Let's Make Robots!

XMOS Challenge : ONR robot beginnings

Description of the ONR (maybe a real name TBA)

This robot is to navigate outdoors from point to point, possibly going through a series of predetermined points. Point location can be marked by traffic cones, GPS coordinates, or other orienteering markers as detailed in various contests like Robomagellan or the DPRG outdoor contests.  Requirements include finding and recognizing the point, as well as negotiating any obstacles between points, and maintaining a remote stop.

Possible additional abilities can include a simple on board user interface for point entry, video and audio feedback, object manipulation, complete remote control, and solar charging.

Basic bot parts so far :

Possibly various sensors, probably sonar with analog or pulse width output. Maxbotix LV-MaxSonar EZ1 likely. Might try Sharp IR sensors though expect washout in sun.

Parts to do :

  • Determine 2 or 4 wheel drive, tricycle or 4 wheeler 
  • Get a good coupling of wheels to the motors, unsure of current hack
  • coupling of encoders to protect them, but maintain good count. 
  • consider remote control options, to take over or remote stop in case of error - Vex radio or XBee?
  • check detection of likely obstacles - sonar or IR detection of plants, wire fences, streams
  • consider likely sensor placement to maximise detection of obstacles 
  • consider video/audio feedback, range

That's all for now.

 

 

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I like the look of those motors and wheels. It looks like the wheels might have a set screw on the hub if you look closely, which would simplify connecting them.

You should post the description of your robot and what it`s supposed to do. I can`t remember what your idea was and can`t be bothered searching the xmos competition thread for details :p

Description done!

Sadly the wheels have bearings, much like other scooter or skate wheels. I'm hoping to use those bearings on whatever shaft I mount the wheels on, and attach the wheels to the motors somehow. They have a circular slot outside the bearing just a bit, that I've tried to use. I have a sort of fabbed plastic cup, with a sort of crown end that engages the wheel, buit not very well. Maybe it will be adequate. The motors have an off size shaft, with an hexagonal hole in the end. I've got a hex key embedded, but not real confident in the mechanical connection.

Hi, robologist!

Just a short question; why dont you build your own motor driver instead of paying 60$ for a simple driver? Something like this should work great with your motors(which look awesome, btw). Would reduce the cost with ~40$ 

 The L298 based device linked would be burned fairly quickly by these motors, as I think they idle around 3 A, and peak near 20 or so. Most automotive motors will have higher current draws, so the smaller h-bridges won't quite make it.

The Pololu device is a good value, difficult to get something with similar current capability and all packaged up on a nice PCB for the price. 

Besides, I already have the Pololu h-bridge.

 

Gah, I misread the motor specs on the Parallax webage. Thought it said 1.5 stall current ... Reading the specs on the Skycraft Parts & Surplus webpage shows that Parallax has a different opinion on what the no-load current for the motors are on 12v. Parallax states ~150 RPM @ 12.0 VDC, 1.50 A, no load while Skycraft Parts & Surplus says 12 Volts: 163 RPM, 3.3 Amps (No Load). 

Anyhow, I see your point regarding the driver, the 298 is a bitch to use anyhow due to the stupid pinlayout :) Guess, I'm just a bit suspicious always trying to find a way I can make the stuff myself, but in this case it looks like you'll need it. Good luck on the bot, btw.

I'd found a video that Ken Gracey of Parallax had made, showing 2 motors running at around 3 A with 12 volts pushing, so they apparently are 1.5 A each with no load. They do pull a lot more in stall, which is the parameter to select your h-bridges for. Parallax uses their HB-25 to control these, which uses a VNH3SP30. 

 It's good to make things yourself, but sometimes you can get something better made for cheaper. I couldn't duplicate the Pololu h-bridge in a small quantity for the price they have it at.