Let's Make Robots!

Speedy ATV

drive fast

Hi guys!

Goggling around searching for information on arduinos and robots, I found this fantastic website. After spending hours reading your projects I decided to show you my current project.

It was a RC car that my family gave me as a xmas present a long time ago.

 

atv naked

 

My first idea is to make it autonomous with 2 srf02 modules and an arduino brain, but on the meantime I'm going to play with it changing the controller to digital using 2 xbee modules.

I didn't find much information about the motors but the old board was using two FET transistors 20A rated in parallel and two relays to control the forward/backward movement. I decided to buy two brushed ESC for the motors (one for each) but I think that just the rear wheels are going to be able to move backwards.

As this (cheap 5€ each) brushed ESC cannot switch rotation, I used the biggest relay I found in my electronic-stuff box. The problem, the relay is 24V.

brushed ESC

I make a stepup voltage converter based on a PIC programmer, the original converter gives 13,5VDC from 5VDC. I change something here and there and finally it gives me 28V from 7V of my battery. If someone is interested in the schematic just ask, the ic is a 555 for generating a clock signal.

This converter doesn't give much current but the big capacitor is responsible for the first push and then the battery gives the maintenance current.

voltage converter

As you can see in the photo of the ESCs, one is "naked". It is because this ESC sometimes works sometimes doesn't, I decided to open and resolder all joints (maybe a cold joint). Now it works ok.

 

And now the brain!

arduino brain

 

I am using an arduino mega board with a self made shield. So far the shield contains: 1) LM317 for the 3.3V regulator for the xbee 2) xbee adaptor 3) pins for the servo, front motor and rear motor 4) a transistor for the 24V relay.

I also made a 6-nimh battery pack of 2200mah, not very satisfied with it but it's a start. I'm planning to buy some batteries with pads to solder and make a robust pack not this crappy one.

 

battery pack

 

And finally the theorical speed. Always thanks to google I found this vehicle can reach a top speed of 38km/h, not bad for an oldie ( I believe it won't be easy fast and autonomous).

 

I will be updating soon with a video

Hope you like it!

 

 

 

 

 

 

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The 'selfmade' battery pack was just to test. As you said AA batteries are not suitable for this car, it works when the car isn't touching the ground, but when just a little load on the wheels is put the voltage drops down making the logic reset. I'm planning to separate the power supplies of the motors and servo from the logic. It sucks so much amps of the battery when it hits the wall.

A week ago I ordered a 7,2V 2500mah nimh SUBC battery pack (I didn't believe there were 5000mah available but a little too expensive) I hope it will last longer than the 7,2 nicd 1200mah it used.

About the relay, you're right, sometimes you have to solve things using what you have. I planned using a 5V relay with 2 NO NC poles and able to "open/close" at least 10A current but didn't have any at home but this 24V one.

I've been programming a controller for the ATV in Processing so you can use the mouse to give it the direction and gas. Now I'm finishing the board of the manual controller so it can use the xbee module.

 

Looks like it is coming along. Is it running yet? If so, how about some video?

I have a couple of comments.

  1. I see you made your own NiMH battery pack. I believe the cells in factory made packs are carefully matched so they charge/discharge evenly. It sounds like you are planning to buy a new pack. In the meantime, watch out for your DIY pack to be sure it is not deteriorating or getting hot.
  2. The step-up circuit is pretty cool. However, to me it seems like an awkward way to do it. You have fitted a solution around a 24V relay, rather than getting a relay to fit your purpose. Of course, sometimes you just have to make do with what you have, and I applaud your creative solution. ; j

Good luck!