Let's Make Robots!

MiniTrack

Navigate around via IR, drive upside down

I had an idea to build a tracked rover, capable of driving even upside down. I came up with a design for each side to have a drive gear and two idlers in a triangle formation. And with that I started ordering the parts I would be needing, which unexpectedly arrived on a saturday. Sweet!

After drawing it out in pencil and getting rough dimensions I started cutting pieces out of 1/8" HDPE.

Pictured are the 150:1 micro gear motors, DRV8833 motor driver, Fio V3 with Xbee, and the tracks and idler gears.

Originally intended to use a flat 4.8v 2/3 A NiMH pack, but I managed to make the body a bit too small. I've got a smaller, cube shaped pack ordered, hopefully it will fit a bit better. I also had planned to use a Fio V3 with an Xbee, but I'm also finding that to be too tight a fit. So I'll likely resort to finally using the Arduino Pro Mini I picked up a year ago. I would really like to have that easy wireless connection, but it may not be in the cards. I'll have to see how an xbee carrier board would fit with the pro mini and motor driver...

Also, need to trim some screws down to size...

Motors wired, with filtering capacitors. I'm tempted to make a wider base and make fitting everything that much easier. This is how it sits right now.

Still to do mechanically:

  • Decide on how to mount an IR sensor to the front for object detection.
  • Nail down the microcontroller I'm going to use.
  • Mount a power switch to one of the sides.
  • Googly eyes?

 

2/11/2014

Mounted microcontroller (Pro Micro 5V) and the motor driver. Slightly concerned about the proximity to the metal brackets, but everything clears as it is. And should be space for the battery once it arrives. Just. Also posted video of first (successful) motor test!

 

2/13/2014

Mounted IR sensors to front of the bot using the ever useful hot glue. At present only the left sensor is connected. As such when it detects an object the bot picks a random number between 1 and 50, if it's below or equal to 25 it turns left, and above 25 it turns right. He's simpled minded at the moment.

I haven't quite met my design goals yet, the front end sticks out a bit too much allow driving on the front of the bot. Raising the mount points for the lid may alleviate that, allowing the lid to fold further in.

Power switch mounted to the underside rather than the side. More than enough ground clearance for the type of surface I would run it on. And precious little room on the sides to mount the switch anyhow.

And just because this is the first bot I've built from scratch, I felt it worthy of a little badge of honor. Had to eventually find a place to use one of those stickers!

2/14/2014

Added one more fun video of the bot tumbling down some stepped boxes.

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Wow. I need to be better about checking LMR robot build logs, this guy is amazing. I'm a bit if a sucker for anything with tracks/treads, but the triangle flip-over design possesses utility and robustness. I don't suppose I could beg you for a detailed BOM? Full disclosure, if the mechanics are cheap enough I'd shamelessly copy you, sir. And like a broken record: May I suggest a pair of HM-10s? 300 ft LoS for around $11 each.

Here is everything that went into this little guy:

12"x12"x1/8" thick sheet of HDPE (or material of your choice)

  • -More then half of this is still left over, so more bots to be made!
  • $4.23 Purchased from McMaster Carr

2x 150:1 Polulu Micro Metal Gearmotor MP

Pololu 30T track set

Pololu Idler Wheel/Sprocket Pair

Pololu Gearmotor Bracket Pair

DRV8833 Dual Motor Driver Carrier

0.1uF Ceramic Capacitors (You can probably get away without them, but you really should)

Rocker Switch SPDT 10amp

3" Female to Female Jumper wires

x2 0.100" Breakaway Male Headers 1x40pin

x2 Sharp GP2Y0D805Z0F IR sensor 5cm range

Sparkfun Pro Micro 5V 16MHz

Hobbico Hydrimax NiMH 4cell 4.8V 1600mAH 2/3A Square battery pack (that's a mouthful)

8x L-brackets from the local hardware store

  • ~$2-3

x14 short screws (mine were 6/32 and 1/4" long) and matching nuts

  • ~$4-5

Small hinge with hardware

  • ~$4-5
  • Mine came with tapping screws, they were too long for the material and would stick out, so I found some small bolts and nuts to replace them in my stash.

LMR sticker

  • $priceless

 

My calculator says $136.56 total, I was thinking it was more.

I would love to get any kind of wireless connection into this little guy, but as it is there is just no room inside. I would definitely plan ahead better next time.

Neat concept! Somewhere between Rhex and a Segue. I like the idea of it working no matter how it gets flipped (unless it lands on its side, I guess.) I'm wondering if the faces parallel to the planes defined by the tracks provide enough clearance to make the tracks useful on terrain uneven enough to upset the platform. Have you tried it off the table yet?

So far I haven't tested it on anything more then what's in the video. There is certainly less clearance on the top halves than on the bottom. If it did find itself upside down on uneven terrain it would likely just get hung up. But it was a fun idea I wanted to try, and so far I'm happy with it.

Still a fantastic and innovative idea.

Thanks. Maybe once I'm happy with this bot I'll go larger scale and work out the kinks.

Tonight would have been spent testing the IR sensor, but instead I had my first adventure with burning a bootloader back onto my pro micro. Not sure if shenanigans playing with hardware interrupts, or possibly drawing too much power through the usb port caused the flake out. But lessons learned, disconnect the power to the motor driver before programming the uc. And have a wired  up reset switch handy just in case. :)

Arduino as ISP FTW. Board is back to accepting code and running the bot again, so back to work.

Not sure what range you require, but a bluetooth on the FTDI will give you a serial interface to communicate in a very small package.  The XBee and it's associated carrier are very nice, but twice the size of the Bluetooth.

 

 

This chassis is really cool.  The access panel design is very clever.  How does the panel stay shut?  are the brackets threaded or something?

The screws are threaded into the HDPE, and when screwed down they catch the brackets and keep the panel closed. And it all happened by coincidence. :)