Robot Hack Question

Google Groups
1

Hi,

Inspired by the Robot Hackday, #2 son and I have been taking an old baby
toy apart. We got down to the motor and found it has a component soldered
across the terminals. There is a pic of it here:

http://www.wuala.com/goopot2/public/motor-thing/

The component has “104” printed on the back. Could anyone explain what it
is and what’s it for please?

Thanks for the inspiration!

Dave.

2

Hi Dave,

It’s either a capacitor or a suppressor, either way, it’s just there to
reduce some of the electromagnetic interference that the motor would
otherwise produce.

JimOn 7 December 2011 14:44, Dave Potts dave@goopot.co.uk wrote:

Hi,

Inspired by the Robot Hackday, #2 son and I have been taking an old baby
toy apart. We got down to the motor and found it has a component soldered
across the terminals. There is a pic of it here:

http://www.wuala.com/goopot2/public/motor-thing/

The component has “104” printed on the back. Could anyone explain what it
is and what’s it for please?

Thanks for the inspiration!

Dave.

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3

From the description it sounds like a ceramic capacitor with a 100nF value. As Jim already said if it is across the motor terminals it is used for suppression of motor spark noise and will stop radios being interfered with. Quite often there are two more capacitors built in to the motor supply wires to make up a PI filter.

You could remove it if you wanted to. It shouldn’t affect the operation of the toy. If you do remove it the motor might cause snow on you tv or interfere with a portable radio when the motor is on

Regards

Alex

----- Reply message -----From: “Jim MacArthur” jim@mode7.co.uk
To: hacman@googlegroups.com
Subject: [HACMan] Robot Hack Question
Date: Wed, Dec 7, 2011 2:50 pm
Hi Dave,
It’s either a capacitor or a suppressor, either way, it’s just there to reduce some of the electromagnetic interference that the motor would otherwise produce.
Jim

4

Thanks for the info. I can see a good experiment here: put it near the tv
with and without the capacitor and see the difference. Is there a simple
(6 year old) explanation of why it works?

Dave.On Dec 7, 2011 3:46 PM, “Alexander Lang” alexanderlang1980@googlemail.com wrote:

From the description it sounds like a ceramic capacitor with a 100nF
value. As Jim already said if it is across the motor terminals it is used
for suppression of motor spark noise and will stop radios being interfered
with. Quite often there are two more capacitors built in to the motor
supply wires to make up a PI filter.

You could remove it if you wanted to. It shouldn’t affect the operation of
the toy. If you do remove it the motor might cause snow on you tv or
interfere with a portable radio when the motor is on

Regards

Alex

Sent from my HTC

----- Reply message -----
From: “Jim MacArthur” jim@mode7.co.uk
To: hacman@googlegroups.com
Subject: [HACMan] Robot Hack Question
Date: Wed, Dec 7, 2011 2:50 pm

Hi Dave,

It’s either a capacitor or a suppressor, either way, it’s just there to
reduce some of the electromagnetic interference that the motor would
otherwise produce.

Jim

On 7 December 2011 14:44, Dave Potts dave@goopot.co.uk wrote:

Hi,

Inspired by the Robot Hackday, #2 son and I have been taking an old baby
toy apart. We got down to the motor and found it has a component soldered
across the terminals. There is a pic of it here:

http://www.wuala.com/goopot2/public/motor-thing/

The component has “104” printed on the back. Could anyone explain what it
is and what’s it for please?

Thanks for the inspiration!

Dave.

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"HAC:Manchester" group.
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hacman+unsubscribe@googlegroups.com.
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5

A better experiment would be to get an AM radio, tune it to an unused frequency ‘not hearing anything except static’ and the turn the toy on. You should hear clicks, pops and hiss caused by the toy. This noise should be worse without the capacitor. I can’t promise you will see snow on the TV. It depends on your particular model of TV and its internal electronic circuitry. Digital TV receivers are less susceptible to RF interference.

To explain what is going on. Motors are essentially an electromagnet ‘rotor’ inside a coil of wire formed around a tube ‘stator’. As electric current is passed through the coil this creates a magnetic field. The field causes the rotor to turn because magnetic field in the coil repels the electromagnet. As this happens sparks are generated. These sparks are caused by lots of things but mainly the change in polarity of the contacts as the magnet rotates. Sparks are fast discharges of electromagnetic energy. At certain frequencies em energy is known as radio…

Why does a capacitor suppress the noise?? A capacitor is a component that stores charge. If we want to prevent ‘discharges’ why don’t we store that energy that would be a spark and dissipate it slowly.

Hope this is of some help. Good luck with your experiment…let me know how it goes!

Alex

----- Reply message -----From: “Dave Potts” dave@goopot.co.uk
To: hacman@googlegroups.com
Subject: [HACMan] Robot Hack Question
Date: Wed, Dec 7, 2011 4:45 pm
Thanks for the info. I can see a good experiment here: put it near the tv with and without the capacitor and see the difference. Is there a simple (6 year old) explanation of why it works?
Dave.