lightweight, inexpensive speed controllers
 

I was interested in building a quadrocopter, the classic robot enthusiast project. I know generally what to do, except when it comes to speed controllers. The speed controllers used in FRC are way too heavy, too expensive, and require the wrong amount of voltage. I am looking for a light, inexpensive speed controller that can support a 5v input, as well as PWM functioning. Anyone have any ideas?

Re: lightweight, inexpensive speed controllers
 

I'm using http://www.hobbyking.com/hobbyking/s...ontroller.html for mine.

It's not running yet so I can't attest to it's quality but they came highly recommended to me by various sources. Plus, they were cheap enough.

Re: lightweight, inexpensive speed controllers
 

You'll have to provide more information to get good direction out of us :p

What type of motors are you looking to use, brushed DC similar to a CIM in function, or something else? Specs are very helpful.

For your application, using several power MOSFETs would be appropriate. I'd assume your propellers only need to spin in one direction (powered by DC motors), so you wouldn't have to use a full H-bridge.

Re: lightweight, inexpensive speed controllers
 

thank you for the quick replies. Thanks Andrew, that is definitely cheap enough and seems to work fine (as long as you can verify that it does support PWM). As for EFoote's reply, can you elaborate on how to use a MOSFET?

Re: lightweight, inexpensive speed controllers
 

I can confirm it'll use PWM since that's what the arduino I have as my controller outputs and I just double checked the open source code I'm using and it uses PWM.

Re: lightweight, inexpensive speed controllers
 

I'l try to explain as best I can, but I'm not quite sure what your background is / how much you already know.

MOSFET is an acronym for metal–oxide–semiconductor field-effect transistor.

You can use a MOSFET in your circuit as an on and off switch. You would use the PWM output of your micro controller to control the speed of your motor by turning your motor on and off very quickly with the MOSFET, much as the motor controllers used in FRC.

Since your motor only spins in one direction, you only need a single MOSFET to control the motor. The motor controllers used in FRC use H-bridges, which are a combination of 4 transistors.

Here is an example of a single MOSFET driving a motor. By varying the duty cycle of the PWM signal, the motor's speed can be controlled.

EDIT:source - http://www.picotech.com/applications/pwm_drivers/

Re: lightweight, inexpensive speed controllers
 

the picture is broken so I can't see it, but I think I know kind of how it works. Because PWM by its design is pulses, a MOSFET just sends out 5v whenever it gets a positive signal from PWM?

Re: lightweight, inexpensive speed controllers
 

i've run that esc on a battlebot. they do pretty much exactly what the descriptions says.

soft start is annoying if you are trying to start with a heavy load on the motor and go full throttle but otherwise i can't complain.

yes they are pwm based.

Re: lightweight, inexpensive speed controllers
 

It depends on the MOSFET, but yes, sending a high signal will either turn it off / on.

Also, very important in the image that I haven't described yet is the snubber diode. Since a motor is an inductive load, simply turning it off while it's running is enough to destroy most MOSFETs / circuits.

Re: lightweight, inexpensive speed controllers
 

thanks for the pointer about the diode. finally, any suggestions about specific mosfets to buy (don't forget, will be operating at 5v)? and do i need to use resistors at any point, whether from the PWM signal etc.

oh, and is a "snubber diode" a specific type of diode or will any type do?

Re: lightweight, inexpensive speed controllers
 

Have you played with transistors before? A MOSFET, as mentioned earlier, is a very high powered transistor. Typically, though it is possible not to, you would have a filter capacitor attached. When the MOSFET is turned on, it will fill up the capacitor a little. If the MOSFET is on a greater portion of time, say, 1 second, the motor will get more power, and thus spin faster. However, if you have the MOSFET on for a lesser portion of the second, the motor would get a lower power and be slower. This will only work on brushed motors, and maybe those brushless motors with a built-in controller, like the ones in the computer you are using. If you are using brushless motors, like most quadcopter builders, you would need an ESC, a speed controller meant for brushless motors, much like the ones Andrew suggested. Also, why are you running 5 volts? What Battery technology are you using? If you are building a small flying machine, 3.7 volts (1s LiPo) may work. However, for most medium-large quadrotors, 7.4v (2s LiPo) or 11.1v (3s LiPo) would be optimal. If using Arduino for the controls, have a 5v regulator powering the control system, but have the motors/escs running off unregulated voltage. The ESCs that Andrew suggested have a built in UBEC (Universal Battery Eliminator Circuit), a wierd name for a buck voltage regulator, rated for 5v, 2 Amp. That should fall aplenty to power your Arduino and any other circuits. Some of these can severely reduce your cost, without reducing your quality. As a matter-of-fact, you may be able to get a better quality than those expensive ESCs from HobbyKing!

