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30

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 ...


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 have ...


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 ...


9

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....


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 \...


7

Take a look at a kids "spincast" fishing reel and rod. We built one in 2008 (still works, rain, snow and all!) using a automobile door lock solenoid to operate the "thumb release" and an automobile power window motor (PWM & MOSFET) via rubber hose driveline to operate the retract. Choice of MCU is yours, but we've since added spooky lights, MP3 with ...


7

If this is true linear motion (non-rotational) then you will need some sort of a pivoting linkage in between the two units to transfer one motion to the other. Something like this would probably work: As the lower link moves vertically, it rotates the red gear which in turn pushes the second link horizontally. However, given that your image shows more of a ...


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

If you have some budget for your project, both Maxon and Faulhaber have good DC motors and motor-gearhead combinations. Maxon publishes a nice set of formulas and background theory on electric motors. When it comes to getting the maximum performance out of motors, thermal issues are the main factor. One starts asking questions like: What's the actual duty ...


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 ...


7

Your expectations are rather aggressive for a DC motor. First - 40Nm (350in-lbs) is A LOT of torque! Ex: A max rated torque for 1/4-20 bolt is only 75 in-lb (8.5Nm). Second - The mechanical power of a motor results from RPM*Torque. 40Nm*100rpm is 0.56hp (420W at 100% efficiency). That is A LOT, about 1/2 of what today's high end cordless drills can do. ...


6

All very good answers, but as a physics teacher I am concerned about some incorrect equivalences here that can only lead to confusion. One form of [energy][1], eg [chemical potential energy][2], can be converted into other forms of energy (eg [electric potential energy][3], [kinetic energy][4], [sound energy][5], [thermal energy][6]). In the [SI system][7],...


6

I'm not familiar with that platform. But in general, no, you do not need separate batteries for each motor. Also in general, if you need 2-7.5V for each motor, then you probably want one honkin' big battery that puts out 7.5V or slightly more. You could use a 12V battery and take care with your drive commands to never give the motors over 7.5V. Only if ...


6

I think the term you're looking for is outrunner (vs inrunner): This type of motor spins its outer shell around its windings [...] Outrunners spin much slower than their inrunner counterparts with their more traditional layout (though still considerably faster than ferrite motors) while producing far more torque. This makes an outrunner an ...


6

Question 1: If you are satisfied with your robots stopping distance, than you don't need electronic braking. With a heavier or faster robot, its quite useful. The larger the machine, the more inertia becomes a important design factor. For example, a form of electronic braking is used by open-pit mining dump trucks. Ordinary dump trucks, being much smaller, ...


6

It is called a slip ring. It works the same as a brushed motor. See here for a robotic oriented one. Larger versions handle power, and cost more. Also near field technologies such as those used to wirelessly charge your electric toothbrush, and more recent wireless cell phone chargers, are potential solutions


6

Since the open-closed loop issue is already mentioned, I will give a comment to the "I once tried to run a dc-motor without a load". Yes you might damage your motor with this but you can also damage or destroy your motor with a load. The destruction is coming from the current and the resulting temperature. If there is no smoke and some obvious smell coming ...


6

20kg is a mass. It makes a force on Earth (20*9.81 = 196N), but that's not a torque. Motors make torque - what is your maximum torque specification? Once you know how much torque you need (that will be based on the load, gearbox, wheel/pulley diameter, friction and other losses, etc.) then you can ballpark feasibility by evaluating your required torque ...


6

As @szczepan mentions, the difference is one of feedback. There are many ways to get feedback regarding the motion of a dc motor. People implementing a control system will often put a mark on the motor's shaft, or attach a "flag" of masking tape, so that they can visually see the turning of the shaft. This helps to ensure the direction of motion is ...


5

When you PWM the voltage to the motor you are effectively controlling the current to the motor which is related to torque (acceleration). The "jamming up" that you notice is basically the inability of the motor to overcome friction. Think about the PWM as the gas pedal in your car, to get to a constant speed you may push all the way down, gradually back ...


5

If you're saying that it always starts with 80% PWM, but never with 50%, but it runs with 50% after starting, then you're just starting to learn the joys of working with a system that has significant stiction (AKA starting friction). Somewhere buried in this document is a description, along with some prescriptions of how to deal with it in a closed-loop ...


5

The problem is that you cannot control both the voltage and the current. You apply a voltage, and the motor draws whatever current it wants (subject to your ability to supply that current). Alternatively, you make a current controller which automatically adjusts the voltage to maintain the desired current. An analogy would be pushing an object through honey....


5

You can drill a hole to match the shaft into whatever it is and either fix it with a setscrew against the flat or glue it. Or you could glue a brass tube (hobby shop) to the shaft if you can find one that fits. The shaft is 5mm diameter, as venny says. Of course it's easier if you have access to a small lathe (such as Sherline or one of the small Chinese ...


5

There is also ready to use commercial solution from Adafruit, called "slip ring" http://www.adafruit.com/products/736 The only problem is the max speed, which is only 300rpm, but probably you won't get any better with a custom solution.


5

Actually, the caster wheel has ideally no effect on the kinematics of the vehicle. In reality there will be some resistance from the caster wheel that does impact the vehicle motion, but we can still ignore it for the sake of designing a control law. Based on the extended discussion in the comments, your sensor can be used to measure the lateral error of ...


5

Conceptually everything was set up correctly, but a number of basic mistakes affected the signal. Here is the set-up which should be used to record the signal from one of the encoder outputs: A set up like this should result in a a clean signal if your motor/encoder is not broken. Once it's up and running, seeing the signal is simple. It's as easy as ...


5

Model Based: Low cost solution is always software: Develop a dynamic model which computes the load on the motors based on the motions (e.g. with Recursive Newton Euler Algorithm or Lagrange-Euler Method) Make as simple model to handle losses in driver/motor Make the difference between real torque and computed torque It will be not accurate. At least 10% ...


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