Relay circuit help

[Omega Ra]

Hey guys. a little background first. I am making a robot lawnmower based on a simple relay circuit. This is my first time making a circuit and it works, but not as I expected it to. The way I thought it was going to work was, robot goes forward, hits bumper which activates a switch to switch the relay, thus reversing polarity on motors causing it to reverse (does this) but I put bigger Caps on one relay thinking it would hold that relay open longer and thus the wheels would turn backward slightly longer than the other side, thus turning the robot when it backs up. However it only backs up, then sits there for a second then goes forward again. Here is a drawing of my schematic (sorry I am not good at it). With one alteration, I forgot to draw in the Resistors (0.25W 10 Ohm) before the first diode. toward the side I drew what the relay connections are a little bigger so it is easier to see. On one side/relay I have 2 220uf capacitors, and on the other I have 1- 220uf; 1 - 470uf and 1- 1000uf capacitors.

As I said it drives forward fine, when it hits it's bumper it does back up, but instead of turning, it backs up slightly, sits there for a second and then just goes straight again...any help would be greatly appreciated.

 

[aljamri]

Hi,

If you can redraw it again proparly and provide sort of numbering for refrence, this mekes it much easy for us to under stand and help you if possible.

 

[KeepItSimpleStupid]

You could rethink this a bit and use 2 relays:
1. Direction (Fwd/rev)
2. Not Enable

You might think about an impulse relay for direction.

Not sure how you might implement turning,

The other way is FWD relay and a REV RELAY

I don't know if you want to consider Dynamic Braking where the motor is shorted when stopped.

These are ideas, because I am hiving difficulty following your schematic.

 

[Omega Ra]

I will try to re-draw the schematic to make it clearer, plus I will include the original one where I got the idea in the first place. Hopefully between his and mine you will see what I mean.

 

[Omega Ra]

Okay new Schematic

Okay here is the new version, I altered the original to how I did it. Let me know if the quality is good enough to read

 

[alec_t]

1) If you want the mower to turn why are you delaying the drop-out of both relays?
2) By delaying the drop-out you are keeping the motors stalled while the mower is against the obstruction. They might overheat.
3) For a small relay (100Ω 50mH coil) the capacitor values you are using will give only about 120mS difference between the two drop-out times; hardly enough time to turn the mower at all.

Edit: BTW the drawing is only just readable with difficulty. What software are you using for it? (I'm an advocate of the LTSpice schematic capture function). JPG images should be avoided for schematics. GIF or PNG is much clearer.

 

[Omega Ra]

I just printed out the guys original circuit drawing, altered it and scanned it back in, sorry for the quality. As for the other parts, I am merely trying to replicate someone else's circuit, with in put from one other guy. What should i do to make it work? I have never taken any classes or anything, i am just learning as i go.

Edit: should I just remove the caps from one side?

EDIT2: actually, the motor does reverse and it does back up, it just doesn't turn...it backs up stops for a second, then drives forward again.

 

[ronv]

You need to make sure you have forward and reverse wired correctly to the motors. The circuit you have delays the turn off of the relays. One more than the other to make it turn, Make sure when the relays are on the motors are in reverse.

 

[alec_t]

Unless motor heating is already a problem you could try removing the 2 x 220u caps from the one side and adding them in parallel with the 3 caps on the other side. Also, remove the superfluous 2 diodes connected to the relay coils.

 

[Omega Ra]

okay, so take the caps off the one side and get rid of the diodes between the caps and relay?

 

[Omega Ra]

edit: nevermind I looked it up.

 

[Omega Ra]

Unless motor heating is already a problem you could try removing the 2 x 220u caps from the one side and adding them in parallel with the 3 caps on the other side. Also, remove the superfluous 2 diodes connected to the relay coils.

here's one thing though, if I remove the two caps from the one side, will the relay stay open long enough to even get it to back up at all??

 

[ronv]

The way you have it now it should back up a bit before it turns. If you take them out of one side it will just try to turn.

 

[Omega Ra]

it does back up now, so I should leave the the 2 220μf ones and just add more to the other side, was thinking of taking out the 220μf from the three and adding in another 1000μf, think that would be enough....so 2x 1000μf and 1 - 470μf...or should I add a second 470 as well?

 

[Omega Ra]

As of right now it backs up briefly, then pauses and goes forward again...any idea as to why it pauses?

 

[ronv]

There are 2 reasons:
- It takes a higher voltage to "pick" the relay than it takes to "hold" it.
- There is some time to charge the capacitors thru the 10 ohm resistor. this is probably quite a bit less than the time it takes for the relays to discharge them.

What is the coil resistance of your relays?

 

[Omega Ra]

good question. here is the blerb from the site I bought them from.

- Color: Yellow
- Material: Plastic + copper
- DIP type, 8-Pin
- 1A 125V AC
- 2A 30V DC
- High Switching capacity: 125VA/60W
- Coil power consumption: 0.15W
- With 2 group switch contact form
- Coil voltage: 12V
- Electrical life: 100,000 times
- Mechanical life: 10000,000 times
- It has low coil power consumption and highly sensitive.
- Contains 5 pieces per pack
- Great for DIY

 

[Omega Ra]

There are 2 reasons:
- It takes a higher voltage to "pick" the relay than it takes to "hold" it.
- There is some time to charge the capacitors thru the 10 ohm resistor. this is probably quite a bit less than the time it takes for the relays to discharge them.

What is the coil resistance of your relays?

I just put my tester across the coil of one of the relays and got .717 kΩ, I also tried taking out the 1000μf cap and put in another 470, and took out one of the 220's on the other side. same result... slight pause when it backs up then just goes forward agai

 

[Omega Ra]

anyone?