« Last post by waltr on February 28, 2014, 09:25:44 AM »
Aluminum is not that expensive and can be found at lots of places which is reasons it is a good material to use.
Scrap yards can be a good place to get aluminum cheaply, Home Depot, hardware stores and other consumer places can have aluminum but it is hit ot miss for them having what you need.
Also look into old computer stuff, floppy & cd drives tend to use thin aluminum chassis and can provide good pieces to use on a Bot.
McMaster-Carr has a good selection of aluminum so check their online catalog if you need a specific size.
« Last post by ignatius_gim on February 28, 2014, 07:48:24 AM »
Thanks for all of your answers. How expensive is aluminum and do you suggest going to a scrap metal yard or a mill, what about consumer stores like Home Depot? Also, could you just connect the motor righ tot the gear box and will it stay? Any other mounting options and where could you buy gear boxes? Thanks a lot.
« Last post by APJ1234 on February 28, 2014, 06:26:50 AM »
Hey Admin I have try everything but still my building of codes in VAR studio is not starting.
« Last post by garriwilson on February 27, 2014, 06:02:00 PM »
Thanks for the file, it was pretty useful for understanding and similar to the one admin had on the tutorial. I know you said photoresistor values can vary, but I did buy the exact same ones as in the tutorial, and the values are off by a lot. Admin had something like R_bright = 500 ohms and R_dark = 3300 ohms. My values are in kOhms, so that's a little concerning. I just want to make sure I didn't make some freak mistake before I go wire four 5kOhm resistors together and it ends up being a waste, you know?
Also, how much of a range do I really need? In the tutorial, the max Voltage Range that admin got with his 1.5 kOhm resistor was about 2 Volts. In my case I can get a 2 volt range with a 3.6 kOhm resistor. Are these two cases analogous? I mean, will the sensitivity of the robot to light be the same as in the tutorial, since my voltage dividers will produce the same max voltage range of 2V? Or since I have different values, will I need a wider range?
« Last post by strat321 on February 27, 2014, 11:24:58 AM »
So if in theory I would need even parity in the next month. .. I should look elsewhere? Raspberry pi etc.?
« 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?