A different way cover

[RJSakowski]

A spring mechanism would not provide "constant torque". I am fine with over thinking stuff.

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[NC Rick]

Also, a counterweight would require a reduction mechanism or a fairly deep hole in the ground for my application.

 

[NC Rick]

See, this kind of banter leads to learning stuff. I may order one just to play with it!

 

[Winegrower]

Well, an interesting idea. Following your “concept”, how about choose a DC motor with the right torque constant, no gear train, no pwm controller, just a constant current source to maintain desired torque. This is how some devices maintain tension on mag tapes, for example.

But really, I have never felt a need for way covers. Or pocket protectors, car bras, etc.

 

[benmychree]

Well, an interesting idea. Following your “concept”, how about choose a DC motor with the right torque constant, no gear train, no pwm controller, just a constant current source to maintain desired torque. This is how some devices maintain tension on mag tapes, for example.

But really, I have never felt a need for way covers. Or pocket protectors, car bras, etc.

My sentiments, exactly!

 

[benmychree]

It seems to me that way covers always allow crud to accumulate underneath where it can't be seen, and cause damage unobserved. When I worked at Kaiser Steel, we retrofitted a bunch of old planers with milling heads using 24" and smaller carbide insert face mills to mill various weld preps and to finish to width and with caulking grooves, the tunnel liner segments for BART in the SF bay area for the underground parts of the system, they made way covers that rolled up, made of cloth inserted rubber; what happened, when they rolled up, the stuff on top transferred to the underside, dropped off and got onto the way surfaces and caused a lot of damage which was not repaired, when the job was finished, most all the machinery was scrapped -----

 

[homebrewed]

It seems to me that way covers always allow crud to accumulate underneath where it can't be seen, and cause damage unobserved. When I worked at Kaiser Steel, we retrofitted a bunch of old planers with milling heads using 24" and smaller carbide insert face mills to mill various weld preps and to finish to width and with caulking grooves, the tunnel liner segments for BART in the SF bay area for the underground parts of the system, they made way covers that rolled up, made of cloth inserted rubber; what happened, when they rolled up, the stuff on top transferred to the underside, dropped off and got onto the way surfaces and caused a lot of damage which was not repaired, when the job was finished, most all the machinery was scrapped -----

Perhaps that's an unintended "benefit" of using mylar -- it's transparent!

 

[homebrewed]

Well, an interesting idea. Following your “concept”, how about choose a DC motor with the right torque constant, no gear train, no pwm controller, just a constant current source to maintain desired torque. This is how some devices maintain tension on mag tapes, for example.

But really, I have never felt a need for way covers. Or pocket protectors, car bras, etc.

A constant current generator will generate heat, unlike the switch(es) in a PWM controller. I initially considered a constant current source but decided a cheap PWM controller would suffice, without the need to worry about power dissipation in the controller.

I agree that a big enough DC motor could be direct coupled. If I find one for a reasonable price I'll give it a shot. However, it will be hard to beat the $3 motor I've got in there right now. BLDC motors can be very powerful for the money, but ESC's aren't suited for this kind of application. Maybe a sensored BLDC motor + an Arduino? Now it gets even more Rube-Goldberg-ish. And sensored BLDC's cost more.

 

[benmychree]

Perhaps that's an unintended "benefit" of using mylar -- it's transparent!

Transparent for how long?

 

[NC Rick]

A constant current generator will generate heat, unlike the switch(es) in a PWM controller. I initially considered a constant current source but decided a cheap PWM controller would suffice, without the need to worry about power dissipation in the controller.

I agree that a big enough DC motor could be direct coupled. If I find one for a reasonable price I'll give it a shot. However, it will be hard to beat the $3 motor I've got in there right now. BLDC motors can be very powerful for the money, but ESC's aren't suited for this kind of application. Maybe a sensored BLDC motor + an Arduino? Now it gets even more Rube-Goldberg-ish. And sensored BLDC's cost more.

Go old school man, use a micro-switch with a lightweight arm extension mounted on the saddle that becomes activated by the mylar cover being under tension (using the N.C. contacts) to power the motor.