Author Topic: New to robotics - Some questions  (Read 476 times)

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Offline hichrichTopic starter

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New to robotics - Some questions
« on: October 27, 2013, 04:24:26 AM »
Hello SoR,
I have recently taken an interest in robotics, and I figured I would like to attempt to construct a robot. Basically, I just want to make a remote controlled car - nothing fancy. However, I have no background in this field, so start at the beginning as you answer these questions:
a) Do I need to buy a PCB? If I am making a simple car, do I need to acquire complex software, or can I run it without a PCB and just link up the receiver to the motors?
b) What is the difference between a Servo and a standard motor? (I know that Servos turn 180 degrees, but other than that?) Which would be suitable for powering wheels?
c) From what I have found on the internet, aluminium is a common material for the frame of the robot. Can I use 3mm acrylic? I have better access to the latter.
d) From where can I acquire a remote controller and a receiver? Preferably not a fancy one, just enough to send signals to two wheels.
e) What is recommended for a power source? A rechargeable battery, that provides the right output for two motors. What type should I look at?
f) Is a soldering iron necessary? I found a $10 one at a discount store, which is probably not very high quality. Should I buy one, or can the necessary connections be made without one?
Any help is greatly appreciated to get my project started. Thanks!

Offline gerard

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Re: New to robotics - Some questions
« Reply #1 on: October 27, 2013, 08:14:47 AM »
what is your budget?
if you are looking at hobby-grade rc components, you may be spending a few hundred $$$ on this project

Offline jwatte

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Re: New to robotics - Some questions
« Reply #2 on: October 27, 2013, 12:54:21 PM »
a) By PCB, I imagine you mean "microcontroller" such as the Arduino or Raspberry Pi.
In my mind, it's not really a robot without a microcontroller.
If you just hook up a receiver to motors, then what you have is a radio controlled car, not a robot!

b) A servo is a motor, plus a way to drive that motor, plus a position sensor, plus some logic that drives to motor to achieve some particular position (or velocity.) It is a closed control system, known as "closed loop."
A motor is just something that can generate torque. You need a driver (H-bridge, "ESC" or similar) to actually make it go, and without position sensors (encoders) you don't know whether it's actually going at the speed you want, or if it needs more/less throttle.

c) 3mm Acrylic will likely be too fragile. If you want simple, cheap, and easy to laser cut, I suggest 5mm plywood.

d) A car RC transmitter and receiver combo can be had for < $50 on eBay or various online hobby resellers. Try amainhobbies.com perhaps?

e) RC and robots largely use LiPo batteries these days. For driving most hobby servos and motors, they are intended for 2S (7.4V) LiPo batteries. Older gear wants 4-way (4.8V) or 5-way (6.0V) NiMH batteries which are less finicky to charge, but don't last as long.

f) If you're going to build something that's not already made to be plugged together, a soldering iron, some solder, and a wet sponge will be needed. A plug-in 25W soldering iron as found in discount stores is good enough for putting wires together.

The one thing you haven't listed, that you'll really need, is a multimeter instrument. Make sure it's capable of measuring voltage and continuity ("beep if connection is good") although 99.9% of all meters these days do that.


Offline gerard

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Re: New to robotics - Some questions
« Reply #3 on: October 27, 2013, 09:56:24 PM »

e) RC and robots largely use LiPo batteries these days. For driving most hobby servos and motors, they are intended for 2S (7.4V) LiPo batteries. Older gear wants 4-way (4.8V) or 5-way (6.0V) NiMH batteries which are less finicky to charge, but don't last as long.


I disagree. LiPo batteries have about the same amount of charge/discharge cycles as NiMH batteries (several hundred) . LiPo batteries are much more expensive, dangerous, and complicated to charge because you need a cell balancing charger for it. LiPo batteries are usually only used in high-end RC vehicles that need the most power for its weight. LiFePo batteries are a much better alternative to LiPos as they have several thousand charge/discharge cycles in its life.

