970** · 06-03-2010

Hi tikka308:

I am not a machinist. So I have to buy ready made parts. I tried making motor in joints human type arms. I also tried motors in base belt human type arm. As soon as you try to get a good long reach, the motors needed, become really big.

Here a small (have plans to make a more powerfully arm some day) see if idea works type. It alot more practical not to base it on a human type arm. It some what like a forklift. The base of the robot gives the arm 2 DOF. So a total of 5 small motors is all that was needed. The arm can move a object as big as a glass vase 45" in the air. The total cost of all the motors used was only $50. You could never do that with a human type model for that cost.

http://diyrobots.webng.com/VideoP/VideoP.htm

Just something to think about.

Al

**Acidtech** · 07-05-2010

If you are using DC motors and encoder wheels either get encoder wheels with a home position builtin or you will need a home sensor(physical/optical switch) for the home position. I'd suggest the magnetic sensors from US Digtial instead. You can get absoulte encoders so on power up you will know exactly where your arm is.