idea for linear belt drive

[Robin Hewitt]

Is a 10 tooth pulley big enough to hold the belt on a quarter turn? That's 2 teeth.

Is it small enough to get any kind of resolution on a stepper?

A 15mm PCD pulley moves it 47mm per rev.

0.12 mm/step before you start springy microstepping, will that work for cutting alloy?

If you microstep can you rattle the PUL pin on the driver fast enough to get the top speed?

If you gear it down, do you move beyond the top speed of the motor?

Beginners don't usually play with the numbers, they just look for massive torque motors and hope that will make it right. That's why steppers are usually sold by the Newton meter rather than by the torque to speed graph.

130kg belt tension may exceed the permitted side loading on the motor shaft.

Can you actually get a big enough shaft inside a 15mm aluminium pulley without severely under cutting the teeth? I think you will need a bearing either side of it.

A little maths and understanding to find the best compromise before you build can save a lot of disappointment later. (Please assume a big grin smiley, the new editor restricts my smiley selection, sometimes it shows, sometimes it doesn't).

[irving2008]

Is a 10 tooth pulley big enough to hold the belt on a quarter turn? That's 2 teeth.
I was assuming that both pulleys on the shaft were driving, thats 4 teeth and the torque is fine on that...

Is it small enough to get any kind of resolution on a stepper?

A 15mm PCD pulley moves it 47mm per rev.

0.12 mm/step before you start springy microstepping, will that work for cutting alloy?
Probably not, but I don't think you would realistically do alloy on an 8 x 4 router

If you microstep can you rattle the PUL pin on the driver fast enough to get the top speed?
Needs 200rpm for rapids, thats fullstep = 670steps/sec, then microstep for final positioning... needs a morphing driver really but its doable at fixed microstepping 2600steps/sec.

If you gear it down, do you move beyond the top speed of the motor?

Beginners don't usually play with the numbers, they just look for massive torque motors and hope that will make it right. That's why steppers are usually sold by the Newton meter rather than by the torque to speed graph.

130kg belt tension may exceed the permitted side loading on the motor shaft.
It would, thats why it needs the pulleys on a bearing supported shaft (skate bearings OK to 1700N radial force) and the motor coupled in.


Can you actually get a big enough shaft inside a 15mm aluminium pulley without severely under cutting the teeth? I think you will need a bearing either side of it.
Thats an interesting one, and not one I'd considered. The standard 10tooth pulley is a 6mm dia shaft. the upper pulley and lower pulley are in opposing tension so can a 6mm shaft stand a shear force in the middle of 2600N?
I suspect it will need a bigger (more teeth) pulley and the motor will need to be geared down to drive the shaft to get the resolution without too much microstepping. A 20th tooth pulley and a 2.5:1 gearing would give a 30mm dia pulley (good for a 10 or 12mm shaft). One turn of the pulley = 100mm so 0.1mm resolution needs 1000steps, geared down 2.5:1 is 400steps/rev which is 1/2stepping and 10m/min rapids = 100rpm of pulley = 250rpm of motor which is still feasible at 1666steps/sec.

A little maths and understanding to find the best compromise before you build can save a lot of disappointment later. (Please assume a big grin smiley, the new editor restricts my smiley selection, sometimes it shows, sometimes it doesn't).

mine doesnt! :naughty:

[dickieto]

Is a 10 tooth pulley big enough to hold the belt on a quarter turn? That's 2 teeth.

Is it small enough to get any kind of resolution on a stepper?

A 15mm PCD pulley moves it 47mm per rev.

0.12 mm/step before you start springy microstepping, will that work for cutting alloy?

If you microstep can you rattle the PUL pin on the driver fast enough to get the top speed?

If you gear it down, do you move beyond the top speed of the motor?

Beginners don't usually play with the numbers, they just look for massive torque motors and hope that will make it right. That's why steppers are usually sold by the Newton meter rather than by the torque to speed graph.

130kg belt tension may exceed the permitted side loading on the motor shaft.

Can you actually get a big enough shaft inside a 15mm aluminium pulley without severely under cutting the teeth? I think you will need a bearing either side of it.

