Robot troubles.

I am trying to build a mini-sumo edgebot, as featured in Junkbots, Bugbots and Bots on Wheels. Below is a quick scan of the schematic I'm following. It is supposed to drive forwards until the edge sensor closes, at which point it will reverse and turn before carrying on.

Trouble is, it doesn't work.

The symptoms:

I have breadboarded the circuit, and when I connect the battery, it runs. But when I make the connection to simulate the edge sensor, both motors kick into reverse, but only for a fraction of a second, and then never again - further touches of the edge sensor elicit no reaction at all.

When I disconnect the battery, and trip the sensor, the LEDs light and the relays click, showing that the capacitor is still charged.

The only things in the breadboard not to "spec" are the motors - I haven't bought my intended motors yet, so I am trialling with a pair of un-geared 3V motors (these are the motors I intend to buy: http://www.ebay.co.uk item number 5855781458 )

How can I fix it so that it will react to the edge more than once in a combat?

Picture of Robot troubles.
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Gerrles6 years ago
wat type of relay u used and does this use a controller or does it runs by itself
Kiteman (author)  Gerrles6 years ago
(Woah, flashback!)

They are 5V DPDT relays, and there is no controller - this is a BEAM project.
NachoMahma10 years ago
. Oh. I just noticed that, according to Figure 12-3, the relay on the right is not getting full voltage to the coil - it's dropped through the LEDs. Probably doesn't affect anything, but I'd disconnect the right leg of the LED string, jumper from the left coil lead of the left relay to the right coil lead of the right relay and attach the LED leg to the right coil lead of the left relay. . And why two relays? One will do the job, since the motors aren't independent.
Kiteman (author)  NachoMahma10 years ago
The voltage-drop is supped to make the robot turn in reverse, so that it then drives away from the edge next time it drives forwards.
The only way to do that would be if the LEDs were in the power to the motor, not the coil. As shown, both motors get full voltage.
Kiteman (author)  NachoMahma10 years ago
But one coil switches off before the other, so the last part of the reverse only has one motor running.
. Hmmmmmmmmm. I can't imagine it making that much difference in pickup or dropout time, but I'm no engineer. Makes sense if it works and explains why two relays. . If I were gonna do something like that, I'd put the voltage drop in line with one motor's power during reverse, but, once again, I'm no engineer. . I'd also wire up the relay contacts different (power to C), but that's just me and would have no effect on operation.
i think NachoMahma is right. you only need one relay, because you are only using one switch.  Btw, the also need to be connected in the middle (where they both touch, right above the negative of the coil.) also, if you want the revers to last longer, you can use an NPN transistor, with a cap and resistor to control how long the base of the transistor if getting power, aka relay is engaged.
royalestel10 years ago
Are you reading my suggestions? I may be an electronics noob, but I'm a systems troubleshooting pro, and I can tell you that simplifying your circuit WILL help you narrow down what your problem is.
Kiteman (author)  royalestel10 years ago
OK, then, TroubleShooterPro, exactly how should I simplify my circuit?

What should I remove, and how do I compensate for its removal?
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