So, TOBL. It'll be a 6WD robot driven by either two or four wheels at a time. This means it's pretty inefficient. However, the goal is to make this little guy freaking unstoppable! The triangular six-wheel configuration therefore is to allow it to roll over and then carry on its way (see MS Paint diagram below). For torque, I've bought a pair of Hitec HS-82MG servos, as promised. I explored the option of upgrading the gearset in the one working HS-81 and buying a new HS-81MG, but for $5 more ($45 total with shipping) I got two brand new servos with upgraded motors, controllers, metal gears, and ball bearings. Anyways, they put out 28kg/cm (whatever that means) each at 4.8V.
The drivetrain will consist of a splined pinion gear coming straight off of each drive servo to spur gears on each of the three wheels. From what I could find online it made most sense to use 48 pitch gears, which means I will have to be extremely careful when machining the plates that align the them. In the interest of cutting a little weight and getting practice with small-scale precision machining, I've made these plates as ridiculously intricate as possible. I should have a plate of 1/8" 6061 aluminum tomorrow so look for a fabrication post sometime soon. I'll do my best to stick to these designs no matter how much I'll regret it while on the mill.
There will be two of these "drive units," with the servo-sides facing each other and the electronics and battery sandwiched in between. Speaking of the electronics I've decided to go all out and print a board for this little robot. It'll basically be an Arduino Nano 3.0 shield, so I think it's definitely worth while to design an accomodating platform that could be of use in further projects, and allow the expansion of this one. Perhaps once I get TOBL to move I'll start adding some sensors to the leftover pins. For now, It features a socket for an Xbee and an off-board linear 5V regulator. This may seem excessive since the Nano has an onboard regulator built-in. However, I'm a bit of a servo nut and traced four of the PWM pins to 3-pin headers specifically for servos. While I'm only using two micro servos in this project, I can imagine using more on future iterations and Nanos are not cheap to replace.
Click the schematic for bigger version.
First Schematic! The boards may not be printed for a while, kinda hoping Santa's elves will pick up the tab on this one because this project is getting quite pricey. I've already put some work into this so it shouldn't change much. I'll post a shot of the board layout and more details once I finalize and send that out. With the dimensions of the board I'll have a better idea of what the chassis will look like. I will be working hard and machining as quickly (and carefully) as possible over the next couple weeks before Thanksgiving Break!