A little maths and understanding to find the best compromise before you build can save a lot of disappointment later. (Please assume a big grin smiley, the new editor restricts my smiley selection, sometimes it shows, sometimes it doesn't).

hi robin
looks like i will need to go back to school,maths was never my strongest subject
i was thinking more along the lines of a 40mm pulley!!!.and driving the stepper with a reduction to the shaft.would this work or would the stepper be running to fast when the ganty is moving at high speed
as you have said i am just a beginner and speed,torque,force applied etc are all new to me.
i was thinking of making a prototype using chains and sprockets (my works got plenty)just to try out the theory,measuring pull needed to turn drive shaft with spring scales!!
thanks for your input
Tom

[irving2008]

hi robin
looks like i will need to go back to school,maths was never my strongest subject
i was thinking more along the lines of a 40mm pulley!!!.and driving the stepper with a reduction to the shaft.would this work or would the stepper be running to fast when the ganty is moving at high speed
as you have said i am just a beginner and speed,torque,force applied etc are all new to me.
i was thinking of making a prototype using chains and sprockets (my works got plenty)just to try out the theory,measuring pull needed to turn drive shaft with spring scales!!
thanks for your input
Tom

Tom,

See the inline answer I gave to Robin's questions. He is quite right, there is the 'suck it and see' approach or the 'model and calculate' approach (and then usually an element of suck it and see!) - with something this complex its worth spending some time getting a basic appreciation of the numbers to try and see if things look reasonable...

If you want a more detailed description of the torque/forces/etc to help you understand the number just ask...

A 40mm PCD dia pulley is approx 120mm circumference (24 tooth). Therefore 1 rev moves 120mm. Set 1 rev = 1200steps then 1 step = 0.1mm. At 10m/min rapid the pulley turns at 10,000/120 = 83.33rpm, geared down 3:1 (12teeth/36teeth) the motor turns three times as fast = 3 x 83.33 = 250rpm, in 1/2step mode this is 250/60 * 400 = 1667 steps/sec which is no problem.

[Robin Hewitt]

the motor turns three times as fast = 3 x 83.33 = 250rpm

That's over 4 revs/second. If we start straying beyond the capabilities of the cheapy 40 volt stepper drivers he needs to be warned, but maybe we have already confused him enough for one day

Thanks for fixing my smilies

[ptjw7uk]

The first part of my router design arrived today a 4.4m drive belt for £6 cant be bad but the teeth on the belt are not uniform so will not lay back on itself in the the teeth are larger than the gaps.
Oh well back to the drawing board it may do for the design on this thread.
The belt is designated as RPD8 the 8 I assume is the tooth root, tried a search but nothing I could recognise but cheap enough.
Now for some pulleys.

peter

[dickieto]

The first part of my router design arrived today a 4.4m drive belt for £6 cant be bad but the teeth on the belt are not uniform so will not lay back on itself in the the teeth are larger than the gaps.
Oh well back to the drawing board it may do for the design on this thread.
The belt is designated as RPD8 the 8 I assume is the tooth root, tried a search but nothing I could recognise but cheap enough.
Now for some pulleys.

peter

hi peter
what width is your belt and is there any more available???:naughty:
at £6 it might just be worth giving my idea a go:dance:
tom

[irving2008]

That's over 4 revs/second. If we start straying beyond the capabilities of the cheapy 40 volt stepper drivers he needs to be warned, but maybe we have already confused him enough for one day

Thanks for fixing my smilies

Robin,

I get 300rpm on my crappy 10mH Astrosyn steppers and a simple L297/298 driver. Admittedly thats as fast as it will go, but they still generate a measured 0.45Nm of torque at that speed!

250rpm is doable IMHO

Irving...

ps, you're welcome

[ptjw7uk]

Had a look this morning and last one has sold.
Sorry
Still to find pitch and get pulleys
Peter

[dickieto]

Had a look this morning and last one has sold.
Sorry
Still to find pitch and get pulleys
Peter

hi peter
i have just bought 2 of the same belt from epay(thanks to john for posting the link for item on ebay,tried to reply my thanks but his post has now disappeared?!!!)
they were a bargain only £0.99 each,sadly postage was £5.99 each:nope: oh well cant have it both ways.
another step closer to my build.
Tom