Photocell Bonus

rocketchicka
Member
Member
Posts: 49
Joined: February 2nd, 2009, 2:09 pm
Division: C
State: MI
Has thanked: 0
Been thanked: 0

Re: Photocell Bonus

Post by rocketchicka »

can someone tell me how to set up a photocell? I tried setting them up with a motor, but nothing's happening. Do need batteries or something? :?:
2010 Events-State Results:

17th Mission Possible
7th Egg-O-Naut
32nd Technical Problem Solving
18th Remote Sensing
cypressfalls Robert
Exalted Member
Exalted Member
Posts: 499
Joined: January 6th, 2009, 7:54 pm
Division: Grad
State: TX
Has thanked: 0
Been thanked: 0
Contact:

Re: Photocell Bonus

Post by cypressfalls Robert »

rocketchicka wrote:can someone tell me how to set up a photocell? I tried setting them up with a motor, but nothing's happening. Do need batteries or something? :?:
p-----------------X----Battery----X------------|
p-----------------X------------------------------|Motor

p= photocell
X= joint
-= wire?
|= motor
bugsrcool
Member
Member
Posts: 14
Joined: February 12th, 2004, 6:49 pm
Division: C
Has thanked: 0
Been thanked: 0

Re: Photocell Bonus

Post by bugsrcool »

Use the setup on the first page under the Wiki. It works perfectly on some motors. Some motors have way too much current and too little resistance to work with a photocell. We tried several motors until we found a couple that worked well under the amount of photoresistors we put in and the light source. None of them worked at full power because there was always some resistance still left in the photocells even under some very bright lights.
...and the bugs shall rule the world!!!
Dark Sabre
Admin Emeritus
Admin Emeritus
Posts: 705
Joined: January 4th, 2004, 5:53 pm
Division: Grad
State: KY
Has thanked: 0
Been thanked: 0
Contact:

Re: Photocell Bonus

Post by Dark Sabre »

I updated both the fist post in this thread and the wiki diagrams to be more clear about what design should be used (remove all references to that random resistor), reworded some stuff that has been made irrelevant because of the rules clarifications, and hopefully made it more obvious that a battery was required in the circuit.
fleet130
Staff Emeritus
Staff Emeritus
Posts: 433
Joined: November 10th, 2001, 3:06 pm
Has thanked: 0
Been thanked: 0
Contact:

Re: Photocell Bonus

Post by fleet130 »

I was able to get the motor in this solar racer kit to spin with just the light from a common 2-cell mini-maglite.
ImageImage
[Click Photos to Enlarge]

These kits are pretty expensive (in my opinion), but it gives you some idea of the size of the motor. You could replace the photo-voltaic photocells with photo resistors connected in parallel and a battery as explained above. These tiny motors are often available from surplus liquidators. I have bought them from Radio Shack. They were being sold as replacement motors for the small re-chargeable radio-controlled cars.

Kits from Tamiya, such as the "Blue Eagle" and "Honda Dream", have motors that are about the same length and are about twice the diameter.
Image
[Click Photo to Enlarge]

As a much less expensive source you might try googleing for somthing like "surplus pager motor"
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!
Flavorflav
Member
Member
Posts: 1388
Joined: February 5th, 2006, 7:06 am
Division: Grad
State: NY
Has thanked: 0
Been thanked: 3 times

Re: Photocell Bonus

Post by Flavorflav »

fleet130 wrote:I was able to get the motor in this solar racer kit to spin with just the light from a common 2-cell mini-maglite.
Proving that solar cells could have worked. I don't know why they banned them - there is so little choice in this year's rules already.
Uncle Fester
Member
Member
Posts: 149
Joined: May 14th, 2001, 4:59 pm
Division: Grad
State: IN
Has thanked: 0
Been thanked: 0

Re: Photocell Bonus

Post by Uncle Fester »

I had two devices have working photocells at this past weekend's invitational. One was from my team, done the night before with one working test beforehand.

ELECTRONICS GOLDMINE sells a pack of tiny 3v cellphone vibrating motors for (I think) $2.50. We also got a dozen of the 75 cent photocells on sale. While we were at it, we got an assortment of gearhead motors; real powerful and nice and slow.

Photocells had a bright resistance of 24 ohms. This was low enough to be a problem! So, each photocell was wired in series with a 24 ohm resistor to bring the bright resistance UP to 50 ohms. This effectively increased the number of photocells needed to four, but it eliminated overheated photocells, which causes aggravating intermittent problems.

Hooked up to 9v (D cells-- we don't use those rectangular niners), there was plenty of voltage and power available to run the 3v cell pager motor, which hopped around on a precarious spot, fell about 50cm, reached the end of its wire, and tripped a really touchy snap switch.
Uncle Fester, Maker & Fiction Science Writer

The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
Flavorflav
Member
Member
Posts: 1388
Joined: February 5th, 2006, 7:06 am
Division: Grad
State: NY
Has thanked: 0
Been thanked: 3 times

Re: Photocell Bonus

Post by Flavorflav »

Uncle Fester wrote: Photocells had a bright resistance of 24 ohms. This was low enough to be a problem! So, each photocell was wired in series with a 24 ohm resistor to bring the bright resistance UP to 50 ohms. This effectively increased the number of photocells needed to four, but it eliminated overheated photocells, which causes aggravating intermittent problems.
Aha, that might explain some of the things we have been experiencing - the CDS cells seem inconsistent, which has been driving us nuts. I'll try the resistor.

BTW, what kind of light source are you using?
Balsa Man
Coach
Coach
Posts: 1318
Joined: November 13th, 2008, 3:01 am
Division: C
State: CO
Has thanked: 0
Been thanked: 3 times

Re: Photocell Bonus

Post by Balsa Man »

One combo that seems to be working nicely-

9.6v battery from a portable drill. 12v lamp Home depot- landscaping light, oh, 1/14" diameter; seriously bright w/ 9.6v battery; photoresistor about 1/4" in front of the lamp in a little box. Photoresistor to a Radio Shack 5v relay, relay to a 12v computer cooling fan. Fan reaction time to when the light is tripped is almost instantaneous, and plenty wind from the fan to push a paddle on the top of a lever (pivoted at the bottom); lever falls.....leads to the next action....
Len Joeris
Fort Collins, CO
Uncle Fester
Member
Member
Posts: 149
Joined: May 14th, 2001, 4:59 pm
Division: Grad
State: IN
Has thanked: 0
Been thanked: 0

Re: Photocell Bonus

Post by Uncle Fester »

Problem with the arrangement immediately above, the fan motor gets none of its electricity from/through the photocell(s). It gets it through a switch contact (relay).

Answer to the latest question addressed to me: the photocells were lit up by a $1.00 dollar-store 3-LED tap light, and the whole setup was enclosed in a bright shiny coffee can, with the lid sprayed with black spray-on "plasti-dip" that's used on tools and such for waterproofing. Kids chose that because itw as black and thick.
Uncle Fester, Maker & Fiction Science Writer

The Misadventures of the Electric Detention
The Revenge of the Electric Detention
The Curse of the Electric Detention
>> Three full-length adventures, 26 short stories and counting!
Locked

Return to “Mission Possible C”

Who is online

Users browsing this forum: No registered users and 3 guests