Hi guys, I'm fairly new to Arduino, although I'm almost finishing my first insect robot.
I also have some good C/C++ knowledge. So I was thinking about my next project.
I'd like to build a simple robot with 2 motorized wheels and a third for support, that roams around the house, sucking the dust to a small compartment. Further on I'd add ultrassonic sensors to make it avoid obstacles.
That being said, I have some basic questions:
Which motor should I buy? A 360 degree servo or this one (Sorry I know the ad is in portuguese but all the relevant info should be readable. This motor is very cheap, around 4 USD, while the servo is around 18 USD). I'm concerned that the motor in the ad will be hard to control as I don't plan to install brakes. I will be using the Arduino Uno.
I'm going to need a motor shield, but which one should I buy? I found a 2 slotted one, that delivers a lot of amps and a 4 slotted one but with a 600mA cap. I have to control two motors and power the pc fan I bought (12V, ~300-400mA). The fan will create the vacuum. The servo motor is 6V, 5~6kg.cm torque, current ~300mA I think. The motor in the ad is 5~12V, ranging from 500mA to 1A and can achieve very high RPM.
How am I going to power all of them? Should I buy a 12V lithium battery? I only found an 11V one and it's around 40 USD. Should I wire batteries in series?Is it bad if they have different life durations? How should I control components with different voltages, e.g. 2 servos and a fan? Put the 2 servos in series or add resistors?
Sorry for the tons of questions, all I'm looking is for some basic guidance. I know this is a rather big project to tackle headfirst. But I was thinking of taking it in steps, like first designing the chassis then, plugging the motors with the wheels and making it move around, then add the fan, then the sensors, etc.
Thanks in advance!
Apsan:
Hi guys, I'm fairly new to Arduino, although I'm almost finishing my first insect robot.
I also have some good C/C++ knowledge. So I was thinking about my next project.
I'd like to build a simple robot with 2 motorized wheels and a third for support, that roams around the house, sucking the dust to a small compartment. Further on I'd add ultrassonic sensors to make it avoid obstacles.
That being said, I have some basic questions:
I hope this is just for an experiment, and not for practical vacuuming - because you'll find out just how difficult it is to make a robot vacuum that actually picks up dirt otherwise; it isn't easy.
Apsan:
Which motor should I buy? A 360 degree servo or this one (Sorry I know the ad is in portuguese but all the relevant info should be readable. This motor is very cheap, around 4 USD, while the servo is around 18 USD). I'm concerned that the motor in the ad will be hard to control as I don't plan to install brakes. I will be using the Arduino Uno.
Again - is this for a simple experiment, or as a practical device? Because if it needs to be a practical machine, cheap will only get you so far. Such servos have little in the way of bearings, and what they do have will wear out quickly acting as both a drive system and likely a support (for the weight of the robot) role.
If you need something practical (or even only for experimentation, if you want it to last a reasonable amount of time) - spend the money on servos with metal gears and dual ball bearings on the output shaft, or better - spend the money on larger, higher-quality DC gear motors. Even there, the bearing in such motors need to be respected; it's best to mount the wheels on a proper ball-bearing supported shaft, and then attach the motor to the shaft, either directly, or via belts, chains, gears, etc - so as to take the radial load off the motor shaft (which will lead to failure of the gearbox, depending on the weight of the robot).
Apsan:
I'm going to need a motor shield, but which one should I buy? I found a 2 slotted one, that delivers a lot of amps and a 4 slotted one but with a 600mA cap. I have to control two motors and power the pc fan I bought (12V, ~300-400mA). The fan will create the vacuum.
If using servos for the drive motors, a motor shield isn't needed for them; the fan (since it only needs to turn on or off, and rotate in a single direction) can be easily controlled with a simple switched MOSFET or similar circuit.
If, however, you decide to use DC gearmotors for the drive system - then some kind of h-bridge for each motor will be needed. You will need to size the h-bridge for the size (stall current and voltage) of the motor involved (do not just buy any old driver and expect it to work). The driver should be able to handle the stall current of the motor, plus 20-25% for "head room". So, if you have a motor that has a stall current of 4 amps; then you need a driver capable of supplying 5 amps of current. Note that if your motor doesn't list the stall current, you will need to figure that out first; if it only lists something like "running current" or similar - then figure a stall current of about 10x that - but it is best to measure it first anyhow.