I would like to know what is your prefered power source, to help you get better information

Re: lightweight, inexpensive speed controllers
 

They are programmable, perhaps it's an option to turn off soft start? It's not really an issue for me, I shouldn't ever be going to full throttle suddenly.

Re: lightweight, inexpensive speed controllers
 

yeah there is way to turn it off. i just wanted to point out that soft start is a thing because i was having cogging issues and thought it was the motor for the longest time before i tried disabling soft start.

Re: lightweight, inexpensive speed controllers
 

As far as I can see, that speed controller is meant for 3-phase motors, AKA. brushless motors. That's why there are two input wires and three output wires!

Re: lightweight, inexpensive speed controllers
 

yea I'm stupid with the voltage thing. wanted to only have one power source, but that wouldn't work too well.

Re: lightweight, inexpensive speed controllers
 

I deleted my post about the brushless motors because i looked it up and realized that I definitely do not have brushless motors

Re: lightweight, inexpensive speed controllers
 

what type of capacitor would you recommend?

Re: lightweight, inexpensive speed controllers
 

Please elaborate. What is your power source?

Also, you were wondering about the capacitor: any capacitor will work. In this case, you probably would like a Electrolytic Capacitor. Make sure the voltage ratings are 3 TIMES the max voltage of the qc. 1000uF - 5000uF should be good enough for a filter cap. Also, don't forget the protection diode. Make sure the diode is set up to only allow current in one direction, to prevent reverse current!

Re: lightweight, inexpensive speed controllers
 

I didn't do anything yet, still in planning stage, so I wasn't exactly sure how to power it yet. I wanted everything to be run off of the same batteries, but it is now apparent that I would need to have 1 set for the controller and 1 for the motors, etc.

Re: lightweight, inexpensive speed controllers
 

NO. You need an UBEC. That will reduce the voltage of the main battery to 5V for your Arduino. This is what you are looking for! Otherwise, you can always hook up ye olde' 7805 or LM2940 to power up the controls! I am not an Arduino user. I've been taken by Parallax. However, if Arduino has the regulator built in, it would be horribly inefficient. Make sure to use VDD, not VIN, if using a UBEC!

Re: lightweight, inexpensive speed controllers
 

nah man you don't need multiple batteries, you need a BEC
it steps voltage down to 5v


if you are looking at loads under 7a you can hack the vex motor controllers


guide to hack

Re: lightweight, inexpensive speed controllers
 

Well, if you're still in the planning stage, you need to first figure out what you want as the end product, and then you can begin to fill in the details of how to get the end product.

So, let's start with the quadrocopter itself. How big of a quadrocopter do you intend to build? How long do you want to fly it in one go? How much are you looking to spend? Those three questions aren't mutually exclusive, but if you can answer them it'll definitely help us determine the scope of your project.

Once you answer those questions, we can move on to something like the power source. Based on how light these things need to be, you'll probably be using some sort of Lithium Polymer battery. Based on that chemistry, there are several voltages you can pick be it 3.7v, 7.4v etc.

You'll be using unregulated voltage (directly from the battery) to power the motors. Which are also important. Based on the size of your quadrocopter, what motors do you need to power it? The motors you pick will determine what kind of motor controller you can use.

Once you know these things, you can start to focus on what's controlling it. It's fairly straight forward to design a power supply for the rest of the circuit (micro, sensors, etc), but you'll need to pick each one of those components out.


As you can see, there is a lot of thought that goes into a project like this, and it's better if you first understand and describe the basics (such as size) before asking for help on a minor detail (motor controller).
Unless you're trying to guestimate the cost, which asking for prices of motor controllers might be appropriate.


