Core Electronics Forum

Motor or brake to choose


'Hello to all.' I have a project in development where I am looking to make an electric fishing rod. I am looking for the electric part (brake or motor) to make resistance against the fish so that it tires it. What I am looking for is that the shaft that picks up the line can rotate but with a force that I control. As I don't have much knowledge of motors, I wanted to ask if I could use a motor to make it resist, I'll explain with an example. The motor is picking up the line when suddenly a fish bites and makes the shaft turn in the other direction releasing the line. I would like that the motor by means of a signal sent by the microcontroller makes a torque so that it costs the fish. The second option I had thought of is to use an electromagnetic brake so that it only brakes according to a signal. I would like to know if there are motors that can generate torque without being damaged by turning in the opposite direction. Advice, links are helpful. Thanks to all.
3 Likes

Hi Alex
A motor will act like a generator when turned. The resistance to turning can be varied by changing a resistive load on it. This load can get quite hot. It may be a bit awkward and cumbersome for a fishing rod. Up to you regarding that. An electromagnetic brake would probably be more awkward and generate just as much heat. The same amount of energy to dissipate.
Cheers Bob

3 Likes

Hey Alex,

Welcome to the forum!!

As Bob mentioned the power generated from the motor has to go somewhere. In this case, could you use something pre-made such as a bike’s disk brake? With a lever, they are pretty easy to actuate and handle a portion of the heat dissipation themselves from the large surface area.
Putting a motor with an encoder on the end will give you feedback and allow for power to be applied to the reel. I think a way to open the circuit across the motor and close it somehow would be essential to cast the line as well, or a clutch. A relay might be handy!

I’m keen to see what you come up with!
Liam.

1 Like

Hi Alex
Been having a couple of thoughts re this.
Scenario: Line has been cast. Motor reeling line and lure in. Fish bites. Now to stop the line reeling in the fish has to overcome the motor torque and the motor stalls. This will draw a large amount of current from the motor supply with a possible motor burn out.

Before this happens you need to sense the sudden increase in current and switch off supply to the motor. The motor should now be free to turn and become a generator. Load can be applied by connecting a resistor (variable ???) across the motor. As the motor is now rotating in the reverse direction the generated voltage will be opposite in polarity to the supply voltage. By using a suitable diode in series with the load resistor and connecting diode cathode to motor positive and the resistor to motor negative this load can be left in place across the motor and will only come into play when the motor is turned in the opposite direction.

Power can be removed from the motor by using a Mosfet connected as a low side switch and activated by any sensing circuitry used. Or a relay if more convenient. Whatever is used has to latch or you will have a rapid switching on and off of motor power as the current goes off and back on.
Cheers Bob

3 Likes

First I would like to thank Bob and Liam for responding.
I would like to get your opinion on using an electromagnetic brake for braking, I would use it to reduce the turning speed. Can anyone enlighten me on the torque (mN), how much would be advisable for fish between 1 to 5 kg?
The objective will be to brake to tire the fish but without braking at all, this as you have commented may cause overheating no?

2 Likes

Hi Alex

I am no fisherman but as I understand it different fish have different power in their swimming action so good luck with that.

Good luck with that one too. Can’t quite get my head around what you are getting at here. I have always been taught that you get nothing for nothing. This applies to anything. So you can’t slow the line down without some sort of effort. This translates to energy. This energy has to be dissipated somewhere and is usually in the form of heat.

I did not say OVERheating. I said whatever you do to stop or slow that line is going to produce some heat whether it be a load resistor on a generator or brake pad material. The term “overheating” is pretty relative. What may be overheat to one may be normal to another. With electronic bits it is usual to try to keep things below about 50ºC although some things are rated far above this. Some quick tests used to be roughly if it boils or fries your spit it is probably getting too hot otherwise OK.
Cheers Bob

1 Like