# To build a Race Robot !

Need to build a Race Robot

Vehicle(bot) speed must be : 1-1.5 metres/sec

Required Torque : I have no idea how much torque i need BUT it must easily jump through 5cm dia speed breakers(bumps) and should climb a          slope of 40degrees.

Check this out - a sample track -

Robot dimensions : 25*25*25 (l*b*h)

Robot weight: 500 gms  (can be changed if necessary - depending on motors)

Drive: planning for a 4 wheel drive (all four wheels are connected to motors) and Steering front two wheels (instead of differential drive)

Note: None of the robot parts should be readymade (like gearboxes, steering connectors used in rc cars)

Robot must be controlled wirelessly using accelerometer

So, kindly suggest me some specific motors that are good at this stuff and serve my purpose. Also provide some resources regarding the bot construction.

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Hi, Got some questions for you.

1) Which country are you in? For example, if your in the UK, you couldn't use Santosh's advice on the wireless - not allowed to use 433Mhz for this task in most countries.

2) Why do you need 4 wheel drive? It's a pain to produce and harder to code for, and doubles the noise in the system. From what I see of the track, a single motor is more than enough for power - your going to be fighting for weight as it is, and 4x batteries and 4x motors doesn't add any value.

Your plans for steering are going to add a LOT of complexity - the task your trying to do is a simple one mechaniocally, it's the coding and the electronics that are hard - keep the vechicle itself as simple as possible.

3) What dimensions are your bot? if it's mm's it's tiny, but cm would give an odd shape.

4) If you want the steering to be responsive, you need to design from the track width upwards. Start with the width of the track. Have the vehickle maybe 3/4rds the width of the track - unless it's a wide track - if it, just make the bot nice and flat and low. If your jumping, the bot should be as flat as possible.

5) Unless it's a very narrow track, I would *not* use differential steering, just normal ackermann - use a servo to move the front wheel, and put power the the back wheels - the fronts stay free revolving. But.... Do think about linkage design - ackermann does need a bit of planning.

6) How do you plan on working out where the car is positioned? For example, lets say you have a controller in your hands, and you add a direction that says "Go left". How are you planning for the vehicle to know what "left" looks like? A dumb system like an R/C car ( When you get the specific PWM pulse, move the servo +ve 50 degrees ) or a relational system where you would want gyros or similar?

7) When you say "none of the parts should be ready made" what exactly is the scope of this. For example, your 99.99% certain to need to gear down the output from the motors - do you have to make your own gear trains? Does an Arduino board count as ready made?

If this was me, I would start from the track, and that gives the dimensions of the car. You want it nice and low and wide, with the weight near the middle. I would suggest you should keep this as simple and as light as possible initially, as you'll add more complexity to it as you build out features. I would suggest a single brushed motor for power, single servo for steering. I would also, if the rules let you, use an ESC rather than trying to code your own.

Once you have that, build in features as you need them, but for everything keep aksing yourself the question "Is this actually needed, or am I just making things more complex?"

I don't mean this to sound bad, but it sounds like your thinking about a "cool" design, rather than a functional one. The functional one will be a lot easier and cheaper to make, and it's a hard enough thing to do anyway even with that simple scope. When you've got the first one working well, you can always make it cooler afterwards.

I think there might be a language translation problem in the game requirements.

But the way I read this. I think the gist of the rules are that they have to build and race their own RC robots. (can't go buy a RC car)

I believe PF is right in his method to make a custom RC robot that could do this challenge.

If I remember correctly I think the company Velleman used to sell a solder together RC car kit. Its the same RC remote as you would buy from a hobby shop, only in pieces that you have to solder up. Which would supply a lot of goodies to make your robot.

I did a search and found this kit which is cheap online. It could be used for the receiver side (car side) then like PF said, Arduino and a accelerometer for the remote which PWM's an IR LED. Then you wouldn't have any RF concerns.

One more idea, if legal (I don't know the complete rules) but 2 Lego NXT bricks can be used to make a remote control using their built in bluetooth networking. One is the transmitter, the other the receiver. Code samples of NXT-G are online to do this.

@slowsteve  I am in India and this guy is also in India... 433MHz is allowed here.. So there will be no problem in using it..

The 433MHz system doesn't fully matter if its "allowed" in that country, because these radio's are really low power and won't cause interference problems from lack of range/power. They will control a bot inside a room, but not beyond.....I have these exact parts in use right now for a homemade RC tankbot.

I recommend differential drive... because steering front two wheels in a track like this may become difficult ..

To make the wireless circuit I recommend you to use a 433MHz transmitter and reciever that is available in India for just Rs.150 apprx. So you can use them ..

To use the accelerometers u will definitely need two microcontrollers....

Use L298 motor drivers instead of L293D because L298 offers more current than the L293D which means more POWER....

buy a 300 RPM geared motor which is also available in Indian market for about Rs.230 apprx. I dont think that you will need speed for a track like this .. so concentrate on power

And finally the batteries : Use a medium capacity battery like a 2-3AH battery which gives enough power and also lasts till the end of the race ..

ALL THE BEST !

If I were to build this, here's what would be my basic Parts List:

Arduino - you would need 2 of these, or something similar

Accelerometer

Then you would need to make a chassis to put this stuff on.

The Arduino that is the remote gets the accelerometer and radio attached/wired to it.

Throw in some code to read the analog from the accelerometers, which switches the radio buttons.

The receiver side is easy, this radio outputs a simple binary if a radio button is pressed.

So an example would be: button 1 would = forward, button 3 might = turn left, etc.

There are 4 buttons, so the coding is easy.

Hope this helps!

When you say "Robot must be controlled wirelessly using accelerometer" I cant figure out if you are talking about a autonomous or a human controlled vehicle?

hi mogul, its a human controlled robot., we'll connect the accelerometer to our hand and should control the robot by using hand gestures.., up, down, left and right tilt !

Hey, I basically deal with electronics and this bot building stuff is entirely new for me.. Okay, now coming to point, I plan to use brushed geared motors, infact I've seen the 'FingerTech -Spark motors' . Though they are 28 gms i think they should work .. as the bot weght will be 500gms. I am searching in google for these kind of race robots, but at the same time I would expect someone to share some resources if they already had worked with these kind of stuff . . . !