Motor shaft stress



At the MIT makerfaire i did not have a maximum mass-limit, and unfortunatley this resulted in the motor shaft bending significantly (shown right). Time to add a rider max-mass limit :/

Wheel leak

A slow leak developed through the aluminum rim in a location i had welded over. After a number of attempts (and a number of trips to re-seat the tire) I took some advice from a comrade "dont they make friggin inner-tubes for those". Turns out they do and they are fairly cheap! [link]

Tire desintigration

It turns out, you can only remove and re-seat a tire a heavily used tire a fixed number of times before it falls apart.

A tube from ebay fit the bill just fine, I seated another used tire, from the kind folks at F1 Boston, removed the valvestem I had added and carefully inflated the tire, using soapy water to help get the outer rubber tire to seat well on the rim.

GEARS

The gears themselves got fairly gnashed-up. These are 36 tooth module-1 gears with a 20 degree pressure angle, stock, they are made of nylon. Mostly visible is the aftermath, a few missing teeth and a few smushed ones as well.

Unfortunatley gear mushing this is a common failure mode observed by the folks on endless-sphere [link]. I quickly modeled a MODULE-1 36 Tooth gear for waterjeting out of 1/2" thick steel. The part came out great, but it appears the waterjet offset was a bit off (the teeth are artificially skinny). The part would work, but be rather noisy, as the added back-and-forth backlash would be fairly high. Fortunatley there are Rob Reeves in the world who know how to make legitimate gears. MORE GEARS AHOY

Out come the soviet-era gear cutters! I water-jet some round steel stock to be used as blanks for the 'reeving' process, Rob fabricated a spindle with a dye-cut thread for keeping everything in place.These stacked rounds will be lathed to the same size and used in the spur gear-making pricess. The outer diameter of the rounds, as well as the inner dimension are very specific, too large and the planetary geartrain will not fit together, too loose and the inner flanged bearings will not press-fit inside, and the gears will have a boatload of backlash.

A large portion of the gear-cutting process is prep-work. Shown (right) is Rob cutting down the samples and building a spindle for holstering the pre-cut steel and brass rounds. The holster consists of a shaft, adapter to mount to an indexing head and dye-cut threading for tightening the steel & brass rounds in place.

Setting up the gear-cutting head



The gearcutter position is critical, needing to start precisely in the center of the round. The cutting depth is also fairly critical as the depth offsets the start of the involute curve, causing the mating surfaces to not mesh properly.

Switching a 36V hub-motor from nylon gears to steel

Previously (above) I had used the 48V variant of the 8-fun motor, namely because the first servo controller i had access to was only able to run at 6A but allowed for high voltage operation. With the newer A-M-C drive, i could now operate at a more tolerable battery voltage

Steel gear lineup

Shown (right) is one of the steel gears Rob synthesized. Its a frigging fantastic fit. Further right is a re-welded, wirewheeled planetary holster with the three steel gears in place as a mockup. IT LOOKS FANTASTIC.

Setting up for cutting out the space for a flange. The gear is held in a rotary table by clamping onto the flat face of the hobbed gear and a precise measuring head is used to locate the center of the gear.

Milling the flange holster

The bearings chosen for these gears are [link] 22mm x 8mm x 7mm flanged. The flange constrains the gear from coming off inside the planetary and a press-fit prevents it from colliding with the base plate of the planetary holster. Shown here Rob uses a rotary table and a small offset to mill out a press-fit socket for the bearing to sit in.