Author Topic: Looking for the right set of components  (Read 711 times)

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Offline Backup69Topic starter

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Looking for the right set of components
« on: July 19, 2010, 10:31:45 AM »
Hello,
 
This is my first newbie post, i hope i dont make a big fool of myself.
For a long time i have planned to assemble somekind of an robot, i have browsed your site and read tons of guides, and this is what i have come up with.
Be said that for starters i will only try programming and later on maybe get more creative.
This is my shopping list, please advise if something is totally wrong or missing.
Chassis: http://www.active-robots.com/products/platforms/stinger-details.shtml
Since it contains DC engines 7,5V 4A per unit i chose a driver http://www.active-robots.com/products/motorcon/sabertooth.shtml
For the engines draiver i have planned separate batteries 7,2V 5000mAh Ni-MH Powerpack or something like this.
Microcontroller will be Arduino MEGA. And this brings me to an question - if i supply the controller with 6V (4x GP AA Rechargeable Batteries 1300 NiMH with holder) then what will happen to all the sensors that require 5V supply? Would it require purchasing of 5 Volt switching voltage regulator or is the voltage going out from the controller reduced to 5V?
For starters i planned only 3 IR GP2D12 Distance Measuring Sensor and QTR-8A Reflectance Sensor Array for line follow function. The next step would probably be servos and possibly even a camera.
Since the engines included with my chassis already and have built in quadrature encoder featuring, then how does the feedback work - wires from engines or some other way?

ty

Offline Soeren

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Re: Looking for the right set of components
« Reply #1 on: July 19, 2010, 05:42:33 PM »
Hi,

[...] question - if i supply the controller with 6V (4x GP AA Rechargeable Batteries 1300 NiMH with holder) then what will happen to all the sensors that require 5V supply?
The Arduino Mega contains voltage regulation on board, so you feed the sensors from this regulated voltage as well.

6V is a bit low, as the regulator has a maximum drop out voltage of 1.35V @ 800mA (1.25V @ 500mA), so the input must be at least 6.35V at all times, assuming the max. current is used.
Further, 5 NiMH cells (6.0V nominal) will have a voltage of up to 7.25V when freshly charged, but only 5.0V to 5.5V when at the end of its discharge cycle, so with 5 cells, you'll never get the full discharge out of the cells.

Better feed it from the same battery as the motors (the 7.2V), then you'll only have one set of cells (and hence less weight) to worry about and if you get problems with noise from the motors, just filter it (ask here if you need help at that time).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Backup69Topic starter

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Re: Looking for the right set of components
« Reply #2 on: July 20, 2010, 12:44:12 AM »
Hello
the regulator has a maximum drop out voltage of 1.35V @ 800mA (1.25V @ 500mA)

Thank you for your thorough response. I have questions again: If i understand right then this big voltage drop happens because of load not only in the regulator?

ty

Offline Soeren

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Re: Looking for the right set of components
« Reply #3 on: July 20, 2010, 08:28:24 AM »
Hi,

If i understand right then this big voltage drop happens because of load not only in the regulator?
A voltage drop is inherent in all regulators. Low Drop Out (LDO) regulators like the one in the Arduino Mega (AM) is lower than the non-LDOs (which can be as much as 3.5V), but with LDOs, the bigger the better and the one in the AM is rather small. I have some big-ass types (7.5A nom.) that would exhibit a drop of around 0.12V at the same 800mA, but they are physically much much larger.

When you increase the current in a given LDO, the drop out voltage will rise too and vv. down to a minimum drop that the datasheet for a given regulator will reveal.

I'm not sure what you mean by "load not only in the regulator"?
The regulator doesn't care of loads it don't see.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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