Anyone Use Power Saver Features?

[cjwillms]

Has anyone ever tried to add power saver features to a robot? From what I understand, some motors (I'm mainly thinking about Servo Motors) tend to continue to draw power, even when they are not in use. So, why not just use a transistor or MOSFET, controlled by a microcontroller, to turn off the motor when not in use? It would decrease the reaction time of your bot, but it could greatly increase its battery life.

The same thing could be done for almost any part of the robot. For example, if it's moving forward, do you really have to have the collision sensors in the back of the bot on?

I seems simple to me, but I've never really heard much about it.

[Admin]

I think the reason it isnt common is A, most robots require everything to be on when they are used, and B, it just adds another level of complication to an already difficult task of building a robot . . .

Most often there are nearby power sources readily available so no need to save power.

Ive built like 20-30 robots and not one could afford to turn off a motor or sensor. I was once going to make one that went to self charge when its battery ran low, hence requiring me to turn off all non-essential stuff . . . but then I never got around to it . . .

But look into space robotics, like the mars rovers, they work off of solar cells so they require what you speak of . . .

If you are considering doing this, keep me updated, I am interested in stealing your ideas =P

[cjwillms]

I will probably do it my self. I think I will post the design for my robots legs latter today. I just wish I could actually start on it sooner ;(

[cjwillms]

I did a bit more research into the subject, and I think I found another way to save power. This time, it mainly has to do with a variable voltage regulator. I found this article, which basically shows you how to use them. It should be possible to use another MOSFET, controlled by a microcontroller, to switch between say 6v and 3v.

This can be useful if you just want your bot to mover slower, so you don't waist as much energy. Unfortunately, I have no idea how much power this can actually save since voltage regulators aren't 100% efficient, the motor efficiency is usually based on a curve, and the microcontroller will have to draw a bit more power to supply the 5v to the MOSFET.

Another disadvantage has to do with the added complexity of the circuit. Plus, you'll have to program your microcontroller to deal with the motor at those different speeds, which can almost double the size of your code, as well as use up a extra port on it.

Anyway, this coupled with the full on/off switch will give you a good bit of flexibility, but your looking at 3 ports (on/off, high v/low v, and signal to servo) just for one motor.

[Admin]

I recommend just not doing the power saving right now till you get the rest of the bot done. Keep your steps small.

You can always upgrade later 

[cjwillms]

I'm just trying to think up a few thing to add later on. I'll probably just continue to use the breadboad until I've actually finished the legs, as well as added the ir sensors.

BTW, what AutoCAD program do you use? I'll probably try to make some better designs for me to follow. I can use 3DSMax, which will work fairly good for this, but its a pain to get the mesurments right.

[Admin]

I use AutoCAD 3D Inventor.

[2Hektik]

Inventor is GREAT for prototyping...

If you're looking for some good open (free) programs for your projects try www.sourceforge.net and www.freshmeat.net, the also have good packages like SciLab for system modelling. Best of all they are free and you are free to change the program however you see fit...

[cjwillms]

I tired FreeCAD from Source Forge, but I didn't like it. I decided to use 3DSMax for my modeling.

[dunk]

i have a remote controll bot that you controll via a web brouser.
the idea being people at work can drive round my office, generally crash into things, display rude messages on the LCD, while viewing the environment from an onboard webcam.
during periods of inactivity i wanted as many systems to power down as possible as the bot often gets abandoned away from it's charger.

the main battery pack runs at 12v (10 x NiMh AA cells). any devices using the full 12v (on this particular bot, only the camera and transmitter) would power down after a set period of inactivity. mosfets are perfect for this.

for the lower voltages onboard, make sure you are using a switching regulator. these drop the voltage by switching the supply on and off, then smoothing out the output rather than the far more wastefull linear regulators that convert the excess power into heat.

for any 5v systems i wanted to power down i used the enable pin on a separate voltage regulator, cutting the power at source. (can't remember the regulator i am using at the moment. it's a 6 pin chip and needs an inductor and capacitor to function. it draws virtually no current when the enable pin is high. to switch it on you send the enable pin low.)
i switch off power to the servos as well. servos burn a lot of power even when not moving. the disadvantage to powering them down is that they no longer "hold" position.

the only systems that are left on during this low power state are the radio receiver and a pic micro to detect an incoming signal so it can switch on and off of the various devices.
the bot happily survives about 2 days away from it's charger on 10 x NiMh AA cells.

dunk.

[2Hektik]

Hey,
do you have any docs on said bot?

[dunk]

i'm afraid not.
documenting it has been on my "to do list" for quite some time but building my next bot always seems to get priority....
if/when i get round to it i'll post a link here.

digging through some pictures all i can find is a horrible low res one on my phone:
http://213.79.39.20/lmbot/lmbot.jpg
it was taken before i added the power charging docking thing to the front.

you can see the camera on it's pan/tilt servos at the top.
the camera uses a separate video transmitter. one of these in fact:
http://www.maplin.co.uk/Module.aspx?ModuleNo=27680&criteria=video%20transmitter&doy=22m4
the receiver is connected to the controlling PCs TV card.

control of the bot is via a pair of these:
http://www.lprs.co.uk/main/product.info.php?productid=154
one connected to a pic micro on the bot and the other connected (via a max232 driver chip) to a PC serial port.
the PC is running the web server that has the controll interface. when a button is clicked a string of controll characters is sent to the bot. the bot replies with flow controll info as well as any requested information such as battery voltage or temperature.

i'm using microchip PICs as the onboard controllers. i designed everything in a modular fashion. 1 pic handles the serial communication with the PC and issues instructions to the other pics via an i2c bus. (possibly a little over complicated but i wanted an i2c experiment any way.)

i'm using modified servos as drive motors. 1 more servo for steering and 2 mini servos to pan and tilt the camera.
the 3 wheel design allows for an impressive turning circle.

it was a great learning experience and my first real robotics project.
overall i'm pleased with how well it works.
the main draw back is the slight time delay induced by an internet controlled device. when people click a button it is typically 2 or 3 seconds before they see the image start to move.
my next robot project will try to solve some of these usability issues.


dunk.

[2Hektik]

Wicked, that looks and sounds pretty impressive for a first project! I've been meaning to start my own*serious* project for some time...Its just that I have to put uni first - and since I always put uni off until the last moment... Yeh, u get the picture