Motor acting weird

Thread Starter

Man10

Joined Jul 31, 2018
57
I was trying to build a robot arm.

If I don't use a transistor, the electric motor I use will life, a piece of card with a smaller electric motor taped to it, and if I connected the bigger motor to the transistor the motor won't lift the cardboard piece with a smaller motor taped on. I tried using a multimeter, if I don't use the transistor, I get a current reading of 1.35 amp I think, if I use the transistor I get a current reading of 2.64 amps I think. I already used a multimeter to make sure current is flowing. The motor still does not seem to be moving. The motor is a 555 mabuchi. The transistor is a tip110. I will post a schematic soon
 

Thread Starter

Man10

Joined Jul 31, 2018
57
How do I get the motor to lift the arm?
The motor is connected to 1 end of a steel wire the other end is connected to the piece of cardboard with a smaller motor taped on. The steel wire acts as a pulley. The piece of cardboard with a smaller motor taped on is suppose to act as an arm. The bigger motor lifts the arm up and down.
 

djsfantasi

Joined Apr 11, 2010
7,626
We need details about the motors, such as their operating voltage and current rating.

Have you tried running the motors alone with your power source. No wire, no cardboard, nothing connected to the motors.

And some information about how you’re powering the motor. I.e., where is the 3.8V coming from? What is the current rating of the power source or if it’s A battery, what specific battery are you using?
 

Thread Starter

Man10

Joined Jul 31, 2018
57
I tried using 1 lithium ion cell, generating roughly 3.8 volts. I don't think that worked. So I decided to try 2 lithium ion cells connected together, I taped aluminum on the negative terminal of 1 battery and taped the other end of the aluminum strip on the positive terminal of the other battery, so it serves as 1 higher voltage battery. I use that to power the motor. The battery has a voltage of roughly 7.6 volts.
 

Thread Starter

Man10

Joined Jul 31, 2018
57
We need details about the motors, such as their operating voltage and current rating.

Have you tried running the motors alone with your power source. No wire, no cardboard, nothing connected to the motors.

And some information about how you’re powering the motor. I.e., where is the 3.8V coming from? What is the current rating of the power source or if it’s A battery, what specific battery are you using?
I think I tried running the motor alone with my power source, no cardboard, no wire, nothing connected to the motor, it still spins. And if I connect the motor directly to the power source, without the transistor, it will still lift the arm. And if I connect the motor to the transistor, then connect the transistor to the battery, it still won't lift the arm.
 

Thread Starter

Man10

Joined Jul 31, 2018
57
I already mentioned the model of motor is mabuchi 555. Has a maximum operating voltage of 12 volts. It will turn on at 1 volt. Can't find a datasheet on the internet and I looked. Some say the datasheet for this model is not available on the internet.
 

Thread Starter

Man10

Joined Jul 31, 2018
57
The stall current for this model is 2 amps and the tip110 transistor I am using is rated at 2 amps max.
 

MrSalts

Joined Apr 2, 2020
241
The 1Ω base resistor on the base of the transistor is much too low a value. Try somewhere around 39Ω.
LiPo attests are fully charged at 4.2v and the base-emitter voltage is 2.0 to 2.4v per Datasheet The max base current is 50mA. So, worst case scenario is a transistor with a 2.0 Vbe and 50mA means a base resistor of 44ohms (round up to 47 for common size).

Now that it has been connected with 1ohm, it is likely a dead device


Also, the OP should be aware that the pin-out of the transistor is available on the datasheet.

https://www.onsemi.com/pdf/datasheet/tip110-d.pdf
 

MrSalts

Joined Apr 2, 2020
241
Also, those Mubachi 555 motors are typically 12VDC or 9-15v, they don’t have much ltorque below 6v at 3.5v, it wont do any useful work.
 

Thread Starter

Man10

Joined Jul 31, 2018
57
LiPo attests are fully charged at 4.2v and the base-emitter voltage is 2.0 to 2.4v per Datasheet The max base current is 50mA. So, worst case scenario is a transistor with a 2.0 Vbe and 50mA means a base resistor of 44ohms (round up to 47 for common size).

Now that it has been connected with 1ohm, it is likely a dead device


Also, the OP should be aware that the pin-out of the transistor is available on the datasheet.

https://www.onsemi.com/pdf/datasheet/tip110-d.pdf
The 1Ω base resistor on the base of the transistor is much too low a value. Try somewhere around 39Ω.
So why use a higher ohm resistor?
 

Audioguru again

Joined Oct 21, 2019
2,985
Calculate the base current:
1) Base voltage for a TiP110 is typically 1.8V on its datasheet.
2) The 4.2V battery is almost dead at 3.8V.
3) You have a 1 ohm resistor limiting the base current.
4) Then the base current is (3.8V - 1.8V)/1 ohm= 2A.
5) If the battery is working then you destroyed the base of the TIP110 because its maximum allowed base current is only 50mA.
For a load of 2A then the base current is shown to be usually 2000mA/250= 8mA, then the base resistor is (4.2V - 1.8V)/8mA= 300 ohms.
The saturation voltage loss is 1V to 2.5V so the motor gets 3.2V to 1.7V when the battery is fully charged at 4.2V.
 

Audioguru again

Joined Oct 21, 2019
2,985
I usually feel stupid and ignorant about engineering. Thanks for the advice.
Today you learned to lookup the datasheet of a Lithium battery to see that it is 4.2V when fully charged.
You also learned to look at the datasheet of a TIP110 darlington transistor to see that its maximum allowed base current is 50mA and is usually only 1/250th of its collector current when it used as a 2A switch.
You also learned on its datasheet its saturation voltage loss.
 

Thread Starter

Man10

Joined Jul 31, 2018
57
You also learned that a motor rated at 12VDC has almost no turning power (torque) when powered at 1/3rd of its rated voltage.
But I remember when I connect the mabuchi 555 to the battery without the transistor it will lift the arm.
 
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