I PUT MOTORS ON THE BIG TANK! (Patreon)

Hi everyone! 

First of all I wanted to apologise, I had a rough past month (Stomach virus, cut badly my finger and got the flu end to end) and couldn't make more videos, this one didn't take a month. 

But hey! The big tank has motors! Those may seem familiar because are the same that went on the minitank and the previous big tank.

I'll give you a bit of info so you can follow my thought process when designing this tank and where are the improvements:

The treads: The nylon (fish tape) pins are waaay stronger than the previous nylon filament pins used, those will never ever break. And in contrast with the steel ones used on the minitank, those wont rust. I also swapped the end caps for small screws so they don't get loose and let the pins escape, it seems that the side forces of the pins under friction are quite large. This, as you can see in the video makes for a very quick maintenance disassembly, which is another plus. 

The sprockets: These are direct scale ups of the ones on the minitank, one of the purposes of the minitank was to test what was going to be on this big tank, and that sprocket design proved to be perfect. There's no way that the treads are going to skip even if there's no tread tensioning mechanism, I may even remove an extra link on the treads so they are tighter as the nylon pins add some springiness to it that may allow it.

Axles, shafts and rods: Everything in the drive system is through hole, that way there's no option for anything slipping. In the first part of the video, I did every hole with a 4.5 drill bit and all the hardware was M4 which added an unwanted play (the shaft would rotate a few degrees before transferring the power) that bent the bolts until they broke. In the second part made all the holes 5mm and all the hardware M5 and now there's no play and everything is a bit beefier. The only shaft that hasn't been drilled through is the motor shaft because I'm waiting to see where the encoder lands to see were I need to put the holes for the output sprocket, but I'll drill it for sure. 

Belts to Chains: Adequately tensioning and aligning belts proved to be quite difficult and ended up with a few destroyed belts and disappointing tests. The chains I used require no tensioning (68mm between centres and that's it) and I doubt that they'll break under this kind of load. 

The electronics and motor: The combination of motor and controller is crucial for this tank to be drivable. I choose these motors because they are low KV which means that they can turn slow with a lot of torque, but they are sensorless which means that no controller can make them turn slow because the controller does not now the position of the windings relative to the magnets unless the motor is turning at speed. So I had to choose between swapping motors or swapping electronics. I really like these motors so I opted for the later and got an Odrive which is a very nice controller and an encoder on the motor shaft that will allow the Odrive to know where the motor is at low speeds. This combination should give us an insane amount of torque and control at low speeds, which is ideal for a tank, and an insane top speed that would probably disintegrate the entire tank. 

And that's it, that's how we got here. The Odrive allow control through an Arduino, for example, so I'm considering my control options. My first option is to add pedals in the front so each foot controls one tread back and forth but I'm still debating on the associated safety issues. 

Thanks for your support and as always, comments suggestions and "that thing that I didn't thought of" are welcome in the comments.

Enjoy!