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dickieto
19-01-2010, 03:59 AM
hi everyone:toot:
just thought i'd share an idea for a belt driven linear gantry on a large router table
i was going with belts to keep cost down as the wife doesn't know what i am up to yet:naughty:
just an idea running around in my head as i am trying to gather up parts just now
has any one any thoughts on it?
do you think there would be to much drag on the stepper motor
sorry for the crappy autocad drawings!!:redface:
:beer: Tom

BillTodd
19-01-2010, 01:46 PM
That is a very good idea (wished I'd thought of it :)) Reminds me of Mike Everman's servo belt idea (http://www.cnczone.com/forums/showthread.php?t=59570)(worth reading for belt info)

You'll probably need to gear down the drive from the stepper/servo to the drive belt to get the desired resolution. And, make sure the belt you choose has sufficient tooth strength to put up with the dynamic load.

I like it .

[edit] This is dickieto's idea for those of you without a dxf viewer:

Ross77
19-01-2010, 08:34 PM
Sweet. Thats so simple, unless I'm reading it wrong. Is that in plan with the belts running through the y axis?

Vic66
19-01-2010, 09:13 PM
I like the look of your idea to, could possibly use chain and sprockets ?

dickieto
19-01-2010, 09:20 PM
That is a very good idea (wished I'd thought of it :)) Reminds me of Mike Everman's servo belt idea (http://www.cnczone.com/forums/showthread.php?t=59570)(worth reading for belt info)

You'll probably need to gear down the drive from the stepper/servo to the drive belt to get the desired resolution. And, make sure the belt you choose has sufficient tooth strength to put up with the dynamic load.

I like it .

[edit] This is dickieto's idea for those of you without a dxf viewer:

thanks bill,how do you change autocad drawings into something everyone can see?
i tried for ages to upload these drawings!:rolleyes:

irving2008
19-01-2010, 09:26 PM
its the same idea that was documented here (http://www.cnczone.com/forums/showthread.php?t=51485)to avoid racking when usiing one leadscrew offset from centre. The neat idea here is to make it the drive mechanism too... and I've not seen that before! The great thing about this is the pulleys at each end run in the same direction and in sync, so this works as a drive mechanism. 15 or 20mm belts can take some punishment, so it could work well....

BillTodd
19-01-2010, 09:36 PM
,how do you change autocad drawings into something everyone can see?

Export as bmp then use Serif PhotoPlus to convert to JPG

dickieto
19-01-2010, 09:36 PM
Sweet. Thats so simple, unless I'm reading it wrong. Is that in plan with the belts running through the y axis?

thanks ross :smile:
my plan is to build router that can take 8x4 sheets so the belts would run full length of table crossing over gantry to other side,both being driven by toothed gear reduced down from stepper motor then the back of the belts would go round idler then down the other side of router. Hope that kind of makes sense:confused:
I wish i could just draw a bit faster and better but am just learning autocad:redface:

dickieto
19-01-2010, 09:52 PM
its the same idea that was documented here (http://www.cnczone.com/forums/showthread.php?t=51485)to avoid racking when usiing one leadscrew offset from centre. The neat idea here is to make it the drive mechanism too... and I've not seen that before! The great thing about this is the pulleys at each end run in the same direction and in sync, so this works as a drive mechanism. 15 or 20mm belts can take some punishment, so it could work well....

thanks once again irving.
I use to work on a machine years ago,that worked very similarly but with wire ropes, which pulled a sledge down a passage that feed cattle.
great what you think of when looking for cheaper alternatives than racks or ballscrews:naughty:
do you think that the belts would deflect(bounce) to much on travel over 8 ft?

irving2008
20-01-2010, 12:35 AM
Some thoughts:
big bed so want reasonable rapids, say 10m/min (traverse 8' in 15sec) and 3m/min cutting speed max.
assume 25kg gantry

Force(friction) = mass * g * friction coeef = 25 * 10 * .01 (skate bearings) = 2.5N

Force(accel) = mass * acceleration. Assume acceleration time for rapids = 0.5sec = 0.5m/sec^2, cutting =0.1sec = 0.33m/sec^2 so take accel = 0.5m/s^2 then force = 25 * 0.5 = 12.5N

