Electronic speed controllers and IR LED vs LED

[MeckelBot]

Hello everyone.

First of all, my apologies for any mistake i make using the English language.


I'm developing a school project (much like Ustary ) that can be seen as a line follower with minor changes as to make it useful in a restaurant or similar (it would basically carry around plates from the kitchen to the tables, and come back).

As the title suggests, i currently have two problems, the first being:


Due to torque requirements, we were advised (possibly in this forum) not to use common servomotors, as they are not intended to be used on projects weighting more than a few kilos (ours should be around 14 kg).
So we turned to Brushless DC (AC?) Motors. Since it was pretty cheap and looked good enough, we ordered 2 Turnigy P2627L (already here).

We, lacking a good amount of knowledge or/and experience in the matter, had no idea we would need an ESC for a brushless.

After some quick googling, I'd like to ask,

How is the "programming" made? I've seen some that offer the possibility to reverse the rotation, which is great for us (we had H-Bridges planned, but decided to make sure the robot did the minimum first), but we are clueless on how is that taken care of, or how complicated it is.

Can I assume as BEC output the overall output going to the Motor, and use them for calculations, such as RPMS, etc? Most of them seem to be 5V and when there is only indication of  Amperage, I assume the Voltage is equal to the battery?

We are considering 2 ESC from hobbyking (I hope products from there are trustable ), I don't know if its okay to post links here, anyway, one is referred to as "Hobbyking SS Series 25-30A ESC" and the other "HobbyKing Brushless Car ESC 30A w/ Reverse". Any thing we should be careful about?


Second thing (simpler, thank god) : Originally thinking about Visible Light LED (with LDR as sensors, connected to an analog pin), today I wondered what advantages would we get by using IR LEDs. Any input?


Thanks a lot for your attention, I hope my post was at least mildly clear, and please, any thing the smallest bit useful, please share, it will be appreciated.

[Soeren]

Hi,

[...] a line follower with minor changes as to make it useful in a restaurant or similar (it would basically carry around plates from the kitchen to the tables, and come back).
[...]
Originally thinking about Visible Light LED (with LDR as sensors, connected to an analog pin), today I wondered what advantages would we get by using IR LEDs. Any input?

This will depend on the line "color" as seen by visible light/IR (very often not the same thing). and the "color" of the surrounding floor material. The important parameter is contrast under whatever light you end up using.
You could make a test set-up with both visible light and IR and test in situ.

About the other... Seems you're confusing ESC's (Electronic Speed Control) and BEC's (Battery Eliminator Circuit)?
Make sure the ESC you get is bidirectional. The direction reversal that can be programmed into (some of) them can be used if the motors are mounted mirrored (but this could be done in the software of the 'bot controller as well).

[chuckdaball]

How is the "programming" made? I've seen some that offer the possibility to reverse the rotation, which is great for us (we had H-Bridges planned, but decided to make sure the robot did the minimum first), but we are clueless on how is that taken care of, or how complicated it is.

What type of "programming" are you talking about?  To program an ESC depends on the manufacture, and may require a programming card that just hooks up to the ESC to configure the settings, the ESC should explain how to program it and shouldn't be too hard..  As far as programming a microcontroller to run the motors through the ESC, you just have to send it PWM signals like you would a servo.  As far as an H-Bridge, I believe they only work for brushed motors, or you need a special type for brushless.

Can I assume as BEC output the overall output going to the Motor, and use them for calculations, such as RPMS, etc? Most of them seem to be 5V and when there is only indication of  Amperage, I assume the Voltage is equal to the battery?

The BEC usually powers the microcontroller or receiver along with any servos you may be running. The output of the BEC is usually 5v since most microcontrollers, receivers, and some servos run around 5v, which is different than the voltage going to the motors.  The voltage to the motors is determined by batteries, and you need to make sure that the ESC can handle the battery voltage. You don't have to hook up the BEC part of the ESC if you don't want to.  With your motor and ESC you've linked they should work fine.

[chuckdaball]

Also, let me make a suggestion about the motors you have chosen.  According to hobbyking the motors run around 4400 kv, meaning while under NO load the motor will spin 4400 RPM for every volt you supply.  So if you use a 3 cell lipo, which runs at around 11 volts the motors will spin around 50k rpm.  This is nice if you want high velocity, but provides very low torque.  You might be able to use gearing to increase the torque, but I would suggest something with a much lower kv.

[MeckelBot]

@chuckdaball:

I was lucky enough to notice it too, so we already have the gears and the ratio has been roughly calculated, its time to get our hands dirty now

About the pwm output: cant we do it digitally? correct me if my line of thought is flawed, but we only require a constant speed, so would it be possible for us to set the voltage to the point where the final RPS, considering the wheel diameter, would equal our desired speed, and the acceleration would occur naturally... right? (even if this turns out to be correct, we may still end up using pwm.)

on a side-note: you might be thinking : "why does he want an ESC if he wants a regular speed?" and the main purpose of the ESC is to act as an inverter. Any other suggestion on that problem would be very useful.

I couldnt understand this part: "You don't have to hook up the BEC part of the ESC if you don't want to." I thought the BEC part was the only one going to the motors. So i guess theres another part that connects to them. I cant leave the BEC "floating"?


@Soeren


Considering they are pretty cheap, im going to follow your advice and let reality tell me the best solution .

ive done a quick search on Battery replacement Circuit and it looks like any system you use powered by the regular power plug. That is not what im looking for, though the acronym "BEC" appears on most ESC´s data.

