Let's Make Robots!

My First Robot - Motor control for tracks

Hello all

So, I've been lurking this forum for a while now and finally decided to make my first robot.

I started out reading the "Start here" guide - and it's a really cool guide by the way :)

However I want to build a tracked robot and no wheels.
So I went to Technobots and found the RP5 Tracked Chassis.

I think this Chassis is really cool and all, but in the specs it says: 

* durable plastic body
* 6-AA battery holder included
* two brushed DC motors with 210 mA free run and 2.4 A stall current at 7.2 V
* maximum speed of 6 in/s (15 cm/s) at 7.2 V
* ability to scale inclines limited only by friction
* dimensions: 18 x 14 x 6 cm
* weight: 425 g 

My concern is marked with bold where it specifies "2.4 A stall current".
I went back to the "Start here" guide, to figure out if the motordriver L293D would be able to pull this off.
Apparently it can only deliver 1.4 A stall current...

Wont the L293D fry?

My question is: What do I do if I want to use the PICAXE starter kit with the RP5?


BTW: Technobots also has some really cheap solarbotics gearmotors :)At least from what I could find.
(Nothing to do with my post, just wanted to point it out)

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It might fry, so use an L298 instead.

Ah - duh.. Why didnt I think that :) There is always another chip!!

Well thanks for your reply.

 Edit: Will it fit into the PICAXE board? I cant seem to find a datasheet on it.

I don't think it will fit, from the pin outs I found it seems that you will have to find some other way to connect it to the Picaxe board.

There is one more solution to your problem;

in the L293D datasheet it suggest doubling it up, as in soldering a second one on top of the first one. This would make them able to handle the current I think and it would work even better if you added a heat sink.  

Hehe, a heatsink would be nifty :)

But if soldering two L293D together would be enough to deliver the current, what about the supply?
I guess I would have to double the supply voltage too.

Where did you find your datasheet?

Here is the data sheet, http://www.st.com/stonline/products/literature/ds/1773.pdf

Google image does give a few examples of it being used so that helps as well.

Don't see why you would need to double to supply, but this might depend on how you power it.

BTW how are you going to power the robot? Are you going to use 2 power sources like on the picaxe 28 board or make your own ?

Thanks for the datasheet.

I think I'll try to use the source on the picaxe 28 - I am able to make my own supply, but it would be easier to just pull on the picaxe 28.

I am not entirely sure how the picaxe 28 is designed, so I think I'll start out with buying the parts for the "start here" robot and then get some tracks later on.

My brother is studying Mechanical Engineering and when I told him I was building a robot he went ballistic :D

So I think I just got myself a very good partner - at least when it comes to bodyparts.

 EDIT: I just found this in tips :)