Triode
Well-Known Member
As some of you might know, I'm a Mechanical Engineering student and I make my tuition by contracting custom equipment, mainly for professors, at first it was purely mechanical stuff, but as I've learned electronics it has become more robotic/mechatronic, and as that trend is increasing my job offers and the amount of pay offered, I'd like for it to continue.
I have been approached about making a force oscillating tester. Meaning based off of a function it is to apply a force, not a position. Desired features are that it can accept programmed functions, shut off after a desired time or number of cycles, and record the displacement and forces experienced at the end of the part being tested, in this case a bike fork.
specs:
applicable force: +200 to -200 lb
cycle speed: .25 to 3 cycles per second
max displacement: +/- 2 inches,
20 position and force samples per cycle
accurate to +/- .05" and +/- 2lb
Due Date September, 2010
Now here's the thing I would like to discuss. Just doing this project is no problem, I have already designed and built one major component, a pneumatic cylinder with position and force feedback and attached it to a PID device and microcontroller so that a 0-10v signal gives you -300 to 300 lbf, now I'm on to the control and data logging aspect. I have access to a full electronics lab and temporarily using equipment there I have been able to connect a function generator, a data logger and a USB daq device with digital output to make a setup that does what the professor has requested, and if I were lazy I could just get a catalog, order each of those components and be done with it. But the problem is that would be a bit wastefull, it would cost around $3000, most of the equipment would be using only a little of the capabilities that make it so expensive, and it wouldn't even be that user friendly; the user would need to set the timer in one place, set the function on another device, set up the DAQ device, and covert the data when they were done.
Now looking at how basic those specs are, am I the only one who thinks a microcontroller connected to a windows application in VB or C# could handle all of this? Were talking about +/-2lbs in a 400lb span, that's only 200 divisions, a 10bit ad gives you 1028, the same goes for the 4 inches divided into 40 positions. So the data logging is nothing big, and when I asked about the function generation he said it didn't need to be highly accurate and that "a sine wave approximated by 5 or 6 force levels would be suitable" (I think I can do better than that, the pneumatic servo I built does about 2000 different force levels). The function generation could be quite simple it seems to me, and I've worked with VBA, C#, C++ and VB plenty.
But still this seems awfully ambitious, so I'm not sure if I would be getting in over my head to try this. The upshot is, if I try and fail I wont have lost much, I can still default to just buying equipment, which is what I would have done anyway. And just think how wowed he would be if instead of a $3000 pile of equipment, I give him a box with a usb cable and a neat little windows app that sets your function, cycle count/run time and handles data logging, and sends it all to excel or access. It would be cheap too, $8 for a usb PIC, $12 for a DAC chip, $6 for some amps, round up for casing, power adapter, and all the little components and this thing should be under $100.
By the way, since some might question why I would spend my time on this, I'm getting payed well, my rep at the university gets me jobs, and I'm getting class credit for an independent research. He has set the budget high enough that I could just buy all that equipment, but that would not be an efficient, or elegant solution. This way seems really cool though, I'm just not sure though, it seems easy and hard, so give me your input, how would you do it? Why is it practical? Why is it impractical?
I have been approached about making a force oscillating tester. Meaning based off of a function it is to apply a force, not a position. Desired features are that it can accept programmed functions, shut off after a desired time or number of cycles, and record the displacement and forces experienced at the end of the part being tested, in this case a bike fork.
specs:
applicable force: +200 to -200 lb
cycle speed: .25 to 3 cycles per second
max displacement: +/- 2 inches,
20 position and force samples per cycle
accurate to +/- .05" and +/- 2lb
Due Date September, 2010
Now here's the thing I would like to discuss. Just doing this project is no problem, I have already designed and built one major component, a pneumatic cylinder with position and force feedback and attached it to a PID device and microcontroller so that a 0-10v signal gives you -300 to 300 lbf, now I'm on to the control and data logging aspect. I have access to a full electronics lab and temporarily using equipment there I have been able to connect a function generator, a data logger and a USB daq device with digital output to make a setup that does what the professor has requested, and if I were lazy I could just get a catalog, order each of those components and be done with it. But the problem is that would be a bit wastefull, it would cost around $3000, most of the equipment would be using only a little of the capabilities that make it so expensive, and it wouldn't even be that user friendly; the user would need to set the timer in one place, set the function on another device, set up the DAQ device, and covert the data when they were done.
Now looking at how basic those specs are, am I the only one who thinks a microcontroller connected to a windows application in VB or C# could handle all of this? Were talking about +/-2lbs in a 400lb span, that's only 200 divisions, a 10bit ad gives you 1028, the same goes for the 4 inches divided into 40 positions. So the data logging is nothing big, and when I asked about the function generation he said it didn't need to be highly accurate and that "a sine wave approximated by 5 or 6 force levels would be suitable" (I think I can do better than that, the pneumatic servo I built does about 2000 different force levels). The function generation could be quite simple it seems to me, and I've worked with VBA, C#, C++ and VB plenty.
But still this seems awfully ambitious, so I'm not sure if I would be getting in over my head to try this. The upshot is, if I try and fail I wont have lost much, I can still default to just buying equipment, which is what I would have done anyway. And just think how wowed he would be if instead of a $3000 pile of equipment, I give him a box with a usb cable and a neat little windows app that sets your function, cycle count/run time and handles data logging, and sends it all to excel or access. It would be cheap too, $8 for a usb PIC, $12 for a DAC chip, $6 for some amps, round up for casing, power adapter, and all the little components and this thing should be under $100.
By the way, since some might question why I would spend my time on this, I'm getting payed well, my rep at the university gets me jobs, and I'm getting class credit for an independent research. He has set the budget high enough that I could just buy all that equipment, but that would not be an efficient, or elegant solution. This way seems really cool though, I'm just not sure though, it seems easy and hard, so give me your input, how would you do it? Why is it practical? Why is it impractical?
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