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03-27-2022, 10:34 PM
I've continued working on the drive system. I think I settled on the 12.6:1 given by the 42 tooth pulley mentioned last time. I've also been planning mounts, axles for the rollers, and the supports that I mentioned last time.
Speaking of the rollers, I knew all along that Treadwell's ... well, treads ... use a centering mechanism, and I also saw that Paul recently converted his to effectively become synchronous timing belts. I recently started getting to the point where I needed to look at this for LD-F1.
That's when I realized I might have a problem finding a tooth pitch that would work with both the roller diameter and wheelbase I chose.
The crux of the matter is that the roller circumference and the tread circumference are both functions of Pi (an irrational number), so neither are rational numbers, much less integers. Finding any tooth count that would divide evenly into both numbers seemed unlikely (it has to divide more or less evenly, because you can't have partial teeth). Either the roller diameter or the wheelbase would have to be adjusted until I found something with minimal difference between the pitches.
Eventually, I ended up making a spreadsheet so I could play with the values to find something that worked. I'm going to limit the values below to 6 digits of precision.
If I increased the wheelbase by 2.158 mm to 408.558 mm (so 16.085 inches), then I get a Tread Circumference of 1136.301814 mm. (Roller Circumference wasn't changed, it remains 319.185813 mm.)
If I put 25 teeth on the roller and 89 on the tread, then that gives me a roller pitch of 12.767433 mm and a tread pitch of 12.767436 (both around half an inch) -- a difference of 0.000004 mm per tooth. If I multiply that by the number of teeth, then the roller has an overall error of 0.000089 mm, and the tread's total error is 0.000317 mm.
Those numbers are all well below the accuracy of the printer, which for my printer is 0.0125 mm in X & Y (and 0.0020 in Z). So I don't see much point in trying to optimize any further.
There's another concern, which is whether the pitch chosen will affect the flexibility of the tread. I can reduce that by doubling the number of teeth on both roller (to 50) and tread (178), which halves the pitch to a bit over 6 mm. The error is also halved, but overall that doesn't change anything, since it's applied to twice as many teeth.
In the physical world, I printed a couple of test pulleys for the drive and also got a new set of ESCs for the iFlyRC motors. I hooked these up to one of my ESP32 boards, with Penumbra installed for testing. It worked pretty well. With the battery fully charged, I'd be getting more RPM out of it. I only show one motor/esc here, mostly because I don't currently have an XT60 splitter to supply battery power to both ESCs at once and didn't feel like making one.
The timing pulleys shown on the motors here are the equivalent of the green one in the screenshots from the previous post, just with different attachment mechanisms.
(More in a moment; the forum will only allow one video per post.)
Speaking of the rollers, I knew all along that Treadwell's ... well, treads ... use a centering mechanism, and I also saw that Paul recently converted his to effectively become synchronous timing belts. I recently started getting to the point where I needed to look at this for LD-F1.
That's when I realized I might have a problem finding a tooth pitch that would work with both the roller diameter and wheelbase I chose.
The crux of the matter is that the roller circumference and the tread circumference are both functions of Pi (an irrational number), so neither are rational numbers, much less integers. Finding any tooth count that would divide evenly into both numbers seemed unlikely (it has to divide more or less evenly, because you can't have partial teeth). Either the roller diameter or the wheelbase would have to be adjusted until I found something with minimal difference between the pitches.
Eventually, I ended up making a spreadsheet so I could play with the values to find something that worked. I'm going to limit the values below to 6 digits of precision.
If I increased the wheelbase by 2.158 mm to 408.558 mm (so 16.085 inches), then I get a Tread Circumference of 1136.301814 mm. (Roller Circumference wasn't changed, it remains 319.185813 mm.)
If I put 25 teeth on the roller and 89 on the tread, then that gives me a roller pitch of 12.767433 mm and a tread pitch of 12.767436 (both around half an inch) -- a difference of 0.000004 mm per tooth. If I multiply that by the number of teeth, then the roller has an overall error of 0.000089 mm, and the tread's total error is 0.000317 mm.
Those numbers are all well below the accuracy of the printer, which for my printer is 0.0125 mm in X & Y (and 0.0020 in Z). So I don't see much point in trying to optimize any further.
There's another concern, which is whether the pitch chosen will affect the flexibility of the tread. I can reduce that by doubling the number of teeth on both roller (to 50) and tread (178), which halves the pitch to a bit over 6 mm. The error is also halved, but overall that doesn't change anything, since it's applied to twice as many teeth.
In the physical world, I printed a couple of test pulleys for the drive and also got a new set of ESCs for the iFlyRC motors. I hooked these up to one of my ESP32 boards, with Penumbra installed for testing. It worked pretty well. With the battery fully charged, I'd be getting more RPM out of it. I only show one motor/esc here, mostly because I don't currently have an XT60 splitter to supply battery power to both ESCs at once and didn't feel like making one.
The timing pulleys shown on the motors here are the equivalent of the green one in the screenshots from the previous post, just with different attachment mechanisms.
(More in a moment; the forum will only allow one video per post.)