Apsan:
The servo motor is 6V, 5~6kg.cm torque, current ~300mA I think. The motor in the ad is 5~12V, ranging from 500mA to 1A and can achieve very high RPM.
Again, those values look like running currents and not stall currents to me; ultimately, it would be best to either get a clear clarification from the seller, or purchase and measure it yourself. If you use a plain DC motor - you will need gearing for it to turn the wheels.
Also - a PC fan is not going to provide anywhere near enough power to suck up any appreciable amount of dirt, if this is to be a practical device (you could, however, suck up bits of confetti off a desk with it, I suppose).
Apsan:
How am I going to power all of them? Should I buy a 12V lithium battery? I only found an 11V one and it's around 40 USD. Should I wire batteries in series?Is it bad if they have different life durations? How should I
There's a lot of questions here, and my post is already waaay too long; suffice it to say, if you plan on using a lithium battery - do not use any old charger with it, unless you want a fire. Even with a proper charger, lithium batteries can and have caught fire and burned people's houses down. You won't find a 12 volt lithium battery, because the chemistry of lithium cells is around 3.2 to 3.7 volts per cell (something like that). Ideally, you want matched cells (in terms of current capability), and you need a special charger system to charge a lithium battery (called a balance charger - the packs are specially designed for this, with a charge circuit built in - don't try to replicate this, as since you are asking the question, it is way beyond you - I know about this stuff, and I consider it beyond my pay grade).
Apsan:
control components with different voltages, e.g. 2 servos and a fan? Put the 2 servos in series or add resistors?
Don't get funky - for servos, use an SBEC (battery eliminator circuit) to drop the battery voltage down; but make sure the pack will be sized to something close to the motors you are using (that is, don't purchase a large 11.1 volt pack and run 6 volt servos - you're just wasting energy, unless you are going to run a fairly sizable fan for the suction portion).
Apsan:
Sorry for the tons of questions, all I'm looking is for some basic guidance. I know this is a rather big project to tackle headfirst. But I was thinking of taking it in steps, like first designing the chassis then, plugging the motors with the wheels and making it move around, then add the fan, then the sensors, etc.
Thanks in advance!
I hope my suggestions and thoughts will at least get you started in the right direction; you really should do a lot more research on this before making your step-by-step modular plan (the right thing to do, btw - you'll make steady progress, and won't get burned out hopefully).
Good luck!
cr0sh,
Thank you for your very clarifying post. I've learned quite a lot from it.
So now, I have only a few more questions. I hope not to bore you or take much of your time, but you're being very helpful to me.
Do you recommend a particular servo motor? Maybe one that comes with the ball bearings? I would like to make the robot as lightweight as possible.
If I'm going to use the servos, can I stick with my Arduino Nano? But if you tell me an Arduino Uno is better I'll buy it.
I don't want the slightest chance that my house burns down lol. Do you recommend a particular type of battery?
Final question, suppose I use two 6v servos and the 12v fan. Should I stick a 6v battery and use the MOSFET you suggested? Or use 9v? I actually found out the fan turns on with 9v too, probably not as fast though.
As for the robot I was hoping it could suck the dust off my house. It's very thin dust. But even if it doesn't I think it will be a valuable experiment.
Thank you for your patience.
Hi. Im doing the same project although unlike you ive already started.
Im using dc motor and yeah there is the problem of the stall current as well as that the motors were too fast. Ive solved that by supplying PWM signal to the driver. The better choice would have been to buy motors with rotary encoders. Which would also help you in navigating.
For battery you could go with 3x litioun Panasonic with protection on them. (They come like that)
For the vacuum you can just buy the same as the Neato cleaner robot.
It can be controlled with PWM. Its cheap.
Also dont do the same mistake as me by using the l293d for h-bridge that chip sucks!!!
You gotta go with mosfet driver.
Right now ive a problem with the robot for not being able to drive staight, the configuration currently is two dc motors attached to two wheels and two additional helper wheels. I guess the helper wheels are the problem. Should have known to use more ball shaped helper wheels and not cheap ones.
The final problem is how to make the robot navigate through rooms and not clean an already cleaned place. Oh and i forgot to mention im using ultrasonic sensor and servo to move it much like radar and also a dust sensor from Sharp if i remember right
Feel free to get the ideas that robot vacuum cleaner should have. I was able to get best features at http://www.vacuumtop.com/best-robot-vacuum/. Hope this helps! 
Something more at http://automotivespaces.com/. Hope you find information for you.