I'm really excited because I just finished building the chassis for my new 6WD robot.
<right click open in new tab to see full size, sorry still getting used to the forum>
Yes, there will be structural members installed to eliminate the flex in the frame. Waiting on dimensions for batteries, motors, etc.
Each side of the robot consists of three wheels directly connected via roller chain. I bought the chain, sprockets, shafting from mcmaster-carr, the bearings from some knock-off site. Acrylic I bought at $1/sheet at TAP plastics locally. Screws, shims, washers, etc from Lowe's. The tires and wheel hubs are from robot marketplace. I have a cheap Indian-made 5A motor controller, but I'm willing to bet I'll blow that thing to pieces the first time I try it.
I built these axle assemblies and screwed them into the main platform.
I have a running blog which I will continue to update here: http://darknrgy.typepad.com/darknrgys-blog/6wd-robot/
. I have a ton of information about the robot, the design, my trials and tribulations.
This is my second major robot project. My overall goal is to build a solid telepresence robot that will withstand any kind of environment. One day I might even use 3/4G and roam around the city
. Imagine that.
My first robot was a real piece of crap. It worked, but it was so underpowered, everything broke constantly. It was an amusing project though, and this video summarizes it. Please excuse my dorkiness.
I have a ton of ideas to improve the remote control of the new robot. I plan to use motor encoders to control motor speed for a more reliable tracking. I have some ideas on interface to get around the lag you get across the internet. I also plan to incorporate distance sensors and add some autonomy; automatic collision avoidance, etc. At this point though, I just have a platform, and I'm ready to do whatever.
I should probably use arduino, but I am just addicted to the raw connection to the atmel chips and building my own prototype boards. Plus, considering how much crap I want to put on this robot, I'm going to need multiple processors - motor control, sensors, management, etc. Yes, I'm cheating a bit by putting a laptop on the robot, but it's for a good cause. Streaming video, gps, wireless network, 3G, anything is possible. I'm planning on getting a netbook anyway so it works out.
SO, I do actually have a question. I'm trying to find the right gear-motor, which I'll be connecting through some more roller chain, preferably at 1:1. I'd like to have about 2ft/s and I'd like to be able to propel up to about 10 pounds ... straight up. Each motor will then need to lift 5 pounds. I calculate this to be 22 Newtons. My wheels are 4.25" so I calculate about 1.2 Newton-Meters of torque. Converted to oz-inches this is 170 oz-in
. At 2 feet/second and 4.25" diameter wheels, I've calculated I need about 108 RPM
First off, I would greatly appreciate if someone double checked my work. I already had my dad check it, but I'd like to get some more eyes on the problem. With these calculations, I've determined that this is the perfect motor: http://www.pololu.com/catalog/product/1445
. It's overpowered in every respect (200oz-in, 150RPM), it fits within my 12-24V requirements, easy to mount, 5A stall to fit within my motor controller specs, and has an encoder for measuring speed. Sweet!
Are there any rules of thumbs on power to weight? I picked 10 pounds of force for a ten pound robot because I want it to at least be able to go up a 45 degree incline with plenty of power to spare. There are some drive train losses because of the chains, but it seems to be pretty negligible.
Otherwise, any feedback on the design? I'm a programmer by trade and I do this for fun, so I half expect to be digging myself into a hole.
Anyone have any experience using ATMega8 for motor encoder data? Looks like even if I look at only one phase I'll be dealing with around 40kHz of interrupts. I found some ICs designed for decoding, but are there favorites?