I am back. My older work was posted under Prettybird, but that account stopped working. This one of my newer designs. It uses a back steering wheel instead of a coaster and can work well on smooth or rough surfaces. It is also designed to carry some weight. I have loaded it up to 1.5 kilos so far (about 3 lbs). So far I have used the Parallax Basic Stamp (BS2PE) and reciently added a Parallax Propeller board. I am finally in the process of learning the prop. I like the back wheel steering because it dosen't get stuck on sidewalk cracks and such. It uses 2 x 3" model airplane tube tires and has alot of traction and room for expansion.. Work still in progress.
Roam for now
- Actuators / output devices: 2 servos modified for continuous rotation, 1 servo for steering
- Control method: IR and X BEE in the future
- CPU: Propeller in the future, BS2PE stamp for now
- Operating system: windows XP
- Power source: 7.2V (motors) 9V (electronics)
- Programming language: pbasic, Propeller Spin
- Sensors / input devices: IR, Ping ultrasonic
- Target environment: Indoor and outdoor smooth or rough surfaces
This is a companion discussion topic for the original entry at https://community.robotshop.com/robots/show/3-servo-robotic-platform
Hey, another robot with both
Hey, another robot with both differential drive and a steered wheel. How have you dealt with getting the angle of the steered wheel to match the relative speeds of the two drive wheels while turning?
I have a blog about this type of steering, Why Tri? A stupid way to steer. Don’t take offence from the title; I have learned a lot trying this way to steer. I’m curious what you have learned.
Trial and error
Thanks for your intrest. I found with 1 wheel turns (one wheel not turning) I guessed about 45 degrees for the back wheel and 2 wheel turns about 90 degrees for the back wheel. As you can see by the video, a little more tweeking for the movement wheels can be done or mabe when I get better encoders would correct the drift. That is a simple servo test program I use on my new robots. As I mentioned, this one can carry some weight on most kinds of surfaces from shag carpet to cracked up sidewalks. Work still in progress until I learn the prop more.
It looks like you did a
It looks like you did a pretty good job just by trial and error. You are correct that for a two wheel turn (drive wheels in opposite directions and same speed) your steered wheel should be at 90 degrees.
For Why Tri, I purposely placed the center point of the three wheels in an equilateral triangle to make the math easier. So for your one wheel turn, you’ll need to determine the angle specific to your platform. For an equilateral triangle, this is 60 degrees.
