Robot Schematic

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besupreme

New Member
Just thad a quick look at it.
Change the value of R2 to avoid little pieces of green plastic flying around ;)
I would add 150 Ohm to the SERTXD line.
Your servos will need a lot 5V decoupling capacity as they could draw a lot of power.
Your 7805 (if that is the regulator) will be HOT because it feeds servo power, too.
Think about a 5V switching regulator, that will build a lot smaller than the heat sink you probably need now.
If you want to build small and you have to isolate, think about optocouplers instead of relays.
Pulling down a port pin down to 0V may decrease battery life.
 
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geoff07

Senior Member
Nothing difficult then, just a Mars rover!

Some info about what you want it to do would help, and where you think there might be weaknesses. Personally, I would add an led that you can control by program. Very useful when debugging.
 
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Mattc141

New Member
@ BeSupreme:

I don't understand... R2 is part of the programming circuit and is 10K in the manual...

As far as servos go, I will probably run them off a separate supply - i.e. 4x AA Batteries. That will reduce the regulator heat output.

I will look into the regulators as switching may be more effective.

@geoff07:

It is a Rover Prototype probably the same as the one featured here: http://beatty-robotics.com/spirit-ii-mars-rover

My concerns are just in the practicality as I am not the most experienced and things are differen't on paper than practically.

Thanks for the Replies.
 
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besupreme

New Member
sorry my eyes - i meant R4 for the 12V LED ;)

Just see the link - now it looks a tiny little less autonomous than I thought.
 
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russbow

Senior Member
Congratulations on a superb presentation.

My only comment is the lack of current protection on each if the IN pins. The manual suggests 10K pull downs, which you have, and 1K series between the 10k and pin.

Maybe a lack of electrolytics around your motor driver chips could cause problems as well.
 
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inglewoodpete

Senior Member
No one has mentioned that the reset switch, battery and associated wiring will get awful hot if you press the reset. The switch is on the wrong side of R1.

Is the power connection the same type of plug/jack as the programming connection? Both drawings appear to be different versions of the same thing. Best to use different types.
 
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besupreme

New Member
Well don't ALWAYS trust old men with bad eyes. And LED heads NOT missing them didn't make it better ;)

Nevertheless, I tried again reading your schematic.

Consider using SB520 diodes or similar for D1 and D4. 1N4148 is only good for 100mA, and Shottkies reduce losses.

And maybe 3 470uF capacitors. 2 for the 12V supply of the L293D motor drivers and one for the servo supply. If you pwm the motors (I think you have to, unless your motors are very small), consider using low esr types like the ones in switching power supplies. PWM and motors can add a lot of current spikes.
 
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Mattc141

New Member
Thanks for all the replies.

@pete:
Changed the Switch to the other side of R1 and about the connectors - The power comes through a DC Barrel Jack Connector whereas the Programming Jack is the actual Picaxe Programming Jack just is a custom library part.

@besupreme:
Changed the diodes as reccommended as the PSU will exceed 100mA. Those look like a good choice from the data sheet.
Also added the Decoupling Caps for the 12V & 6V Supplys.
The motors are very small and therefore will probably not require PWM control. Quick Question - Why only 2x 470uF Caps on the 12v Supply for the L293Ds when there are 3 of them?

View attachment Rover Control Board Rev.C.pdf

Thanks Anyway,

Matt
 
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