Cutting force for wood, say 10N max

Therefore force on belt = 2.5 + 12.5 + 10 = 25N, design for 50N cutting, 30N rapids (actually spilt equally between red and white belts)

pitch of HTD belt = 5mm = 2000teeth/min rapids, for 10t pulley = 200rpm, 60rpm for cutting. 200rpm = 666 fullsteps/sec
Requred resolution = 0.1mm, 1 turn of pulley=50mm so need 500steps/rev = 1/4step microstepping.

design torque = 50N @ 7.5mm radius (10t pulley) = 0.38Nm @ 60rpm, 0.23Nm @ 200rpm... a 1Nm motor should acheive this.

Peak torque on 25mm wide 5mm pitch HTD belt is 34N, but this is split between two belts so should be OK. If not will have to go to a wider belt.. Several suppliers, such as Gates-Europe, do HTD5 belts in open-ended style up to 150mm wide but you'd have to make your own pulleys above 25mm.

Belt tension required is around 130kgf

Belt data from gates-europe and spd. However open-ended belting is only available in 100m rolls, so this might not be as cheap as you might think!

dickieto
20-01-2010, 01:21 AM
:eek: slow down a bit irving!! it will take me all night to take all that info in!!!:confused:
only joking, thanks for the calculations.
does this mean i could fit the 10 toothed pulley directly onto stepper motor with out reduction?or am i missing something,i would like to go for bigger motor just incase i was going to do some alloy or do you think this would just be overkill??
i was also thinking of making my own v bearings with twin bearings inside round bar turned down to suit angle iron or do you think this would be to much friction??
sorry for all the questions but its your own fault for being so knowledgable!!:joker::naughty:
thanks again Tom

Ross77
20-01-2010, 02:13 AM
my plan is to build router that can take 8x4 sheets so the belts would run full length of table crossing over gantry to other side,both being driven by toothed gear reduced down from stepper motor then the back of the belts would go round idler then down the other side of router. Hope that kind of makes sense:confused:
I wish i could just draw a bit faster and better but am just learning autocad:redface:


Understood perfectly. Have you priced it up tho? as Irving said belts arnt that cheap espesially as you'll need them 12' or more in one run as it also goes thro the Y axis. :eek:

I think that once you get to 8'x4' belts arnt a cheap option, just cheaper than ball screws :smile:

I wouldnt have thought belt sagg would be to much of a problem as they will be on their side, and if you use collar less pulleys you could put a small ledge for the belt to sit on.

If you make our own Vee bearing will you save that much? Have a word with vic66, hes using vee bearings and angle, look at his thread and theres a link to the mechmate stuff which sounds simillar to what you want.

irving2008
20-01-2010, 08:23 AM
:eek: slow down a bit irving!! it will take me all night to take all that info in!!!:confused:
only joking, thanks for the calculations.
does this mean i could fit the 10 toothed pulley directly onto stepper motor with out reduction?or am i missing something,i would like to go for bigger motor just incase i was going to do some alloy or do you think this would just be overkill??
i was also thinking of making my own v bearings with twin bearings inside round bar turned down to suit angle iron or do you think this would be to much friction??
sorry for all the questions but its your own fault for being so knowledgable!!:joker::naughty:
thanks again Tom


dont take these as gospel, its a frst cut. I may have missed something, or my approach to estimating how forces giving rise to motion of the gantry translates to torque might be wrong. I dont want to diss your idea, but can't help but think if it was that easy why hasn't someone done it before? I do think the limiting factor might be belt width/torque handling and availability in the lengths you need. One or two suppliers do continuous belts larger than 3.7m which could be cut open, but these tend to be in the 8mm not 5mm HTD and the pricing is >50 per belt. With 8mmHTD a 10t pulley is 25mm dia so the torque needed at 200rpm is 0.3Nm, and the resolution at 1/4step is 0.1mm. 8mm belts come standard at 30 and 50mm widths

I was working on the assumption that the steppers drive the pulleys directly, but in practice you can't because the shaft length is too short. You will need the two drive pulleys mounted on a shaft in bearings which is driven by the motor via a coupling.

