# Tag Info

57

Capacitors are used with motors in two different ways. Sometimes the same motor will have both techniques applied, and be associated with two significantly different-looking capacitors. When motors with brushes are running normally, the motor brushes produce sparks, which cause noise "from DC to daylight". This has nothing to do with PWM -- it happens even ...

36

Short answer Stall current is the maximum current drawn1, when the motor is applying its maximum torque, either because it is being prevented from moving entirely or because it can no longer accelerate given the load it is under. Free current is the current drawn when the motor is rotating freely at maximum speed, under no load2 other than friction and back-...

29

I'm posting this as an answer because it is the answer. You can't. As @BendingUnit22 mentions, you are attempting "open loop" control. Noise and variations will mean that your robot will never drive a perfectly straight line. The motors could have different winding resistances (different drive currents/torque), the wheels could be different sizes, the ...

22

I'm not sure if an 'aquabot' is a fully submersible vehicle, or a surface one. If it's a surface vehicle, then you just need to look at RC boats. They've got this solved pretty well. The seal that prevents water entering the boat is called a stuffing box (4 on the diagram). It's simply a tube stuffed with grease. The grease prevents any water leaking into ...

22

You may want to consider a Magnetically Coupled Drive. Use a standard motor with a magnetic coupling to transmit the torque to your prop. This would allow your motor to be completely sealed inside your vehicle: From Eric Stackpole's article mentioned above. Image used without permission, but with attribution. This solution may or may not be suitable ...

18

In theory, you're correct. But in practice, slight differences between the two motors will make them fight each other instead of working in perfect harmony: Even the smallest mismatch in wire tolerances, lengths etc. will create different back emf characteristics due to different impedances. So both will work separately, but the actual ...

17

Stall current is how much the motor will draw when it is stuck, i.e. stalled. Free current is how much current it draws when the motor has no load, i.e. free to spin. As you'd expect, the more strain on the motor, the more current it will draw in order to move; the stall current and free current are the maximum and minimum, respectively. From a standing ...

15

@Ian and @Mark offer awesome (and correct) answers. I'll add one extra point for completeness... There seems to be trend among less experienced designers to assume that stall current and free current equate to the maximum and minimum currents the motor might encounter. They don't. They are the effective nominal values. You can exceed these limits under ...

14

In general, no, it will not hurt the motor directly, BUT, the motor is geared down considerably. This means that when you turn the exterior part that you can physically touch by 1/4 turn - the motor might have actually completed 5 full rotations. The problem can happen when you turn the servo too fast, it may cause gear breakage simply due to excess speed ...

12

If you're looking for a very cheap way to do it (as in, educational budget cheap), check out the Sea Perch ROV build manual. Full disclosure, I used to work at the MIT lab that heads up this educational program. On page 9 of that PDF it starts talking about how to waterproof a hobby motor with a film canister and toilet bowl wax. The entire housing ...

12

The short answer is that you need better control (feedback) to do it. Practically, you will never be able to calibrate the system accurately enough to go straight for more than a few tens of robot-body lengths. Once you dial it perfectly for one set of conditions, the environment or wear conditions will change and you'll have to tune it up again. Surface ...

11

If I were you, I would first (1) read the LM2576 datasheet. I'm assuming you are using a circuit similar to the schematic and PCB layout on page 23 of the LM2576 datasheet. I'm guessing you've tweaked the circuit slightly, replacing the manually-operated pot shown on the schematic for R2, replaced with some sort of microprocessor-controlled thing that ...

11

What Ians answer says about the two motors fighting is true however, I wouldn't go as far to say that you can never put two motors together for more power. In general if the two motors are identical and you are hooking them up and controlling them identically then you can probably get away with it but I would expect some wasted energy and thus extra heat ...

10

The capacitor seen on a lot of brushed motors is there to absorb RF noise due to the arcing as the brushes commutate. You often see these on the motors used in RC cars, where the motors are fairly powerful and spinning fast. The problem comes when you are using PWM to drive the motor. At the beginning of the duty cycle, when the current is switched on, you'...

10

There are two key things to look for from a control system point of view. The first is the root mean square of the torque applied and the second is the following error on moves. Root mean square (RMS) torque As motors degrade over time, they require more torque to be applied for the same acceleration, so if you have tuned your PID loop for a new, low loss ...

