idea for linear belt drive

[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

[Robin Hewitt]

250rpm is doable IMHO

You are probably right. Stepper technology has moved on and I need to adjust my comfort zone.

My comfort zones are fairly well tuned, I always 'know' what thickness of material to use, what bolt size etc. But obviously I must now consider adjusting my stepper motor zone, possible my feed rate zone to. This will require a degree of experimentation.

I have had over 1000 rpm on a disc-magnet stepper and a 40 volt driver but that is one whacky stepper motor.

[HiltonSteve]

Here is another idea which i quite like for linear drive, watch the video which shows the machine using chain and belt. I like the idea of keeping the chain/belt stationary and pulling the axis along on it.

http://www.youtube.com/watch?v=vETkf...mbedded#at=154

You are probably right. Stepper technology has moved on and I need to adjust my comfort zone.

I have had over 1000 rpm on a disc-magnet stepper and a 40 volt driver but that is one whacky stepper motor.

My machine runs the steppers at 1000rpm for rapids and even had it up 1500rpm at one point but was just too fast for the machine. I am using Roy's 5A driver boards and 5A steppers, had to keep the boards cool to get these speeds with a couple of 120mm fans but no problems so far!