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Recently, I remembered that there was another option available for at least partially improving the belt situation: replace the primary belt and its pulleys with a pair of gears.
Just to explore the idea, I designed a pair of herringbone gears -- the green one for the brushless motor and the yellow one as a replacement for the larger part of the compound intermediate pulley. Assuming that these gears work well, that would leave only the 58T belt on each side, which means less things able to slip.
![[Image: 20230919-gear-meshing.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230919-gear-meshing.png)
The gears have the same gear ratio that the original pulleys had -- the green motor gear has 15 teeth, and the larger gear has 45, so 3:1. In the current droid, the motor shaft is 51.747 mm on center from the axle of the intermediate pulley. However, the geared version will need to sit closer -- meshing, in fact, which makes them 35mm on center.
That means I'll have to redesign the front side walls again to move the motor mount. To keep the gear diameters roughly similar to the pulleys they replace, I kept the module of these gears fairly low (1 mm). I might have to increase it if the gears aren't strong enough or they don't mesh precisely enough, and I'd have to change the side wall yet again.
As you can see in the CAD, there aren't any big issues with the parts interfering, though I might need to put a washer beneath the motor gear and lower its position accordingly (so that the black shaft part is less likely to contact the yellow gear at the edge nearest the motor). It's possible the secondary belt may rub the motor if it doesn't seat well, so I'll have to check that.
Currently, each intermediate pulley uses a pair of 623ZZ bearings, which are 10 mm OD, x 3 mm ID x 4 mm thick. As it happens, I've been working to upgrade the front axles and steering on the Baddeley Mouse droid to use M4 bolts, and as part of that design, I obtained a pack of MR104ZZ bearings. These bearings are 10 mm OD x 4 mm ID x 4 mm thick -- a drop-in replacement if I want to upgrade these pulley axles to M4 as well. (Another good reason to redesign the side plates.)
That sounds like a good idea to me. The belts put a lot of tension on the M3 hardware I currently use as pulley axles, but since there are two belts pulling in opposite directions, the net result is kind of a wash. With only one belt, the force would instead act unopposed in a single direction, which might be more likely to bend the axle. (M3 axles getting bent is one of the two big reasons I'm upgrading the Mouse droid to M4.)
Edit: And here is the new arrangement with the revised front outer side wall. I've put a recess for an M4 lock nut in the back of the wall, but the distance from the underside of the hex head to the outside of the yellow part is just under 50 mm, so 55 mm is likely the shortest bolt that will work.
![[Image: 20230920-new-front-outer.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/20230920-new-front-outer.png)
One drawback of this arrangement is that I'll once again lose my new easier belt installation option, and will instead have to take bits off.
As for the secondary belt, I can't really directly replace that one with gears, because the replacement for the integrated 42T pulley on the track's drive sprocket would need to be larger in diameter than the sprocket (and the track) in order to reach the smaller bit of the yellow part above. It might be doable with a gear train, but then the challenge would become finding a way to mount axles for the additional gear(s).
Oh, while I'm here, I decided to get an early start on a possible build for next Dragon Con... the OTHER D-O concept from Luke Fisher (third image here). After Dragon Con 2022, I considered doing this version for 2023, but there was a lot of doubt that I'd be able to build anything at all, and by the time I decided to, it was too late to start something that involved that much design work.
![[Image: concept-2-cad.png]](https://www.niflheim.net/droidbuilding/images/LD-F1/concept-2-cad.png)
This one is being done as a mod for the Baddeley v2 D-O (or at least what's in the Fusion file). No idea if or when I'll get further than just cosmetic CAD, but I will likely start a build thread if I do.
Just to explore the idea, I designed a pair of herringbone gears -- the green one for the brushless motor and the yellow one as a replacement for the larger part of the compound intermediate pulley. Assuming that these gears work well, that would leave only the 58T belt on each side, which means less things able to slip.
The gears have the same gear ratio that the original pulleys had -- the green motor gear has 15 teeth, and the larger gear has 45, so 3:1. In the current droid, the motor shaft is 51.747 mm on center from the axle of the intermediate pulley. However, the geared version will need to sit closer -- meshing, in fact, which makes them 35mm on center.
That means I'll have to redesign the front side walls again to move the motor mount. To keep the gear diameters roughly similar to the pulleys they replace, I kept the module of these gears fairly low (1 mm). I might have to increase it if the gears aren't strong enough or they don't mesh precisely enough, and I'd have to change the side wall yet again.
As you can see in the CAD, there aren't any big issues with the parts interfering, though I might need to put a washer beneath the motor gear and lower its position accordingly (so that the black shaft part is less likely to contact the yellow gear at the edge nearest the motor). It's possible the secondary belt may rub the motor if it doesn't seat well, so I'll have to check that.
Currently, each intermediate pulley uses a pair of 623ZZ bearings, which are 10 mm OD, x 3 mm ID x 4 mm thick. As it happens, I've been working to upgrade the front axles and steering on the Baddeley Mouse droid to use M4 bolts, and as part of that design, I obtained a pack of MR104ZZ bearings. These bearings are 10 mm OD x 4 mm ID x 4 mm thick -- a drop-in replacement if I want to upgrade these pulley axles to M4 as well. (Another good reason to redesign the side plates.)
That sounds like a good idea to me. The belts put a lot of tension on the M3 hardware I currently use as pulley axles, but since there are two belts pulling in opposite directions, the net result is kind of a wash. With only one belt, the force would instead act unopposed in a single direction, which might be more likely to bend the axle. (M3 axles getting bent is one of the two big reasons I'm upgrading the Mouse droid to M4.)
Edit: And here is the new arrangement with the revised front outer side wall. I've put a recess for an M4 lock nut in the back of the wall, but the distance from the underside of the hex head to the outside of the yellow part is just under 50 mm, so 55 mm is likely the shortest bolt that will work.
One drawback of this arrangement is that I'll once again lose my new easier belt installation option, and will instead have to take bits off.
As for the secondary belt, I can't really directly replace that one with gears, because the replacement for the integrated 42T pulley on the track's drive sprocket would need to be larger in diameter than the sprocket (and the track) in order to reach the smaller bit of the yellow part above. It might be doable with a gear train, but then the challenge would become finding a way to mount axles for the additional gear(s).
Oh, while I'm here, I decided to get an early start on a possible build for next Dragon Con... the OTHER D-O concept from Luke Fisher (third image here). After Dragon Con 2022, I considered doing this version for 2023, but there was a lot of doubt that I'd be able to build anything at all, and by the time I decided to, it was too late to start something that involved that much design work.
This one is being done as a mod for the Baddeley v2 D-O (or at least what's in the Fusion file). No idea if or when I'll get further than just cosmetic CAD, but I will likely start a build thread if I do.