____
EDIT:
I'm not trying to discourage you! This sounds like an awesome project, and I'd love to see you follow through with it. We just need a bit more information to be more helpful :D

Re: lightweight, inexpensive speed controllers
 

Let's go with some more details!:
-How much do you want to haul?
-*Flight Time per charge
-Size
-Weight
-Power Rating (~200w/KG)
-*Price range
-other features

*=Mentioned by E. Foote

Re: lightweight, inexpensive speed controllers
 

I just finished up my senior design project and it was based around a quadcopter. There is quite a steep learning curve when you get into it all.

First and foremost, what do you currently have on your list of parts for the quadcopter you want to build?

Re: lightweight, inexpensive speed controllers
 

I'll have to say, for the QC, here's what you will need, minimally:
-Frame (can build yourself)
-Motors(4) (Brushed/brushless. brushless if prefered because brushes wear out quickly at that RPM)
-Battery
-ESCs(4) (one for your motor)
-Control system (Arduino, with gyro)
-Propellers(4) (Depends on size of frame and weight)
-BEC (5V for Control System)


-And, don't forget those blinkies :D
-You put those together and you have a UFO when flying at night! :D

Re: lightweight, inexpensive speed controllers
 

I'm going to add that brushless motors are a must. The way a brushless motor operates makes their speed much more controllable than a brushed DC motor.
There are also ESCs with a BEC built in that provide power to your flight controller.

Re: lightweight, inexpensive speed controllers
 

Before moving too far ahead with your project using FRC based knowledge, I strongly recomend boning up on modern RC build practices. I've built several quads and RC planes, and the difference to FRC is night and day.

If you're doing this on a budget, HobbyKing is going to be your best friend. Their forums have a great write up to get started in quads: http://www.hobbyking.com/hobbyking/f....asp?TID=38561

After that, there is a rather lengthy post about building your first quad here: http://www.hobbyking.com/hobbyking/f....asp?TID=18772

A few last minute tips from my own experience:
Always fly in an open area, since trees suck to crash into.
Don't go as big as possible for your first quad. These things are tough to learn to tune and fly; starting on a smaller platform is much easier.
And last but not least, be very safe. Always treat it like it will turn the rotors on at any moment.

Best of luck.

Re: lightweight, inexpensive speed controllers
 

If I were to approach this problem, I might start by looking at what's available to the average consumer / near hobbyist level. I believe brushed DC motors are used on the popular Syma S107G model and knockoffs, and searching Ebay I can get a pair of them from China for $6 (including shipping).

One could also try to cannibalize more of that helicopter to get appropriate (and proven) gear ratios, as well as mounting hardware.

Controlling a brushless DC motor is not trivial, which is to say that as a hobbyist you wouldn't build one from scratch as you might an H-bridge or other brushed DC motor controller.

Re: lightweight, inexpensive speed controllers
 

One of the guys at my local space has a series of nasty scars up his right side from when his quad turned on and the blade caught him. Turns out CF blade vs skin… the CF wins by a lot.

Don't forget these are machines with a simply crazy amount of power.

When working with your batteries be careful not to short them. Be careful flying near people, even a small quad dropping at someone can hurt.

Re: lightweight, inexpensive speed controllers
 

Bottom line is there's a ton of stuff already done for this particular application and you probably want to at least start with what is readily available and in widespread use. The underlying technology is similar, but you most likely do not want to try to build your own controller -- lots of optimization has already been done, just as for motors for this application. The terminology is different and seems to come from the RC plane/heli world. You want an "ESC" where you ask about motor controller and yes, these use PWM -- same RC background, which is really where PWM came into FRC I suspect. This is how most traditional RC systems send control signals over the air. And the motors need to run directly from the batteries, with the "battery eliminator" to supply power to other electronics that needs different voltage(s).

BTW, the reason for this is the same reason you don't try to regulate the voltage except by turning it on and off very quickly: trying to control voltage other than just on/off means turning power into heat / lower efficiency. You don't want low efficiency in anything that is battery powered, not that you ever really want this in anything besides a heater.

Re: lightweight, inexpensive speed controllers
 

Are you programming this yourself? If so, it will be complicated because I am implying that you have no flying experience. You might try a KK board controlling the copter, being controlled by the Arduino. The KK board will stabilize the quad and do all the important functions. The Arduino can be the controller. You may wind that easier. How much experience do you have in Arduino programming? I would use something like the Propeller chip because you can code the multicore environment to do the flight controlling in a core, and the rest of the stuff in another! However, this all is based on what MCU you are most experienced in using!

