Body Building And Torque Concerns

It's been a long week at Wicked Web Creations. I'll be happy to have less projects on my workbench as more and more of my projects progress toward completion.

After spending most of the month in the shop, wiring up my classic truck; I've been making steady progress on the Johnny 5 Project.

There have been some trials and trebulations along the way, to be sure, but I have high hopes for the future of this project.

A main concern of the robot will be getting enough torque to adequetely propel the bot while using minimal cost. If this was a better time for me financially, I would be able to provide a more reliable solution than the plans that are currently underway. That being said, I have proposed a feasible solution for my power needs.

The main problem with this project is to provide a workable solution for power while keeping costs and weight low.

POWER:
At first I thought about using a lawnmower battery or two to provide 12-24DC current that would use an ample motor shield(such as the Sabertooth) and then buy two big DC motors to spin the treads. While great in theory, my pocket book was a tad light to be able to accomplish this task.

So enters, theory 2. Use an adafruit shield with RC motors. Which is a good idea because I already had motors sitting around which saved me a pretty penny and the adafruit shield was only 15 dollars, so I could use it for other proto's even if it didn't have enough torque.

The adafruit shield is rated at 700mah stall current per channel and utilizes a 4 channel system for AWD control. So, surfing around polulo (sp?) revealed that I could indeed get some sumo motors for it that use the external gearbox. So, I could, in theory, get 4 medium power motors to work on the card without adding a heatsink and using the card under light duty.

These motors are cool if you can afford them and I may upgrade the bot to feature these in the future.

One problem I did run into was getting the right motors. After discovering that my little mshield would in no way make my salvaged printer motors move bike chain, was dissapointing, as it would have been a great way to reuse parts. So I junked the jb-welded motors with the roller blade wheels, ball bearings and all that other good stuff for a set of Dumas Rc 6V motors in the rear, and two Hacker Sprint 6V in the front. I'm using an 11.4 (?) V Lipo for the power supply, so I don't even notice a voltage drop when the system is running at full boar. Usually, the drop would be about 1V~1.2V per channel with this setup. I could have just as easily used a 7.2V RC or a pack of AA in a 9V config, but I like the idea of having the option to pump out more juice, just in case.

TORQUE:
The Dumas motors are running at 8mhz while the two hackers operate at the higher 16mhz signal to allow the back wheels to produce more low-end torque, while the front stays light and fast. 

The chassis of the robot is basically a tank config with a bot sitting on top to provide interaction. The bot sits about mid-ship, just above the rcbatt and the mshield, while the systems battery lights the rear, and the camera/touchscreen pilots from the front of the robot.

The systems battery is the heaviest component, next to the exoskeleton, and both components are mounted so they are weighted toward the rear. This is why, the back wheels need more torque. However, at this time, it is impossible to tell exactly how much torque I willl actually need to get the robot moving, as I have no access to a digital scale of any kind.

I'm betting at around a 80:1 geared system, would do a reasonable job, but for now the big dumas's will have to work.

****Fun Fact**** Dumas motors are ususally used in hobby boats, the big, reproduction ones and not the speed boat kind. Hacker Motors, or more specifically, the Hacker Sprint's that I'm using are typically used for airplane props, the Park Flyer model is the most popular that uses this particular model.