Skip to main content


Showing posts from November, 2009

Best laid plans...

Well it seems that every attempt I make to reduce cost on this robot just comes back to bite me in the end. I think I've learned my new shit and don't try to cut corners. I'm referring to the motors and the motor controller... While investigations into the motor controller resulted in a good design (based on that of the Open Source Motor Controller ) the cost and time needed is prohibitive at least for the motors I'm going to use. So I've ended up purchasing two 9A motor controllers (one for each drive motor). They work very well for these motors (they are way bigger than necessary). One issue came up when I mounted these to the chassis though... Two of the controller's mounting holes are attached to OUT A on the PCB as you can see in the picture. So when I bolted the things to the bot and started using them, a full 15V was applied to the chassis. This burnt out two cheap sensors (fortunately I had enough replacements on hand) and it wouldn't l

Motor Control Circuit

Update: This circuit doesn't work (thanks Sparkfun Forums folks) revised version will be in next post. So I've worked out the motor controller circuit I'll be using. I've ordered the components too. Hopefully when I get them it will work as planned without too much modification. Or the Google Doc The major components: Power MOSFET NPN Switching Transistors Opto-isolator/Photocoupler It's less complicated than the circuit makes it look... It's really 4 identical circuits (which I show in lower part of schematic) attached to the MOSFETs of an H bridge. The optoisolators ( PS2501 ) are also a single package so wiring won't be as complicated either. Please feel free to comment or suggest changes... I've never built a circuit for high voltage/current motors like this before and could really use another set of eyes on this. (Especially if it looks correct, I need positive reinforcement as much as criticism :)

Change of Plans...

I've visited about 15 local hardware/hobby/auto parts/tool stores in the last 3-4 day looking for ideas and ways to turn these drill motors into drive motors for the robot. I've also logged about 8 hours of research into gears, gear types, gear ratios, and speed/torque conversions. I've decided to scrap the idea of using these motors as drive motors. The two main reasons are cost and unknowns. It costs as much to buy geared motors as it does to buy the gears to get these working. These motors are terrible as far as documentation goes. There's no way to find out their intended voltages, current draw, stall current stall torque and on and on... Because of this I don't know how far they need to be geared down. It would take some trial and error at my cost. I don't have the time or funds to do it. The other reason is complexity...It would take a fair amount of machining to create mounts for all the hardware in a custom gearing solution. Don't believe me? Have a

2 Days in and already Over Budget

I did some scouting at local pawn shops for suitable power tools w/ strong motors over the last two days. I ended up finding 2 14.4V Craftsman drills (each of which came with 2 batteries and a charger) and a 14.4 V Black and Decker circular saw (w/ 1 battery). Grand Total $140...Doh! I shopped around with the intention of matching the two drill motors so that they would be balanced in torque/current/dimensions/etc. I made the assumption that being the same voltage and brand would be enough to get evenly matched motors. Unfortunately when I disassembled them later I found that the Larger (red) one had a motor much larger than the other (gray), and the transmission was very different... The circular saw has a motor similar to the larger drill. All three have different drive gears. So the plan at this point is to ditch the transmission from the larger motor and the gear box of the circular saw and find gearing for these two to make them drive motors. Next time I think I'll just bu

2 Upcoming Competitions

Okay so the main reason for this new website/blog (for the time being) is to chronicle the build of a super sumo style robot for Sparkfun's RoboJoust competition on December 6, 2009. As I'm currently at my childhood home in nowhere's-ville Kansas I'm near enough to the competition site (Boulder, CO) to actually participate. I'm looking forward to touring Sparkfun's building and meet other robotics folks. Info on the competition is here . The basic idea is to have two robots start at opposite ends of the track (below) , meet in the middle, undergo epic battle conditions and finally limp to the opponents starting point. First prize for the event is $100 so I'm considering that to be my budget for materials. With that budget in mind I'll be trying to locate old cordless drill motors (for locomotion and weaponization). For now I'm still sketching and brain storming, but due to the budget I'm going to be keeping things very simple: heavy - (battery/