Also, using a linear voltage regulator at those currents would cause the magic smoke of death to puff out of the regulator. Powering my RasPi from an LDO gets the chip so hot, I have it connected to the aluminum chassey of the robot for a ginormous heat sink!

Re: lightweight, inexpensive speed controllers
 

Don't even need CF. The APC props on my quad sliced through my finger like butter.

Re: lightweight, inexpensive speed controllers
 

Depending on the current draw of the controller, as well as the supply voltage of the battery, a low dropout regulator may be just fine. Basically what you need to remember is the difference in the battery voltage and supply voltage is just waste at the linear regulator.

If you have a 12V battery with a 5V linear regulator, drawing 700mA from it will cause it to act as a 4.9W space heater (gets hot very quickly).
If you have a 7.4V battery with a 5V linear regulator, drawing 50mA will only waste .12W, which is much more manageable from a power dissipation perspective.

Re: lightweight, inexpensive speed controllers
 

Yeah. Thee Arduino should draw about .2-.5A. The Gyro and other sensors may use up more, so you may use close to 1A/Hr!

Re: lightweight, inexpensive speed controllers
 

An Arduino running at full tilt will only consume about 20mA, and only 12mA of that is the Atemga itself. Gyros will pull maybe 4mA (x3 though). Toss on an LCD like the KK2 model uses (which I HIGHLY recommend), and your power budget for the control board is still in the sub 50mA range.

On a quad, or any aircraft, the bulk of the power is consumed in the motors, and the rest is such a small percentage you can basically ignore it. With a 20A ESC, that control system is taking less than one percent of the total power. A small UBEC will work just fine.

Re: lightweight, inexpensive speed controllers
 

It is about 100 times easier to do it properly and just buy the correct hobbyist gear. The pager motors used to drive the $30 mall helicopters are nothing compared to the brushless hobbyist motors that are *very* easy to use. This stuff is meant for casual users, so it is way easier than trying to hack the cheapo helicopters. (not that that isn't fun too)

General note for people purchasing R/C toys: Buy the real thing! A $100 beginner heli from Horizon Hobby is more durable and orders of magnitude more controllable (and thus more fun) than the cheap-o ones at Brookstone.

/Soapbox

Re: lightweight, inexpensive speed controllers
 

Ryan,
This is really a much more simple project than what you have been thinking. Your motors are only going to run in one direction and then only need to be controlled for speed. In brushed motors, it is a simple matter to control the drive current to control speed. A simple amplifier is all that is required. Either a transistor or MOSFET can be used. It is also possible to control the speed by controlling the on time of the transistor which is also easy to accomplish with a micro-controller doing all the control. The transistor then becomes a simple switch turned on and off by the controller. MOSFETs are usually the device of choice since they have a much lower "on" resistance and therefore are more efficient. No caps are needed in this case. Usually a simple resistor and the transistor are all that are needed. The three terminal regulators (7805) are available in small packages (TO92) to supply the controller. And they are very cheap.

Re: lightweight, inexpensive speed controllers
 

Use Brushless motors. With the controller, they MAY cost a little more, but will be around the same price range. At those high RPMs, brushed motors are going to rip their brushes off! It will be easier to control brushless motors, as compared to brushed motors because brushed motors don't react to signals linearly, so the small irregularities in the motor will cause them to react differently. With brushless motors, you get absolute control because these motors are commutated by you, so you can possibly set the exact RPM you want! In other cases, you could use an encoder on the brushed motor. However, that would still be quite hard to program correctly, especially on the Arduino. The amount of data coming in from the encoders could be so much that it could overwhelm the DSP!

Re: lightweight, inexpensive speed controllers
 

FRC is an "Engineering Competition". I know your quadcopter is not for FRC but the same though process apply.


