help controlling magnetic coil

[Xenosis]

help controlling magnetic coil [SOLVED]

Hi, new to forums but looks great so far.

I have a very old RC car I was planning to re-purpose that has a rear motor and front magnetic coil driven left/right steering.

I can control the motor no problem but can't seem to figure out or find a way for how to control the steering unit.

From what I understand, I need to somehow drive a current through it in either direction to change the north and south of the magnetic coil.

By changing the north and south of the coil electronically, it pushes the floating magnet left or right thus turning the wheels.

Any help would be appreciated. I don't have the specs for the original circuit and doubt they would be available.

The chip on this thing in case anyone is interested is a NIKKO 501B (2614L).

basic info:
runs of if 4 AAA's (4.5v)
normally would use 49MHz radio signal to control

mechanism:
**broken link removed** **broken link removed**

more:
**broken link removed** **broken link removed**

pcb circuit:
**broken link removed** **broken link removed** Red and black wires seen are supply lines from the 4.5v AAA stack. The thin copper wires were the coil leads. The #29 pins as seen in the top down view were the motor leads.

poorly drawn magnetic coil diagram:
**broken link removed**

 

[davenn]

hi Xenosis

welcome to the forums

I can sorta imagine the setup ... how about taking a couple of sharp and well lit pics of the mechanism, it may help us all to give some suggestions
Keep your images to below 800x600 and preferable compress them to less than 100kb

cheers
Dave

 

[Xenosis]

added photos to the original post showing the mechanism.

you can see the resting place and one of two of the triggered positions.

thanks for your reply

 

[4pyros]

Last time a saw something like that there was a 3rd connecting that broke off inside the coils. Are you shore it only had two connections?

 

[Xenosis]

I am pretty confident that there was only ever these 2 wires. They are effectively all the same single wire that makes up the coil itself.

 

[4pyros]

OK then you need an "H" bridge to drive the coil both ways. They use the same to revrse motors. You acn look it up.

 

[Xenosis]

Well I figured it was something like that so I tried applying a 5v usb supply to it thinking the current direction would create the different magnetic field but nothing happened.

The motor works however when doing this. I am familiar with H-bridges and have set up many.

So I thought maybe the coil just isn't drawing any current so I tried running the motor in series with the coil to see if it would trigger the coil in one direction but not even the motor worked in this configuration.

 

[4pyros]

I tried applying a 5v usb supply

A USB supply may not have enough current.
Can you try a 6 or 9 volt battery?

 

[alec_t]

Have you actually checked that the coil is intact, not open circuit?

 

[jpanhalt]

Is the little metal thing in the steering arm a magnet, magnetic, or just a cover piece?

If it is attracted to the coil (that is, magnetic) and is not a magnet, then reversing the polarity of the electromagnet won't help. I would tend to agree with 4pyros then that there is a third connection. It may just be a ground connection, like a center tap, so that each side of the electromagnet can be energized separately.

I agree that checking continuity of the two leads is a good next step. This may be obvious, but have you stripped the enamel insulation from the wire that you are trying to attach to?

John

 

[Xenosis]

Is the little metal thing in the steering arm a magnet, magnetic, or just a cover piece?

If it is attracted to the coil (that is, magnetic) and is not a magnet, then reversing the polarity of the electromagnet won't help. I would tend to agree with 4pyros then that there is a third connection. It may just be a ground connection, like a center tap, so that each side of the electromagnet can be energized separately.

I agree that checking continuity of the two leads is a good next step. This may be obvious, but have you stripped the enamel insulation from the wire that you are trying to attach to?

John

There is a magnet seen mounted in the steering arm. Also, in the coil there are the two (coil amplifier?) magnets. ie: the two pieces will attract each other and are effectively the north and south of the coil magnet. (check pictures above)

How can i check continuity? I am getting a resistance of 0 or just no reading with a multimeter.

The wire has no enamel insulation and appears to be bare wire.

Tthere is tape around the coil glued in the middle separating the two end leads. One side is taped and in contact with the center of the coil out to to edge while the other is not taped and just comes from the opposite edge.

I thought the same that perhaps the coil was or could be split into two separate on/off magnets. I will try energizing just one half and see what happens.

Uploaded a couple more pictures in the main post.

I tried using a 9v battery to no avail.

When using the 5v USB supply the first time it actually twitched a little but I wasn't able to repeat that.

 

[4pyros]

The wire has no enamel insulation and appears to be bare wire.

The wire must have an enamel insulation!! It is probably clear so you can't see it. Sand or scape or burn it off the ends and test again.

 

[alec_t]

I am getting a resistance of 0 or just no reading with a multimeter.

That's suspicious. Is your meter a digital one?

 

[jpanhalt]

Try soldering to the wire. If it is bare, the solder will stick easily and wet the surface. If it is insulated, even if it is insulation that can be soldered through, it will behave differently.

Zero and no reading are different. If you measure across a short piece of wire lead from a resistor, what do you see?

John

 

[Xenosis]

The wire must have an enamel insulation!! It is probably clear so you can't see it. Sand or scape or burn it off the ends and test again.

At closer examination of the original contact on the PCB, I can see that yes the copper color is in fact the enamel and the wire is a silver color underneath.

This is probably the problem (trying to pass current through effectively an insulation).

That's suspicious. Is your meter a digital one?

It is a digital one. The enamel situation would account for this.

Try soldering to the wire. If it is bare, the solder will stick easily and wet the surface. If it is insulated, even if it is insulation that can be soldered through, it will behave differently.

Zero and no reading are different. If you measure across a short piece of wire lead from a resistor, what do you see?

John

I get a reading of definitely zero reading across bare wire of a resistor so I was getting no reading across the enamel insulated wire (duh).

Going to find some sandpaper to scrape the enamel and test again.

Uploaded some more pictures to original post.

 

[4pyros]

The coil/coils would not work at all if the wire was uninsulated.
It must have enamel on it for it to work at all.
Other wise it is just one big short!

 

[Xenosis]

The coil/coils would not work at all if the wire was uninsulated.
It must have enamel on it for it to work at all.
Other wise it is just one big short!

Makes total sense.

After soldering most of the enamel off of the leads I am getting a reading of 29.2 Ohms.

Success!

Using still just the 5v USB supply I can actuate it in either the left or right direction by changing the voltage and ground leads.

Will be completely controllable by an H-Bridge.

Thanks for all your help.

 

[4pyros]

Glad to here you got it working! Have fun