« Last post by knossos on February 27, 2014, 10:39:38 AM »
I dug out my version of the excel photoresistor calculator worksheet. It's a modified version of admin's spreadsheet from the tutorial you linked. I filled in your 5 Volts as the Vin and your values for Max and Min. It shows that even an 18 kOhm or 56 kOhm resistor would still give you at least 95% of the range a 33 kOhm resistor.
I attached the spreadsheet if you're interested and a (not so brief) explanation of it below. It was a quick rough up I did for my own use so it's nothing fancy, but gives a little bit more information for resistor selection.
The first three columns show what series the resistor is part of (E6,E12, or E24). Column D is the choices for resistor values. Column E is the most important column. It shows the output voltage range (Vmax-Vmin). The higher the range, the more sensitive your sensor. At the top of the column is the maximum range available with the resistors listed. Looking down the Range column, you will see red, yellow, and green entries. Green is the IDEAL choice (i.e. max range capable using resistors on the list). Yellow are GOOD choices (i.e. at least 99% of the max range). Lastly red are OK choices (i.e. they only give you 95% of the max range). You can adjust the scales at the top of the page to your needs. The next two columns are the max and min voltages if you configure the resistor as a pull up (so voltage decreases with light) and the last two columns are the max and min values if you use the resistor as a pull down (voltage increasing with light).
« Last post by knossos on February 27, 2014, 08:27:11 AM »
Photoresistors come in a wide variety of resistance values, so I would definitely go with the values you measured. Dark values can be as high as several megaohms and bright values can be as low as a few hundred ohms. Using your values (which seem accurate) the closest E6, E12, or E24 series resistor would be 33 kOhms (for 20, 10, and 5% tolerances, respectively). You could also use a 30 kOhm E24, or if you felt you needed a more accurate resistor, an E48 (2%) series or better would give you a 31.6 kOhm resistor. You really don't need the tighter tolerances though. If you don't have a 33 kOhm resistor you could just as easily go with the next higher or lower value resistor at the cost of some decreased sensitivity.
« Last post by kevinthesun on February 27, 2014, 12:23:39 AM »
Less then 10 N*m. I'd like to build a completely closed-loop control system to achieve more accurate torque value.
First I would like to start off by saying that I am not a mechanical engineer. I do not know anything about robots other than Robocop and the Terminator.
Why I'm here... I have an idea for a business that my partner and I are thinking about starting up.
How would I go about getting in contact with expert builders here? Mechanical engineering and robot automation is what we are aiming for.
If you are interested in talking about this, please contact me by Gmail at SuperMoverBros (dont know if im allowed to put email addresses on this post)
I would really like to meet someone in Los Angeles so that we might be able to talk in person. But that is definitely not a requirement.
« Last post by garriwilson on February 26, 2014, 08:20:06 PM »
I measured the resistance of my photoresistors under the couch (~200 kOhms) and under a lamp (~5 kOhms). The problem is, these are orders of magnitude different from what admin got here: http://www.societyofrobots.com/schematics_photoresistor.shtml
I understand that I picked two extremes (darkness under couch and right under a lamp), but how can my values be this different? Plus now if I calculate the resistor I need from R = sqrt(R_dark*R_bright) ~ 31.6 kOhms.
My question is should I go with my values, which seem a little outrageous, or stick with an R=1.5 kOhms like admin used in the tutorial?
« Last post by sdk32285 on February 26, 2014, 05:48:51 PM »
What is the torque range you need to sense?
Can you sense the current to estimate torque, instead of directly sensing the torque?
(It is easier and cheaper to measure current then torque)
« Last post by kevinthesun on February 26, 2014, 02:13:37 AM »
Does any one know tiny size torque sensor for electric motor shaft?
« Last post by Sylvestre on February 25, 2014, 10:49:32 PM »
I think "Aircraft Grade" is typically 7050 or 7075, but at this level, who's counting? :-)
Lol My mistake. Google is quite misleading. When you search 'aircraft grade' aluminum, 6061 is the first link.
« Last post by sdk32285 on February 25, 2014, 08:12:14 PM »
FWIW: If you want to do research in the end, it's probably a really good idea to spend your Master's time learning how the real world works, getting as much math, and hands-on application as possible. If you then go on to a PhD, you can use that practical experience and knowledge of the world to guide your research.
I completely agree with you from a practical perspective, however when you are applying to PhD programs they want to see prior research and publications. If you do not get that done as a masters student it can be difficult to accomplish. Ideally you should get research experience and practical experience.
« Last post by Webbot on February 25, 2014, 01:13:42 PM »
Ok - got your PM and indeed you do need to have even parity. To do this is a larger job then you may believe! Partly because if I'm going to allow the parity to be set then I should also allow stop bits etc to be configured.
This is fine for raw UARTs.
The complexity comes in Project Designer when using a device that uses a UART. eg the Blackfin camera, GPS etc etc all allow you to change the uart number being used - but, unlike the raw UART, should not allow parity etc to be changed as this is part of the protocol for the device. So I'll have to change every device that uses a UART to say whether parity/stopbits can be changed and make sure they are backward compatible with old projects where the user never expressed a preference (ie default to parity=none, stop=1).
This will therefore mean a new release of everything: board designer, project designer, webbotlib, and then all repeated for Studio variants....
So it aint gonna be quick! But I guess I should bite the bullet now.