harsh environment problem

copacetic353

im in the design/brainstorm phase for my robot and ive come across a mildly unique situation.

basically what i am going to be doing is taking this remotely controlled car:

http://www.rc10.com/ae/t3/kitt3.htm

im going to give this robot the capability to navigate through its environment precisely and move to waypoints as intructed.

i am also going to be sealing all of the electronics inside a "hull" as this is designed to be an outdoors robot.

now to the problem---->

being that i live in michigan, the ambient temperatures here regularly drop below the normal operating temperatures posted for the prop chip and prop control board.

ideas on ways to get around this?

dandreae

What is the temperature range that you are dealing with?

Regards,

Dave





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Dave Andreae

Parallax Tech Support·

RobotWorkshop

To start I would probably put the electronics in a sealed box much like they use for RC boats to keep out the moisture. Perhaps someone else can comment on the temperature range but you might be ok if you just insulate the box. Depends on how long it will be outside and what the temperate will end up being. In the extreme cold I would probably be more concerned with the battery pack to see how that holds up in the low temp. If you have new batteries then you might be ok but I know the Michigan winters will kill any questionable batteries and that is usually when we have to replace the one in the car.

Robert

dandreae

The temperature range for the Propeller chip is:

Ambient temperature under bias -55 °C to +125 °C

Storage temperature -65 °C to +150 °C



Regards,



Dave




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Dave Andreae

Parallax Tech Support·

Mike Green

The Propeller chip itself is rated for operation from -55C to +125C, well beyond what you will find in Michigan.

The Propeller (and more importantly the other devices around it like voltage regulators) generates heat.
It wouldn't take a lot of insulation to take the bite out of the cold using this heat.

I suspect you will have much more of a difficulty with the cold affecting batteries, drive motors, and servos
than the Propeller and its control board. If you're using the GPS receiver, that will be much more sensitive
to ambient temperature than the Propeller. Its operating temperature range is -40C to +85C, but I suspect
that its performance will tend to deteriorate towards the margins of that range. A little styrofoam insulation
would go a long way towards helping that.

RobotWorkshop

It usually doesn't get THAT cold here in Michigan. He should be all set in regards to temperature for the electronics.

Robert

Bruce Bates

Folks -

As far as batteries are concerned, if you don't mind spending a few bucks on batteries, take a look at the Ultra-Life (may be one word) batteries. As I remember even Radio Shack has them, or at least they did last time I visited the Ultra-Life web site. Google for both "Ultra-Life" and "Ultralife" and I'm sure you'll find their web site.

Regards,

Bruce Bates

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When all else fails, try inserting a new battery.

Beau Schwabe

LiFePO4 batteries have an operating range from -20 Deg C to +75 Deg C

Reference:
http://www.yesa.com.cn/pages.asp?id=3


Another battery option might be Li-Poly wich are rated from -10 Deg C to +80 Deg C

Reference:
http://www.all-battery.com/browseproducts/3.7-volt---2100mAh-15C-Li-Poly-Cell.html


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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 11/25/2008 4:42:22 PM GMT

erco

Amusing sidenote: Speaking of a harsh environment for a robot, CES 2008 had a featured presentation by Tandy Trower himself of Microsoft, showing MSRS running on a wireless connection to a robot onstage. Obviously there was a sizeable crowd watching, and you can imagine the resulting interference from cell phones, headsets, cameras, hifi, wifi, bluetooth, blackfin, IR, flourescents, gamma rays, you name it. The presentation didn't get far before the robot locked up. Tandy was unflappable and gave a great presentation nonetheless. I spoke with him afterwards (a terrific guy) and it was nice to hear his take on how difficult a live robotics demonstration is. The big boys have many of the same problems we do!

At Robodevelopment in Santa Clara last week, a Microsoft rep told me over lunch that they plan to have a simple tethered connection for the upcoming CES demos. As Dirty Harry said, "A man (robot) has to know his limitations."

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·"If you build it, they will come."

copacetic353

oh thats good about the propeller and prop board, i must have seen a different temperature rating. in michigan it can get very cold, if i remember there was a day here last winter where it was -10F with a wind chill of -25F BRRR. I want to design for temperatures like that, wouldnt hurt if i can get it done. prepare for anything [noparse]:)[/noparse].

mike green said that some of the components on the prop control board generate heat, any idea how much? my design now has all of the electronics inside a waterproof enclosure to keep out moisture. i was thinking about trying to incorporating some sort of controlled heating element but if you say that the prop control board generates heat, depending on how much, i might be able to avoid that all together. all parts except for the drive motor and maybe the steering servo will be exposed to the outside world.

thanks for the information so far, keep it coming!

Post Edited (copacetic353) : 11/25/2008 6:29:02 PM GMT

Mike Green

This is where a little knowledge and some common sense help. Usually logic circuitry requires a regulated power supply. Guess what happens with the energy that isn't directly used by the logic? That's right! It gets turned into heat by the voltage regulator. The more current drawn from the voltage regulator and the more voltage has to be dissipated, the more heat is produced, particularly with linear regulators (the most common kind). If you use a switching regulator, it draws power intermittently rather than continuously, thus reducing how much has to be turned into heat. That's why most linear regulators have heat sinks.

Logic circuits waste part of their energy input because on/off switching isn't ideal and some of that gets turned into heat. The faster the logic switches and the more of the logic that switches, the more heat is produced. Have a look at the heatsink in your PC attached to the CPU chip. The Propeller is a much smaller chip and runs slower, therefore produces less heat.

Basically, look at the power supply current draw of different parts of your controller. Most of that will get turned into heat. The exception will be the power that goes to the motors and servos. Some of that will get turned into heat as well, but at the motor.