Before embarking on the big build, I would trial a small version of the X say 200 or 300mm square using 5mmHTD and cheap drawer slides from B&Q to measure the loads/forces/etc. operating load could be added by a bit of string running over a pulley to a pan that can be filled with sand or other stuff to see how it performs under load.

BillTodd
20-01-2010, 01:57 PM
However open-ended belting is only available in 100m rolls, so this might not be as cheap as you might think!

A grovelling appeall to the afore mentioned Mike Everman might be worth a try :)

Robin Hewitt
21-01-2010, 12:31 PM
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
21-01-2010, 01:41 PM
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
21-01-2010, 02:29 PM
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:rolleyes:
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
:smile:Tom

irving2008
21-01-2010, 04:01 PM
hi robin
looks like i will need to go back to school,maths was never my strongest subject:rolleyes:
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
:smile: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
21-01-2010, 04:48 PM
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 :smile:

Thanks for fixing my smilies :beer:

ptjw7uk
21-01-2010, 07:33 PM
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
21-01-2010, 11:25 PM
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
22-01-2010, 11:56 AM
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 :smile:

Thanks for fixing my smilies :beer:


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 :smile:

ptjw7uk
22-01-2010, 12:03 PM
Had a look this morning and last one has sold.
Sorry
Still to find pitch and get pulleys
Peter

Robin Hewitt
22-01-2010, 12:48 PM
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
22-01-2010, 02:34 PM
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=vETkf1sqo3M&feature=player_embedded#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!

Robin Hewitt
22-01-2010, 03:15 PM
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.

Aha! You to have a comfort zone :heehee:

I have the 220 Volt drivers so presumably it should go like the absolute clappers once I get the 48MHz dedicated cpu rattling the driver pins.

Thinks: Max step rate 40Khz, divide by 1600 steps/rev, 25 rps, 1500 rpm, 10cm/second rapids resolving 2.5 microns :eek:

No, I'm not brave enough either :rofl:

HiltonSteve
22-01-2010, 05:51 PM
Aha! You to have a comfort zone :heehee:


Seems that i do without even realising..!! :rofl:

dickieto
22-01-2010, 11:39 PM
Had a look this morning and last one has sold.
Sorry
Still to find pitch and get pulleys
Peterhi peter
i have just bought 2 of the same belt from epay:yahoo:(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.
:beer:Tom

ptjw7uk
23-01-2010, 10:44 AM
Only problem now is to find the pulleys or drawing of wht is listed as an RPD8 belt. Nearest I have found is listed as RPP but no drawings so I can compare.
Good score on the belts.

Peter

irving2008
23-01-2010, 07:15 PM
Peter, I too did a quick scan. No info on RPD either. Maybe you can draw up the profle so we can compare it to HTD8?

ptjw7uk
23-01-2010, 07:40 PM
Nearest that I have found is HTS this is for a RPP profile http://www.martinsprocket.com/2001/SecKb.pdf#J74 will do some measurements when I go down to the workshop.
Peter

dickieto
24-01-2010, 01:21 AM
Nearest that I have found is HTS this is for a RPP profile http://www.martinsprocket.com/2001/SecKb.pdf#J74 will do some measurements when I go down to the workshop.
Peter
please let us know what u come up with!!
thanks again tom.

ptjw7uk
24-01-2010, 01:09 PM
Tried to measure teeth but the bottom section is radiused about 3mm, so not easy to measure. Taking a resin cast at the moment to to get better measurements. Definately 8mm pitch about 25.6mm wide looking like a HTS pulley might be the one but not found any measurements to caompare to.

peter

irving2008
24-01-2010, 02:31 PM
According to Gates, RPP belts will run interchangably on RPP or standard HTD profile pulleys. The main difference it would seem is that the RPP profile has a dent on the top of the tooth to reduce wear and allow the tooth to sit deeper increasing the transmission properties. Are there any markings on the belt itself? Here's (http://www.megarubber.com/modules.php?op=modload&name=Downloads&file=index&req=getit&lid=1)a PDF with tooth dimensions for a specific brand.

boldford
10-09-2012, 10:44 PM
Export as bmp then use Serif PhotoPlus to convert to JPGOr install Draftsight as a freebie.

JAZZCNC
10-09-2012, 10:49 PM
Or install Draftsight as a freebie.

2 year ago that mate sure he'd have found something better by now.!