Wednesday, October 21, 2015

How Do I Robot?! Part 2 + Meet The Builders #2

Building on the last instalment today we dive into control systems and motor controllers!
Sorry for the delay, this is the 3rd time I've had to re-write the article.

But first don't forget to checkout http://sparc.tools/
Not only is it full of info for new builders but is a virtual meeting place for a majority of combat robot builders the world over!

Last week we told you about the 4 components needed for any robot.

1: Motors
2: Batteries
3: Control system
4: Motor controllers

With these 4 basic components you can build robot. Without them you will certainly have issues.
We asked Idea Factory Labs a rookie team to take part in our second Meet The Builders Instalment.

Team Idea Factory Labs 11pm Sept 18th
Cameo by ShaunZ of Team Orbital Spin in the back!


Idea Factory Labs is a new team who had plans to build and enter a 30lb sumo robot for Event #1 at Maker Expo. Unfortunately they lacked one of the 4 critical parts and try as we might we could not get them online for Sept 19th. 

Here's their take on the success and failures of their first 30lb robot Revered Rust Bucket. 


As Andrew said, time is always a factor but without the basic parts its difficult to make progress.

So here's what you need to know.

- Control System -

When it comes to sumo bots you have two options
-Tether
-Radio Control

What you decide here may effect what motor controllers you need.

Lets talk about tether control.
What is involved:
1) Control box
The drive uses a control box with a number of analog switches on it
2) Signal wires
Low voltage signal wires run from the control box into the robot. (This means you have a physical connection with the robot)
3) Motor controllers ESC/Relay (more on this later)

Here is a handy intractable on a simple tether controlled robot.
http://www.instructables.com/id/Wired-control-robot-manual-4x4/

Items 1-2 are fairly simple so lets look at Item 3, motor controllers regarding tether control.
Depending on your operating voltage you may be able to use simple switched attached directly to the robots motors like in the above instruct-able. However it is more likely you will need to use relays.

Relays are easy to use electrical switches, by applying a low voltage and current say 5v and 500ma you can turn a relay on (or off). In doing so the relay then allows a higher voltage/amperage to pass through its circuit, say 24v 10amp.

Using a relay allows you to use safer power levels in your control box and keep the high power stuff in the robot.

Why can't I just run 24v and 20amps to my control box with switches?
Because its against the rules!

 Automotive relays can be had for under $5 each and operate on 12v.

Standard relay: Will drive a motor in 1 direction
For forward and backward control you will require 2 relays.

Reversing relay: Will drive a motor in 2 directions
For forward and backward control only 1 of these is required.

Here is a quick list of single and double through relays.
-12v Reversing Relay
-24v Reversing Relay
-12v Standard auto relay

Here is a little diagram showing how relays work!


Imagine the light bulbs as motors and you can see how this might work in a robot.
Its worth mentioning however you would have to remove one of the light circuits. You will notice with this circuit one light is always on. This means if you replace the lights with motors then 1 motor will always be running.

Now lets tackle Radio Control

 What is involved:
1) Radio transmitter
2) Radio receiver
3) Motor controllers ESC/RC Relay (more on this later)


RC transmitter and receiver

For purposes of this discussion we are going to assume we are using off the shelf components and not custom built radio systems.

First thing is you need a radio system. Stick to the following frequencies:
-FM 75mhz
-PCM 75mhz
-2.4ghz

Other frequencies such as AM or FM 72mhz are not suitable for ground based robots or unsafe due to  interference issues. Also avoid simple RC toy controllers.

A complete starter radio system can be had for less then $50
http://hobbyking.com/hobbyking/store/__43854__Turnigy_5X_5Ch_Mini_Transmitter_and_Receiver_Mode_2_.html

Your transmitter sends out a radio frequency which is then picked up by the receiver. The receiver then turns that signal into an electrical pulse (RC PWM). An electronic speed controller, ESC can then use that RC PWM signal to control a motor.

Here is a little setup picture of a basic RC setup.


- Motor Controllers -

 Now its the big and more confusing topic. How do I drive my motors off an RC rig?!

Use an electronic speed controller (ESC) or an RC Relay

An ESC is a little circuit which interprets the RC PWM from the receiver and uses it to drive a motor.
An ESC allows you to run a motor from 0% to 100% and everywhere in between for proportional control.

When choosing an ESC consider the following;
-Motor Voltage
-Motor amperage

Lets assume we're using this motor:
http://www.robotmarketplace.com/products/AME-206-1004.html

According to the specification sheet this is a 12v motor with a stall current of 23amps.

The stall current is theoretically the most current this motor can draw, so our ESC should be able to handle a minimum of 23amps (lower and we risk damaging the ESC).

Here is a list of popular 30lb combat robot ESC's which would work in this instance
-BotBitz 30amp
-Talon SRX
-Ragebridge
-Roboclaw 2x30
-Marine Controller
-Scorpion XXL

A single channel ESC like the Talon SRX or BotBitz 30amp will drive 1 motor forward and backward.
A 2 channel ESC like the Ragebridge or Roboclaw 2x30 will drive 2 motors forward or backward independently.

