some background: http://forums.reprap.org/read.php?177,767087,784083#msg-784083
and the same question here: https://physics.stackexchange.com/questions/352661/
can anyone help? basically - and i really should have done this before going ahead... *sigh*... - when you have a pulley system is the amount of force on the belt less, equal, or greater, under the same *print-head* acceleration conditions, compared to a *non* pulley system?
l.
Ok, so correct me if I am wrong but you are asking some mechanical questions.
so, I speak in general now and if you have question ask deeper.
Force needed to drive whatever you want to drive will be exactly the same at the end part of system. But efficiency of belt system could be slightly different then efficiency of `non` pulley system (whatever it is). But again, efficiency could be neglected for sake of easy of calculation or you can put around some value that (guess) could be 80-90%.
What you will be looking is gear ratio on pulley that could alter force/speed ratio and same thing on other system.
also, you will be looking on backlash.
On 19 August 2017 at 11:51, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
some background: http://forums.reprap.org/read.php?177,767087,784083#msg-784083
and the same question here: https://physics.stackexchange.com/questions/352661/
can anyone help? basically - and i really should have done this before going ahead... *sigh*... - when you have a pulley system is the amount of force on the belt less, equal, or greater, under the same *print-head* acceleration conditions, compared to a *non* pulley system?
l.
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On Sat, Aug 19, 2017 at 11:38 AM, Hrvoje Lasic lasich@gmail.com wrote:
Ok, so correct me if I am wrong but you are asking some mechanical questions.
mechanical / physics, yes.
so, I speak in general now and if you have question ask deeper.
Force needed to drive whatever you want to drive will be exactly the same at the end part of system.
on the print-head yes. but because of the doubled speed, the DRIVE end *NO*, the force is NOT the same.
But efficiency of belt system could be slightly different then efficiency of `non` pulley system (whatever it is). But again, efficiency could be neglected for sake of easy of calculation or you can put around some value that (guess) could be 80-90%.
i'm assuming that there are no significant losses around pulley bearings.
What you will be looking is gear ratio on pulley that could alter force/speed ratio and same thing on other system.
the gear ratio on a single pulley system is 2:1.
also, you will be looking on backlash.
*thinks*... backlash should be reduced (halved) due to the better effectiveness of the pulleys - assuming that there is no "play" in the bearings (we can assume decent bearings / idlers).
l.
below are answers
On 19 August 2017 at 12:52, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Sat, Aug 19, 2017 at 11:38 AM, Hrvoje Lasic lasich@gmail.com wrote:
Ok, so correct me if I am wrong but you are asking some mechanical questions.
mechanical / physics, yes.
so, I speak in general now and if you have question ask deeper.
Force needed to drive whatever you want to drive will be exactly the same at the end part of system.
on the print-head yes. but because of the doubled speed, the DRIVE end *NO*, the force is NOT the same.
so, if on the print head-side force is the same then it is on the drive side same as well (work can not be missing somewhere). However, if you are doubling the speeds, then overall work required will be some higher value so, correct would be to say that because of double speed you are having more force on print head needed and as result drive will also have to work more, losses will be bigger etc.
anyway, that is all theoretical. Real value would be to find out force you need to have on print head then do some sort of calculation back to the drive. I guess you don't know that but maybe you can see what has been done on system that have other drive and then try to extrapolate what you will need. We can also assume here that someone has already put some reserve on what is now there, so possibly you can leave same motor or if you have problem increase force at disposal assuming you can do that on same motor size (nema 17 or so)
I think backlash here will be your biggest problem here. Backlash is in fact inertia of the system. So, for example when you run you want to stop you cant do it right away, you need some time/distance. Or comparing to electrical engineering you can compare it to inductance. Inductance is resistance plus reactance.
You said that you expect lesser backlash on pulley system. If that is the case (I am not sure why or why not this statement would be truth) you will be able to increase speed up to certain point but you will have to test where is that point. Basically you will have to do a lot of testing.
But efficiency of belt system could be slightly different then efficiency of `non` pulley system (whatever it is). But again, efficiency could be neglected for sake of easy of calculation or
you
can put around some value that (guess) could be 80-90%.
i'm assuming that there are no significant losses around pulley bearings.
What you will be looking is gear ratio on pulley that could alter force/speed ratio and same thing on other system.
the gear ratio on a single pulley system is 2:1.
also, you will be looking on backlash.
*thinks*... backlash should be reduced (halved) due to the better effectiveness of the pulleys - assuming that there is no "play" in the bearings (we can assume decent bearings / idlers).
l.
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On Sat, Aug 19, 2017 at 3:00 PM, Hrvoje Lasic lasich@gmail.com wrote:
below are answers
On 19 August 2017 at 12:52, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Sat, Aug 19, 2017 at 11:38 AM, Hrvoje Lasic lasich@gmail.com wrote:
Ok, so correct me if I am wrong but you are asking some mechanical questions.
mechanical / physics, yes.
so, I speak in general now and if you have question ask deeper.
