Dyne's LD-F1 (D-O concept) build

[Dyne]

Here's the footage of the mechanism.  it's pretty clearly the belt that's slipping.  You can see the gears and motor are turning just fine, while the belt mostly remains stationary when trying to make the droid turn.







While watching this, I did get an idea for how to cram in a tensioner without redoing the walls.  In the slot directly below the belt you can see one of the M5 bolts currently used to secure the front chassis to the rear chassis.  

Here's a side view.  The dashed lines are the approximate path of the outer edge of the belt.  The hole highlighted in blue holds the threaded insert that the M5 bolt in question goes into.


I could assign that hole double duty, using it to attach the tensioning idler (with a standoff that aligns the idler with the belt).  

I would need additional hardware after all.  Longer M5 screws for sure (exact length TBD by the design) and potentially some new bearings as well, depending on what type of screw serves as the axle for the idler (assuming it's not M4).

More problematically, space is tight. From the angle shown above, the constraints are that the idler has to avoid touching the yellow arm, which is the inboard support for the track bogies (easy to avoid since the belt needs to deflect in the other direction), and has to avoid contact with the green intermediate gear and the sprockets on the silver drive pulley (much harder to avoid)

Here it is from the front.


The standoff would be the same height as the pink mount in the image above, and the idler would extend to roughly the same height as the small pulley on the green intermediate stage.  

From the first image, it seems like only a narrow wedge of space is available, but as you can see in the bottom view below, there's a bit more room because the silver drive pulley is inset in places.



I'd need to have the mount stick out over the sprockets to use that space, though. Basically I'm imagining an L-shaped part, with the bottom of the L facing out from the center of the droid. M5 screws go through the tall part of the L into the highlighted hole. At the tip of the short end of the L is the axle mount for the idler.

My concern with this is whether the part would be strong enough to resist loosening or breaking when the belt is under tension. Also, I don't think there'd be much height left for the axle mount and bolt after clearing the sprocket.

So I suspect I'll only be able to use the wedge after all.

An alternate idea would be to print smaller belts (57 or 56 teeth). But they are already sort of a pain to install/remove as-is, and a smaller belt would be worse. Unlike the length of the belt, tensioners can be adjusted on the fly to increase slack.

An alternate slternate idea is to replace the belt with a chain. Unsure how feasible that is.