4-26-12:
This project hit several roadblocks. I'm still not sure how to address some of them.
The foremost problem is the power supply. Initially I thought an SLA battery would be sufficient. They're just too heavy and I believe the internal resistance would have problems feeding the system. I found some 18000mAH (or just 18AH) Li-ion batteries but they also are only good for ~3A output. I'm considering some lipos but for a 3S battery with enough capacity to let the bot run for more than an hour it will cost a pretty penny. I thinking of downgrading my 4 amp TEC unit to a smaller 3 amp unit with it running off a separate lipo from the rest of the bot. Still looking for alternatives.
The second problem is the AVRcam. Although I've got it made there seems to be a problem with the ATtiny feeding the clock signal over I2C to the Mega8 correctly. I've recently gathered all the parts for a simple two-channel oscilloscope. Once I make that I think I'll have a better idea of what the problem is.
Other problems include the drive system (I've never dealt with a big, heavy bot like this before). How much torque will be needed? Wheels or tracks? Direct drive or belt/chain drive? I'm trying to avoid expensive motors but I'd hate to buy some cheaper ones and watch them stall right out of the gate.
I'm trying to avoid spending several hundred dollars on this project. I'm not sure there's any way around it though.
11-23-10:
I've always wanted a refrigerator full of beer to follow me around at a party. At last a modified version of that dream has got momentum. I've got the chinese to thank for it too. The plan won't be using a refrigerator but a 12 liter thermocooler I got from eBay.
The plan is to have the (~4 amp) thermocooler running off a 12V 12ah gel cell, mobilized by a PICAXE and some whopper 9A stall current, 50kg-cm gear motors driving tracks (if I can pull it off). I would also like it to have a 5W solar panel that it can raise and lower to provide shade and some extra current during the hot, sunny days. I hope to use something like AVM or the CMUcam to give it object recognition so it can follow me around at a party or bbq.
I just got the thermocooler and it works great! The door has problems latching correctly and even when it does there's a small gap around the door seal. I tested it out and immediately took it apart and took pictures.
Front and inside. Soda can for scale:
Back side, with and without panel:
You can see the hot side of the tec cooler, the centrifugal fan to cool it, and the little PCB. The PCB had a big DPDT center-off switch to reverse the polarities to make the unit heat instead of cool. There's a couple resistors and diodes. That's about it:
Cooling unit without hot-side sink:
Notice the terrible seal to the cold-side of the operations:
Pic of the how the cold-side sink sits in the chamber:
Notice the included thermal switch. Unfortunately it's only to keep the thing from melting down when it's used to heat things. With the cooler selected it just runs forever...
The inside sink comes with its own fan as well:
Pro's:
- Works really well at around 70deg F.
- Came with its own 110VAC-12V 5A power supply and a cigarette lighter attachment for car/truck use.
- Came filled with insulation already.
- Overall well made.
- Red!
Con's (Must fix's):
- Redo the seal with weatherstripping.
- Must investigate latch. Maybe switch to magnetic.
- Stuff scrap styrofoam in the gaps that curse the tec unit's insulation.
- Replace hot-side fan with 120mm fan, attached CPU-cooling-fan style.
- Incorperate pre-purchased 12v @ 5.4A power supply for future power demands.
- Redirect drainage from condenser tray to harmless location.
UPDATE: DEC. 8, 2010
I decided to try and clone an AVRcam to use for the tracking system. It's no longer state-of-the-art and I had problems sourcing some of the parts. Most noteably was the OV6620 CMOS camera module. The problem is it's been replaced by the 3.3V OV6630 module. Although it looks to be a relatively easy adaptation, I'm a cheap ass when it comes to my robotics. The 6630 goes for ~$40. I found an old webcam that uses the 6620 module. You can find it used or even new (I did) for ~$20.
I'd hoped that I'd be able to hack into it easily but it was not to be. I ended up having to remove the camera chip itself off of the board to plug into a custom PCB made on EagleCAD. Here's some pics:
The insides from the underbelly:
The lens seems to have an IR filter and has a manual focus:
Camera without lens and some SMD bits:
Ahh... some desoldering, some deft razor work, and the PCB yields its gold:
You can see some of the pads are still attached to the chip:
Now I have to bag an ATmega8, Tiny12, some bits, some pieces, and a few other things before I proceed. Got the hardest part out of the way, though :whew:
) and tank treads? Treads sould be better since the better climbing cables, slippers and other things laying around the floor.