Force needed to drive whatever you want to drive will be exactly the same at the end part of system.
on the print-head yes. but because of the doubled speed, the DRIVE end *NO*, the force is NOT the same.
so, if on the print head-side force is the same then it is on the drive side same as well (work can not be missing somewhere). However, if you are doubling the speeds, then overall work required will be some higher value
doubling the speed of the *belt* but not the print-head. we're comparing like-for-like scenario (pulleys / no-pulleys).
btw benson kindly answered on the forum (thank you!) and i think i have a handle on the situation now.
so, correct would be to say that because of double speed you are having more force on print head needed and as result drive will also have to work more, losses will be bigger etc.
no, the speed of the print-head should be the same in both scenarios (pulleys / no-pulleys) therefore the force should be the same.
now, what benson kindly pointed out is that in a pulley system the force is *SHARED* between the two belt segments, therefore the amount of "stretch" (which is what i was concerned about) should also be HALVED compared to a non-pulley system.
where i got confused was, i thought that the belt's actual travel speed was somehow involved in the equation: it would be.... *if* the belt's mass was significant.
I think backlash here will be your biggest problem here. Backlash is in fact inertia of the system. So, for example when you run you want to stop you cant do it right away, you need some time/distance. Or comparing to electrical engineering you can compare it to inductance. Inductance is resistance plus reactance.
indeed. so, because the force is halved (for the same speed compared to a non-pulley system) we *should* also get less backlash as well. yay.
You said that you expect lesser backlash on pulley system. If that is the case (I am not sure why or why not this statement would be truth) you will be able to increase speed up to certain point but you will have to test where is that point. Basically you will have to do a lot of testing.
indeed :) the aim is to use the extra wiggle-room (less backlash, less load) to increase speed by some factor... probably not double but a good fraction of that, and see what happens.
certainly someone pointed out that the speed of the NEMA17s, when you go faster, you actually get less torque. whoops. and the rated maximum seems to be around 1800 mm / sec. at that point you get *significantly* less torque.
so it's not going to be a straightforward "go twice as fast" thing.
l.
certainly someone pointed out that the speed of the NEMA17s, when you go faster, you actually get less torque. whoops. and the rated maximum seems to be around 1800 mm / sec. at that point you get *significantly* less torque.
so, when you say nema 17 you refer to dimensions of the motor, not torque. it is some American standard,so nema 17 refer to 43.2 mmx 43.2 mm if you look at face of motor. But you can have different torques at same size of the motor. They increase the size of the motor in length. so you will be still able to alter torque to some extent no matter speed. Keep in mind that you are flexible here up to certain point. After that, if you need more torque you go to next bigger size of motor nema 23 or so.
so it's not going to be a straightforward "go twice as fast" thing.
for sure not otherwise you would see some speeds as standard. My guess is that what you have on market is pretty much optimized per cost/performance but you may well be more efficient for your particular case.
l.
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On Sat, Aug 19, 2017 at 3:34 PM, Hrvoje Lasic lasich@gmail.com wrote:
so, when you say nema 17 you refer to dimensions of the motor, not torque.
yes. they're common enough that they're quite low-priced.
look at face of motor. But you can have different torques at same size of the motor.
yes. for the purposes of the analysis (pulley / non-pulley) we assume exact same motor.
They increase the size of the motor in length. so you will be still able to alter torque to some extent no matter speed. Keep in mind that you are flexible here up to certain point. After that, if you need more torque you go to next bigger size of motor nema 23 or so.
yes. that also increases cost, and weight, not just the motor size but also the holders, and also the ampage needed of the controller. which again increases cost. so, trying not to do that as it's not necessary.
l.
On Sat, 19 Aug 2017 15:47:26 +0100 Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
On Sat, Aug 19, 2017 at 3:34 PM, Hrvoje Lasic lasich@gmail.com wrote:
They increase the size of the motor in length. so you will be still able to alter torque to some extent no matter speed. Keep in mind that you are flexible here up to certain point. After that, if you need more torque you go to next bigger size of motor nema 23 or so.
yes. that also increases cost, and weight, not just the motor size but also the holders, and also the ampage needed of the controller. which again increases cost. so, trying not to do that as it's not necessary.
l.
Or you could use two nema 17's on one pulley. Mind, I don't know how you designed the pulley system so this might be rather difficult or really easy.
Sincerely, David
On Tue, Aug 22, 2017 at 10:43 PM, David Niklas doark@mail.com wrote:
Or you could use two nema 17's on one pulley. Mind, I don't know how you designed the pulley system so this might be rather difficult or really easy.
yyeah... trying that would have me concerned. more tomorrow. 2am now.
l.
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David Niklas -
Hrvoje Lasic -
Luke Kenneth Casson Leighton