Thanks, ill keep an eye out for that word (Bi directional), but through the board all ESC´s can reverse the rotation? Is it there that PWM becomes specially useful?



Thank you both for your extremely useful (and quick!) help

[chuckdaball]

About the pwm output: cant we do it digitally? correct me if my line of thought is flawed, but we only require a constant speed, so would it be possible for us to set the voltage to the point where the final RPS, considering the wheel diameter, would equal our desired speed, and the acceleration would occur naturally... right

Sorry I really didn't explain this correctly. An ESC works by you supplying it a voltage source, directly from a battery pack, and a control signal, which is usually provided by either a microcontroller or RC receiver.  It's the same thing as providing a signal to a servo with a a pulse command, no difference. The ESC will then use that to control the motor at a particular speed.  You can't, as far as I know, just provide it voltage and have it run.  So you need to be able to find some way provide the ESC that signal. Easiest way is to use a microcontroller, hook up the control signal to it and treat it like a servo as far as programming it.

I couldnt understand this part: "You don't have to hook up the BEC part of the ESC if you don't want to." I thought the BEC part was the only one going to the motors. So i guess theres another part that connects to them. I cant leave the BEC "floating"?

The BEC doesn't control the motors.  It's a separate output of the ESC that provides power to a receiver and some servos.  If you don't need to provide power to them then its not needed.  Sometimes you can buy an ESC without a BEC in it. If you have one on the ESC and don't need it then you can leave it floating.

[MeckelBot]

Sorry I really didn't explain this correctly. An ESC works by you supplying it a voltage source, directly from a battery pack, and a control signal, which is usually provided by either a microcontroller or RC receiver.  It's the same thing as providing a signal to a servo with a a pulse command, no difference. The ESC will then use that to control the motor at a particular speed.  You can't, as far as I know, just provide it voltage and have it run.  So you need to be able to find some way provide the ESC that signal. Easiest way is to use a microcontroller, hook up the control signal to it and treat it like a servo as far as programming it.

I believe i got it now, thanks 

The BEC doesn't control the motors.  It's a separate output of the ESC that provides power to a receiver and some servos.  If you don't need to provide power to them then its not needed.  Sometimes you can buy an ESC without a BEC in it. If you have one on the ESC and don't need it then you can leave it floating.

I do need to provide power to the motors, so I should use a BEC, correct? (how could i not need to provide them power?)

im failing to understand how it works, sorry:  The motor will be connected through the three wires at the same "terminal" (i dont know if this is the correct term) of the ESC, which will provide power, and control him. Ive seen a guy set up a motor once, and i believe he did it this way.
Was that a BEC? apparently the motor can connect to the ESC by two sets of wires, one for control (absolutely necessary) and the optional BEC, so what could have I seen?

thanks

[Soeren]

Hi,

I do need to provide power to the motors, so I should use a BEC, correct? (how could i not need to provide them power?)

im failing to understand how it works, sorry:  The motor will be connected through the three wires at the same "terminal" (i dont know if this is the correct term) of the ESC, which will provide power, and control him. Ive seen a guy set up a motor once, and i believe he did it this way.
Was that a BEC? apparently the motor can connect to the ESC by two sets of wires, one for control (absolutely necessary) and the optional BEC, so what could have I seen?

Let's say your motors run on eg. 12V, so you use a 12V power source (battery).
The ESC handles the speed and direction of the motors AND if it has got an BEC, provides a 5V output to run your microcontroller(s), sensors and what else needs 5V, so you don't need to carry an extra battery (and hence the name Battery Eliminator Circuit).
A BEC stays at 5V while a battery will vary a lot over its discharge.

[chuckdaball]

Here is an image of an ESC.  The three blue wires are hooked up to the motor, they are NOT the BEC.  The thick black and red wires are hooked up to your power supply.  The other cable (red, white, and black) is the BEC and your control signal.  You would connect that cable to the microcontroller or receiver to provide it power and to get the command signal for the motor control. I believe you don't realize that the ESC has more than one output. This is the typical setup for any ESC.

[MeckelBot]

~Thanks! The picture with the description made everything clearer, great.

I´ve been seacrhing for batteries, and this one, which seemed interesting (Turnigy 2200mAh 2S 25C Lipo Pack ) in the picture from hobbyking, shows an exit which resembles a BEC, including a yellowish (signal??) cable. Is it really a bec? whats the point of a signal wire in a battery? and can i ignore it, and plug the two major black and red (you can only see a part of them, but i guess they end in something connectable) on the ESC?

Thanks

[MeckelBot]

~Thanks! The picture with the description made everything clearer, great.

I´ve been seacrhing for batteries, and this one, which seemed interesting (Turnigy 2200mAh 2S 25C Lipo Pack ) in the picture from hobbyking, shows an exit which resembles a BEC, including a yellowish (signal??) cable. Is it really a bec? whats the point of a signal wire in a battery? and can i ignore it, and plug the two major black and red (you can only see a part of them, but i guess they end in something connectable) on the ESC?

Thanks

With a bit of research i believe that plug is the charging plug, am i correct? if so, anything i should be wary of when choosing the charger?

[chuckdaball]

With a bit of research i believe that plug is the charging plug, am i correct? if so, anything i should be wary of when choosing the charger?

Get a charger with a balancer, so it will charge all cells to the proper voltage.  Also get one made for LiPo batteries, since overcharging them can be very harmful to the batteries.  I just purchased a Turnigy Accucel-6 charger/balancer with a IMAX Power Supply from HobbyKing, don't know how well they work since they are currently being shipped, but I have heard good things about it.

Also I would go with a 3S battery rather than a 2S.