Thread: idea for linear belt drive
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!!:naughty:
thanks again Tom
20-01-2010 #12my 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
I think that once you get to 8'x4' belts arnt a cheap option, just cheaper than ball screws
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.
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.
20-01-2010 #14However open-ended belting is only available in 100m rolls, so this might not be as cheap as you might think!
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).
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
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.
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.
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