The answers to these questions are not rocket science but to properly address them (and the interactions between these choices) would require more than a few posts on a forum like this. If you were in the Houston area, I could help you out. Otherwise, there may be a hacker/maker space near you with someone who has hands-on experience doing this. If you are feeling adventurous, you might consider reading application notes from MOSFET manufacturers such as Fairchild, Infineon, Vishay and others. If you really want to get into it, there are books such as the one by Mohan that are classics in the power electronics field (http://www.barnesandnoble.com/w/powe...an/1101194755). Unfortunately, quite a bit of the advice you have been given in this thread will likely cause the release of a lot of "magic smoke" and lead you to waste time and money.



Even though I design large motor controllers for industrial applications in my day job, I would still buy a ready made one for a project like yours since it would be very difficult for me to beat the price. You have more than enough challenges to overcome in other areas of your project.


I think these are the ones that several of my co-workers use for their electric airplanes and helicopter.

Re: lightweight, inexpensive speed controllers
 

I will more-or-less have to agree with you in many ways and disagree in a few ways. The fact that you mentioned, that you need to go by the same engineering process as in FRC is nothing but correct! Ryan, you may want to skim through this. However, where you said that a lot of stuff we told Ryan wouldn't cause magic smoke to appear, if done right. And yes, this ISN'T rocket science (though that is just an exaggeration because rocket science isn't as hard as developing a nuclear reactor) :D. Also, what is this company you work in? I am designing a microcar, and I am having a difficult time in finding a good speed controller that is a lot more advanced than those crappy DIY ones available! Everything will be controlled by MCUs, like the QC we are talking about!

Ryan, after you build this with Arduino, I'd like to see you post a video of it, and for a challenge, you should place an RPI doing vision tracking to automate this QC! :D

Goog luck!

Re: lightweight, inexpensive speed controllers
 

Yash

You are welcome to disagree.

I am interested in what process you used to arrive at the component selection recomendations you have made regarding the MOSFET, capacitor, diode and regulator. Please also post a schematic showing how you feel these components should be connected to clarify your descriptions in your previous posts in this thread.

There are a number of manufacturers of motor controllers for the EV conversion market. In your thread about your microcar, I had already directed you to your local branch of the HEAA where it is much more likely that someone with the appropriate expertise to help you.

I am not aware of Toshiba manufacturing any 3-phase motor drives suitable for the automotive market. If they did, there would be an exclusive supply agreement with an OEM such as Ford or Toyota and one would only be able to purchase those drives from a car dealership. If you are really curious, the following is a link to one of the products that I have been doing R&D work on. These are aimed at heavy-industrial and oil-field applications.

www.toshiba.com/ind/product_display.jsp?id1=7&id2=861

Re: lightweight, inexpensive speed controllers
 

Please pardon if I accidentally restate something that has been previously said, I have foolishly not taken the time to read ALL of the replies yet.

I have been working on a similar project, but instead of a quadrotor, I'm building an ROV (underwater). Basically, MOSFETS are the way to go for a small, compact yet extremely powerful speed controller. Here is a video that helped me a lot in understanding MOSFETS that I hope will help you. I strongly recommend checking out the other videos in the series; they are very valuable and well thought out electronics tutorials.
http://www.youtube.com/watch?v=CFt8h...ACE&index= 26

If you use MOSFETS, you need a snubber diode and really should have some capacitors for decoupling and signal noise reduction. You should use a tiny ceramic cap for very fast reactions paired with a larger electrolytic cap to handle the large loads.

I can send eagle files/circuit diagrams if that would help, just pm me.

Re: lightweight, inexpensive speed controllers
 

The video is a nice discussion but the diode in the power MOSFETs is a fall out of the manufacturing process. The FETs used in our speed controllers all have them. The real benefit is the very low ON resistance source to drain compared to a normal transistor. One of the effects of the diodes is that the speed controllers light up when you push the robot with the power off. The current generated by the motors turning, ends up passing through the diodes and out to the power supply.

Re: lightweight, inexpensive speed controllers
 

I want to put this in a 4S quad :). I love magic smoke :D

That's what I call the king of batteries! I searched HobbyKing and this is their biggest battery :)

Btw, I bookmarked that channel cause I liked that video!


I think that you will like this, Ryan:
http://www.hobbyking.com/hobbyking/store/__26944__IDEAFLY_IFLY_4_Quadcopter_with_Motor_ESC_ Flight_Controller_PNF_.html

I forgot how I got the link. Maybe I found it on this forum?!