For instance I use a Roboteq AX1500 2 channel ESC in my 120lb robot. This allows me to use 1 circuit board (AX1500) and run each set of drive motors of my robot independently.
Being able to run motors independently is important for a robot with tank style steering.

What is tank style steering?
The robot below has 2 wheels and 2 motors, one on each side of the robot. By altering the direction of these wheels the robot can drive forward/backward or turn.




What is an RC Relay?

An RC relay is kind of like a dumb ESC, it has a small circuit onboard which can read the RC PWM signal from the RC. When the signal from a transmitter is given the circuit in the RC Relay will open or close said relay.

 Here is an example of a motor control circuit with an RC Relay.


Just remember, when relays are turned on they give the motor 100% power. This might make it difficult to drive.

The circuit above will allow you to remotely drive a motor in a single direction. You will need another RC relay wired slightly differently (with diodes) to drive the motor in the opposite direction.

Here is a list of RC Relays:
-Battle Switch
-Double Battle Switch (useful for running forward/backward)
-TD Relay (useful for running forward/backward)
-Pololu Relay

This should be more then enough to get to get you moving!

If you have more questions feel free to email, tweet or join our Facebook Group!

Until next time!

-Ravi B
All Black Robotics

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Friday, October 2, 2015

How Do I Robot?!

We've noticed a lot of google traffic searching for parts and insights into 30lb sumo robots. 
With that we decided to put out a little info to get you new builders started.

Don't forget to check out http://sparc.tools/
Not only is it full of info for new builders but a virtual meeting place for a majority of combat robot builders the world over!

You need a minimum of 4 parts for any robot.
Ravi Baboolal of All Black Robotics talks about the 4 components needed for a 30lb robot. 

1: Motors
2: Batteries
3: Control system
4: Motor controllers


 - Motors -

Realistically the aspiring builder has two options when selecting drive motors for a robot. 
A) scavenge / repurpose
B) purchase new

Which ever way you go it's good to keep in mind that you will likely need a gearbox or gearing system. A gear system utilizes gears, pulleys or chains to reduce the output of a raw motor into something more useful. For instance, the E-scooter motors I use on my 150lb robot Roach have an output of 2750 RPM (revolutions per minute) had I attached a wheel to that motor the robot would have had little pushing power but moved at 30mph...much too fast to be of use. 

Instead I used a series of timing pulleys and chains to reduce the motor output to something useful (1000 RPM) all while gaining much needed torque for pushing other bots around.

For an in-depth look at how gearing works check out;

Scavenging

Scavenging motors is an affordable way to go, though this doesn't mean digging through piles of trash looking for the perfect motor (most of the time). But rather repurposing readily available options such as cordless drill motors, E-scooter motors or car window/fan motors.

Cordless drill motors can be a great option, they are built to be powerful, lightweight and perfectly suited to run off DC power (battery packs). The drill motor itself comes with a gearbox which amplifies the motors raw power into something more useful.  The trick to working with these is they can be difficult to mount to a robot frame and have a threaded output shaft. However these issues are not insurmountable. There are a number of ready to use wheels and hubs which mount directly to a drill, otherwise you can mount your wheels to the motor with nothing more then a drill and the right thread cutting tap.

For details on dissembling a drill check;

Purchasing

If you'd rather buy a purpose built gear motor there are now many options built specifically for fighting robots. Check out the following websites;

Quick recommendations for the 30lb class; check out the Banebots gear motor and wheel combo

 - Batteries -

We could take an entire week to go through battery details. But I'm going to make this quick and easy. First thing you must do is select a voltage, this usually depends on the motors you're using. So lets say you've settled on 12v drill motors motors. Now we need a 12v battery with enough capacity for our robot. 

Here is a nice little tool for determining how much capacity you need, capacity is measured in Ah or Mah (Amp Hours / Miliamp Hours)

Lets say, 2x 12v harbour freight drill motors with 3" wheels 
This is a fairly common set-up.

The calculator will spit out a number, in this case 0.11Ah to run for 3 minutes. Meaning we need a battery with at least 0.1Ah or 1000Mah capacity. For this I may select a 12v 5amp sealed lead acid battery.

Like this;

At 6Ah we should be able to run for a lot longer then 3minutes too! 

You have a number of options when it comes to batteries. Generally select the battery with the highest capacity you can afford so long as it will fit in the robot.

Here would be a few other options:

or one of these

Battery Chemistries; 
NiMH
NiCad
Li-Poly
LiFePo4
SLA

For reference I used 2x 24v Nicad battery packs to run my 150lb robot Roach. The battery packs were run in parallel equating to 7.2Ah which gives me 10-15minutes of run time.

Which ever you select please research the battery, how it needs to be charged and the equipment required to do that. Most batteries require special charging equipment. 

Here is a little intro video for RC batteries;

Next week we'll cover Control Systems and Motor Controllers. 

If you have design or component selection questions do not hesitate to reach out via Facebook, email or twitter!

Until next time.

-Ravi B 
All Black Robotics



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