# Why Isn't My DIY DC Motor Turning?

• Engineering
• Benedict Pham
Benedict Pham
Homework Statement
You are to construct a DC electric motor using simple materials. No extra marks can be obtained by using expensive equipment and the use of a purchased kit is not permitted. If in doubt see your physics teacher

Your motor works smoothly and regularly using a maximum 12V power pack or battery.
Your motor is less than 20cm x 20cm in dimensions.
Your motor must be sturdy in construction and easy to start.
The motor must have magnets or electromagnets, a split-ring commutator, brushes and a coil.
Your brushes need to be attached to the motor.
You have used raw materials (where appropriate) in the construction process
Relevant Equations
𝜏 = 𝑛𝐼𝐴𝐵sin𝜃
𝐹 = 𝑙𝐼𝐵sin𝜃
Hi so I'm making a DC motor for my school project and I have no clue why it doesn't work properly. I used copper wire to make the coil (around 50 windings) and put that around a wooden axle (the windings and the coil itself are secured using tape and cable ties), I have a split ring commutator, and I have 2 magnets on either side of the coil. The Magnets are oriented correctly - (NS) Axle (NS) - and electricity goes through it, (it sparks when I put the wire onto it) and it vibrates a bit when I put the wire onto the commutator but it doesn't turn or anything.

Give it a spin with your finger(s) to get it started.
A motor with just two poles can have some dead spots and often will not start on its own.

If that does not get it going, check the rotational relationship between the rotor poles, the commutator, and the magnets. (figure out where in the rotation you want the commutator to switch)

Have Fun!

Cheers,
Tom

Maybe magnet orientation, or external magnetic circuit ?
Please attach a photo(s) of your motor to your next post, so we can see what you have done.
Where we see possible problems, we can ask further questions.

I had a problem once where the connection from the supply to the commutator was inconsistent and the motor only vibrated like you described.

Tom.G said:

Give it a spin with your finger(s) to get it started.
A motor with just two poles can have some dead spots and often will not start on its own.

If that does not get it going, check the rotational relationship between the rotor poles, the commutator, and the magnets. (figure out where in the rotation you want the commutator to switch)

Have Fun!

Cheers,
Tom
Thanks, turns out the magnetic field wasn't strong enough so I added some more magnets and it worked.

scottdave, hutchphd, Mooorshum and 2 others

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