Offline Jackson21

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Re: New to robotics - Some questions
« Reply #4 on: October 28, 2013, 04:28:05 AM »
Here's a super cheap LiPo battery that comes with its own charger. Down side is its big, but upside is it has internal protection circuitry, simple to use, on/off switch and simple AC charger. Probably not great quality (I'm still waiting for mine to come in the mail) but for 20 bucks you cant argue.

http://dx.com/p/1268-12v-6800mah-rechargeable-li-polymer-battery-blue-black-12v-227733
Malory: It's okay! They're just blanks.
Lana: Well, see, you say that ..
Malory: But they were blanksóweren't they?
Sterling: Only if the back of his skull picked that exact moment to explode outward.

Offline gerard

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Re: New to robotics - Some questions
« Reply #5 on: October 28, 2013, 08:29:44 AM »
Here's a super cheap LiPo battery that comes with its own charger. Down side is its big, but upside is it has internal protection circuitry, simple to use, on/off switch and simple AC charger. Probably not great quality (I'm still waiting for mine to come in the mail) but for 20 bucks you cant argue.

http://dx.com/p/1268-12v-6800mah-rechargeable-li-polymer-battery-blue-black-12v-227733


LiPo batteries have a cell voltage of 3.7V
obviously something is wrong here...
In no way can you get 12V from 3.7V per cell.
Most 'real' LiPo packs cost between $50-$200 depending on mAh

Offline jwatte

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Re: New to robotics - Some questions
« Reply #6 on: October 28, 2013, 09:35:55 AM »

e) RC and robots largely use LiPo batteries these days. For driving most hobby servos and motors, they are intended for 2S (7.4V) LiPo batteries. Older gear wants 4-way (4.8V) or 5-way (6.0V) NiMH batteries which are less finicky to charge, but don't last as long.


I disagree. LiPo batteries have about the same amount of charge/discharge cycles as NiMH batteries (several hundred) . LiPo batteries are much more expensive, dangerous, and complicated to charge because you need a cell balancing charger for it. LiPo batteries are usually only used in high-end RC vehicles that need the most power for its weight. LiFePo batteries are a much better alternative to LiPos as they have several thousand charge/discharge cycles in its life.

When I said "last as long" I meant that NiMH batteries have worse energy density -- for the same weight, they get you less watt-hours of running capacity.

I agree on the characterization of the other kinds of batteries. LiFePO4, especially, is a favorite of mine. It does require over-charge/over-discharge protection, and it does require a balance charger, which makes it more finicky than NiMH batteries to charge, but LiFePO4 has almost the same energy density as LiPo, and are much less likely to burst into flames, and gives you many more charge cycles of lifetime before they wear out.
And cost more, because of it :-)


Offline jwatte

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Re: New to robotics - Some questions
« Reply #7 on: October 28, 2013, 09:40:10 AM »
LiPo batteries have a cell voltage of 3.7V
obviously something is wrong here...
In no way can you get 12V from 3.7V per cell.
Most 'real' LiPo packs cost between $50-$200 depending on mAh


My guess is it could be a 3S battery, with nominal 11.1V but max-charge 12.6V voltage.
For the kinds of 12V applications they're suggesting (pumps, lights, etc) that difference doesn't matter.
Note that specifications say Li-ion, rather than Li-poly, but the title says Li-polymer.

HobbyPartz has a 5000 mAh 3S LiPo hard-case for < $60: http://www.hobbypartz.com/98p-40c-5000-3s1p-hardcase-direct.html
Whether DX can get it to one-third the price seems... too good to be true.

Offline Jackson21

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Re: New to robotics - Some questions
« Reply #8 on: October 28, 2013, 05:08:18 PM »
Once I get my stuff, I'll run a few testes and let yas know how it goes. I'll also check the quality of the servo's and reg too.

Jacko :D
Malory: It's okay! They're just blanks.
Lana: Well, see, you say that ..
Malory: But they were blanksóweren't they?
Sterling: Only if the back of his skull picked that exact moment to explode outward.

 


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