Limit Switch for Self Righting Lever

Hi Guy's,

I'm cobbling together my first robot and I would still be very much at square 1 if it wasn't for this forum. Thanks everyone!!

I planning to use a limit switch for my self righter. It's basically 2 levers 50cm long that sit horizontally. They will be powered by a scooter motor driving a live axle with the levers at each end of the axle shaft. When engaged it will travel 180 degrees to the other side and self right the robot. Then doing the oppsoite if needed by reverseing the motors polarity bringing the lever back to where it started. Hope that's clear.

From what I've read it looks like it may be possible to use a double throw double pole relay for this. What do you think?

Any thoughts on this would much appreciated.

Thanks
Ed

That'd be doable, as long as you wire it properly. How are your limit switches going to work, big diodes?

Thanks Rory,

Woking from this diagram. (I'll upload a pic when I get to a desktop) The RX is connected to a servo SW which is connected to the coil input of the relay. The Relay in closed position gives the motor no power. When activated via a the servo switch it switches on the battery power to the motor. To reverse the operaton there would be a second relay and servo SW coming from another channel on the RX wired in exactly way but with polarity reversed.

I have no exsperience with relays. Can you set a time the relay stays switched on before if returns to it's normally closed position?
Any examples of the kind of relay and servo SW I should be looking at would great.

Thanks

what type of scooter motor you planning to use Ed ?

Hi Mark. I was thinking of using a 24v 500w ebay scooter motor geared down.

Attachment 6813

Hi Guys,

Still trying to get some clarity on this.

Here's a pic of the circuit diagram I got the idea from. After further delving I'm thinking of wiring an RX Channel output to the coils of a Time delay relay (SPDT). When the given RX channel sends voltage to the the relay it will switch on for the amount of time set by the time delay and engage the motor (What ever it takes to move the levers 180 degrees) and self right the robot. To reverse the operation I will wire a second circuit from another RX channel and a second time delay relay but will have the motors polarity reversed so it swings the levers back to where they started. Will it work? :-|



Time Delay Relay - http://uk.farnell.com/amperite/120aa...vac/dp/1088945


Any thoughts and advise much appreciated?



Thanks
Ed

Why not just chuck in a brushed ESC + an arduino to enforce the limit switches? MUCH more robust than a whole bunch of relays in a combat robot, much more compact and gives you a greater amount of options on how to impose limits.

You also have a huge misunderstanding of the RX channels. They are not sending voltage, they are sending a digital signal (PWM). It is actually more off than on. You also cannot draw that much power from the signal line without likely blowing the RX. So you need something that takes the signal of the RX and switches an output. At this point a Brushed ESC really is simpler, likely cheaper and more robust.

EDIT: Just realised you have a servo switch inbetween for the RX->Sw conversion. You are vastly over complicating the system with very outdated components that do not fare well in a combat robot.

Other things, if you have a weapon use that for self righting, or if you're putting this in without a weapon just make it a lifter. A 500w scooty motor is a heavy thing to have only self righting in your robot. It's far more efficient on weight to combine it with your weapon.

Thanks Shakey,

So your saying it would better to approach this like a drive system? RX - ESC - MOTOR and program an arduino to impose the limits?

I would never have thought of that. I'll look into arduino programming.

I was thinking of turning this into some sort of weapon once it's up and running :)

Many Thanks
Ed

To be honest, if you're using a brushed motor, you can do without the arduino. If you add a linear actuator-style diode and limit switch circuit after the ESC but before the motor, it should just stop the arm from going further than it needs to. You can still use an arduino if you want, it depends where your skills lie as to which one you want to pick. If you want an example of the arduino method though (which I used with a brushless motor) you can check out my build thread (Aegis). I have a video talking about how it works too.

Thanks Rory,

Just been looking through your Aegis build diary. Great thread! Nice 1.

The limit switch diode option looks like a more appropiate solution to me. Just to make sure I'm getting what your saying heres an order of component connection.

1. RX

2. ESC

3. Limit Switchs (Placed near the axle under the levers)
Limit Switch - http://uk.farnell.com/itw-switches/1...ever/dp/521875


Wiring and diodes more or less like this. RX instead of reversing switch:

Attachment 6826


4. Motor

Cheers

Yes, that looks fine to me. I'm sure diodes must exist for the voltage and current rating you'll need in a Heavyweight.

This is a neater method that requires no diodes. Also allows the use of smaller limit switches as they don't carry the motor current.


Attachment 6827

I don't recognise that circuit symbol - the resistor with the dotted line and the switch. Is it a transistor of some kind, and F and R lead into the gates?

-Edit- Never mind, that doesn't make sense. I don't know what it is.

It's a relay :P the 'resistor' is the relay coil, and the dotted line shows which contacts the coil is connected to

Ohh of course! My bad, I'm used to the coil part looking more rounded.

Thanks Rory,

So no need for an ESC? connections from the RX would be:

RX ch a - servo sw - F forward - limit sw 1 - relay coil 1
RX ch b - servo sw - R reverse - limit sw 2 - relay coil 2 ?