10

There are too much of types to someone describe. I think a simple research will help you. Reading the other responses I will put something, to put things like they are. Servo-motor Near any motor can be a servo motor or not. That means a brushed-motor, brush-less motor, stepper-motor (that is a brush-less motor) can be a servo-motor or not. Servo-motors ...

9

I believe this blog has at least part of the answer to your question. Brushless gimbal motor vs. Brushless Motor vs. Servo A user here described the comparison as: A brushless gimbal motor is a regular brushless motor but wound for very low speed (ie lots of turns of thin wire) and many do indeed have more poles. Another post continues: They are ...

8

Gearboxes are probably your best bet if you never want to go fast. You may be able to make it work better if you give it pulsed power (PWM in a way, but pulsed at a speed low enough that the motor actually gets going and then slows down each time. See Controlling Motors in the Presence of Friction and Backlash for details on the technique. You can almost ...

8

This is a standard dynamics problem. Let's use this figure I drew: Some definitions: \begin{align} m & \mbox{, the mass of the vehicle in kg.} \\ \mu_{\mbox{rolling}} & \mbox{, the rolling friction coefficient of your tires.} \\ \theta & \mbox{, the incline of the plane in radians.}\\ g & \mbox{, the gravitational constant, 9.81 } m/s^2 \... 8 How quickly do you want to go from stopped to 10rpm? This will define your angular acceleration. Regarding calculations, first you should convert to standard units, so meters instead of centimeters and radians per second instead of revolutions per minute: \omega_{\mbox{rad/s}} = N_{\mbox{rpm}}*\frac{2\pi}{60} \\ \omega_{\mbox{rad/s}} = N_{\mbox{rpm}}*0....

7

Temperature is a very simple number to measure and is a good aggregation of all the other factors since a weakening motor will be driven harder. Generally a motor that is about to fail will be significantly hotter than the rest of the motors.

7

You'll have to determine yourself whether a motor controller shield is compatible and can be stacked on your existing shield. In some cases, you can use Arduino's SPI. In other cases, you'll need to check whether the pins that your shield uses would conflict with the pins needed by a motor controller.

7

While the answer by freeman01in references a useful presentation (alternative source) on the practical application aspect of your question, it is probably worth answering the specific question in the title too, in terms of first principles. From the Wikipedia Power page: In physics, power is the rate at which energy is transferred, used, or transformed. ...

7

Keep in mind that "heavier" is not quite the term you're looking for. You should be trimming your SeaPerch to be neutrally buoyant, so unless the new payload creates significantly more drag than your old one, your existing motors should work fine (just with decreased acceleration in response to the increased mass). The answer to the question of torque vs ...

7

Let's try and clear things up a little bit... "RC Servo" motors These can be found in radio controlled cars and airplanes to e.g. turn the wheel or actuate various controls in the airplane. They are pretty cheap brushed DC motors, with gears and some sort of crude feedback mechanism. They typically convert an input voltage into a position within a given ...

7

Your calculation of about 80 N⋅m torque for lifting 8 kg with a 1 m lever arm is ok; more precisely, the number is 8 kg ⋅ 9.81 m/s² ⋅ 1 m = 78.48 N⋅m. As mentioned in other answers, you will need to scale up to account for gear inefficiency. A simple calculation based on work shows that the Banebots RS-550 DC motor mentioned in the question is not powerful ...

7

The core reason for choosing harmonic drives is desire for zero backlash. Moreover, regarding mass and size, they become more beneficial for higher gear ratios as their size and mass do not scale for higher ratios. More specifically, they take up very little axial space and use only one stage of reduction. They are beneficial for high precision tasks and ...

6

Your hardware configuration sounds wrong... your trying to provide all the drive current from the arduino Given your description, your using a bipolar (NPN or PNP) transistor, I'd wire up as: Base: To arduino Collector: Motor -ve (motor +ve to Vcc) Emmitter: Ground Alternatively: Base: To arduino Collector: Vcc Emmitter: Motor +ve (motor -ve to Ground) ...

6

A good presentation on how to size your motors for a mobile robot is Sizing Electric Motors for Mobile Robotics from the Central Illinois Robotics Club. The general procedure outlined there includes the following steps: Step One: Determine total applied force at worst case Step Two: Calculate power requirement Step Three: Calculate torque and speed ...

6

There are numerous options that could/should work here. As mentioned by Elias, an IR sender/receiver is a good choice. This is similar to a "break beam" sensor. Essentially, when the beam of light between the transmitter and receiver is broken, the controller knows to do something about it. Similar to this would be an IR distance sensor, which records the ...

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