I've started calling this robot by this name because I discovered that a white plastic 5 gallon bucket fits nicely over the traction unit. My kids call it B2D3 (thinking it is similar to R2D2 of StarWars fame).
Drive wheels and motors notes (I note that National Power Chair sells rebuilt wheelchair drives at a variety of prices from $136 to $200+, depending on the gearing and torque) (and so does C&H sales, for the same price). The wheel chair motors are vastly over powered for this application.
Traction Motor Control notes For now, the pair of Novak ESC's in combination with a V-Tail mixer module (about $30) works to drive the bucket around. The V-Tail mixer allows one stick on the R/C transmitter to drive the two controllers in a sensible fashion (i.e. push stick straight forward to go forward, etc.). Eventually, I can either stick the Vantec controllers in, or I can stick with the Novak units and drive them from the SSC and a serial port.
Stacking a second bucket on top of it makes for a nice package, especially if the top bucket is on a bearing and can turn independently of the base. Some preliminary work has been done on using the top bucket as a form to hold a suitable omnidirectional antenna (although, see below about the bucket whip). A 6" lazy susan bearing mounts nicely on the base (i.e. the uppermost surface) of the lower bucket. The 4" hole in the middle of the bearing gives plenty of room to feed wires, etc. up through from the base. The lid for the second bucket is bolted to the bearing, providing a handy mounting flange for the upper bucket. A "quarter scale" R/C servo (Cirrus CS-400BB, since discontinued) scavenged from the snake robot serves to move the upper bucket relative to the lower one, although, the 90 degree motion range isn't as much as I'd like. This is more a problem with my R/C transmitter than with the servo, which actually can swing 180 degrees.
Bump detectors. Standard NO push buttons mounted around the base, and then covered by a "bumper" should serve nicely. The buttons can be "scanned" by a 74LS138 or something from the Rabbit.
Power is provided by some "gel-cells" (probably actually starved electrolyte or sealed lead acid). Here is a description of power supply and control issues.
The bucket bot has a video link using a small camera mounted on a servo and an amateur radio transmitter in the 70 cm (420-450MHz) band. The servo provides 90 degrees of elevation motion. The R/C transmitter is set up with one stick controlling Az and El for the camera and the other stick controlling the locomotion.
I started with an old color camera I had which has very nice resolution and dynamic range, but it didn't have any color signal when I tested it (B/W only) and it gets pretty hot, so it's drawing a LOT of DC power. Therefore I switched to a low power monochrome camera from All Electronics (Cat # VC-360, $49) F2.0, 3.7mm lens 1/3" CCD (nominal 90 degree FOV). At first glance, it looks like monochrome may not be a very good way to go, and I may want to go get a color camera. It's hard to navigate by using the camera in monochrome (too many visual cues come from color)..
I've used the PC Electronics 70cm band transmitter (more at the ATV page) feeding a quarter wave whip/groundplane which is built on the upper bucket. The ground plane is 4 strips of 1" copper foil tape (13 cm from center to edge) and the whip is a piece of bare #12 AWG wire (18 cm tall from bucket surface to tip). It seems to work ok sitting on the bench, and preliminary NEC models show that the pattern is fairly omnidirectional, with 7.2 dBi gain. There are some pretty big nulls around 13-14 and 42 degrees above the horizontal, because it is a vertical that is 1 wavelength off the ground. The match is pretty uniform at 2:1 VSWR, which is not too hot, because the characteristic impedance is around 26-27 ohms. Figuring out a way to "droop" the radials or using a sleeve dipole might be a better approach. (Sleeve dipole impedance will be around 70 ohms), or, implementing the bucket Lindenblad, which would help kill the really big nulls from ground reflections.
The receiving end of the link is a PC Electronics TVC-2G which downconverts the 426.25 to Channel 3. I have a small LCD TV velcro'ed on to the TVC-2G enclosure, or I can feed a bigger TV. Oddly, the RCA (Radio Shack) LCD TV will tune to the 426.25 on the UHF band. This is odd because since UHF TV starts around 470 MHz; perhaps it's an image.
For now, on the bench, I do the legally required ID by holding up a sign with my call letters on it in front of the camera. On the robot, I'll put a sign in the field of view when the camera is tilted full up or down. This is a heck of a lot easier than adding a titler or keying the video on and off or adding an audio subcarrier (although, the subcarrier might be kind of nifty... I could put a mike on the robot).
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Top of turntable bearing mounted lid, showing 430MHz ATV transmitter,
servo for elevation axis, and small CCD camera. |
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Details of azimuth drive. Top side, showing "lollipop" of lid
used to connect to control horn on top of quarter scale servo. Bottom
side, showing bracket mounting servo to "bottom" of lower bucket. |
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robot/bucketbot.htm - 26 January 2002 - back to robots - back to Jim's home page - Copyright 2001 Jim Lux (mail)