Building an RC Car Update 5/27

Hey all,

There are many updates! I have been working on the revised motor controller circuit board for weeks now. If you remember, I shared the screenshots and rendering of the original motor controller PCB a few weeks back. However later on, I decided to integrate the C2000 Launchpad, all the pin outs for external components and the motor controller on the same circuit board. So I have been working on this revision and here it is! The following pictures are OSHPark renderings along with 3-D image renderings. Let me know what you think! OSHPark quotes me $60 for 3 of these boards but it looks like I can get 5 of these boards for about $20 from Seeed Studio.

3-D Renderings of the Board. Notice the two sets of double headers where the Launchpad will sit on. 

OSHPark Renderings of the board.

Before I send it out to the fab, I still need to do a few more proof of concepts. First of all, I am still waiting on the breakout boards I made and ordered for the CC1101 Wireless modules. I figured out how SPI works on the C2000 and got it running on SYS/BIOS talking with my Aardvark SPI/I2C Monitor. Now all I need to do (once I receive my breakout boards) is get those wireless modules working! I have been reading the datasheet and I have a rough idea of what I need to do so we will see how it goes.

Major Addition:
I was talking to my dad about this project and he came up with a great idea! He suggested that I add a proximity sensor on the car to avoid collisions. I thought that was a great idea and found this SHARP IR Proximity Sensor. Basically it is an IR emitter and detector coupled in one package that spits out analog voltage between 0-5 V. I will pass that analog output through a voltage divider network to make sure it doesn't exceed 3.3 V going into the ADC of the C2000 Launchpad. So I will place this sensor on the nose of the car where the front bumper is and it will automatically brake the rear wheels if it senses an obstacle that is less than 5~7 inches away. Here is a picture of the sensor:

Sharp IR Sensor capable of sensing obstacles up to 80 cm away.

With the fast motor I am eventually planning on putting on the car, it is a good idea to have this sensor to "preserve" the car. I am really excited about this and I have already compensated for the sensor connections on the main circuit board that I shared above. Thanks for reading and please let me know what you think!

Edit: I just noticed the 3-D renderings differ slightly from the OSHPark renderings. The OSHPark renderings depict the most recent state of the circuit.

Motor Controller Design Update

So, it took me much less than anticipated to figure out how Eagle works. I was thinking it would take me the whole summer, but it only took 2 days. I downloaded the free version from their website and got cracking right away. I found an awesome tutorial on Youtube that walked me through the basics, and then I got the hang of it.

I did a little research on how I can actually get the PCB manufactured, and it turns out it is not so cheap. As you would expect, the price goes up as the board gets larger. Therefore, I tried to keep my design as minimal as possible. My original plan was to have the "big" MOSFETs (I explained what I meant by big in my last post) laid horizontally so I can use some large copper plates on the board as heat sinks. The MOSFETs I am using come in TO-220 packaging which means you can mount them to heatsinks since they come with a big area of expose metal in the back. Here is a picture of TO-220 packaging (source: Wikipedia).

However, I had to ditch that idea because the boards became too big for me to be able to afford. I am going to use oshpark.com's service to get the board manufactured and they charge $5 per square inch for a 2-layer board. However, they do give you three copies of your board for that price. Anyways, here is a screenshot from Eagle of how the PCB currently looks like. 

I actually really like oshpark's website. It looks really simple and it is very easy to use. To get a quick quote and to get your design verified, all you have to do is upload your Eagle PCB design files. Then they automatically process it online and give pictures of how your board is going to look like when it is printed. My board is going to be 2-layers, and its dimensions are 3.44x1.5 inches. This is going to cost me a tad over $25 for 3 copies. Check out the OSH Park renderings below. 

Board Top

Board Bottom

Top Layer

Bottom Layer

You might spot weird connections on the board. This is only my first time, and it turns out routing wires on 2-layer boards is very tricky. This is probably the design that is going to be manufactured. I go back to the design files every once in a while and try to spot any mistakes. But because the transistors will be vertical rather than horizontal, there won't be any heatsinks on them. This means that I can't pull more than a couple of Amps continuously (hopefully). Trying to pull more than that will cause the transistors to overheat.

Let me know what you guys think!

Anil

Update on the RC Car

Hey all,

Don't think that I gave up on the RC car project. I have been extremely busy with school, but I have also been doing my research. Here are the updates, firstly, I ditched the Bluetooth idea for the car. Instead I am going to use a 433 MHz RF transceiver. This will give me a range of at least 500 ft hopefully.

I am also currently in the market for a higher RPM motor. For initial testing, I will stick with the motor that came with the car. Good news is that I am building my own motor controller!

Here is the background info: you can't just drive a motor directly off of a pin on your microcontroller, you will literally blow up that MC if you try that. DC motors require a lot of current, especially when they stall. And for that, you need beefy transistors. In my design I have 8 transistors. 2 of them are p channel MOSFET s and the rest are all n channel MOSFETs. The 2 of the 6 NFETs are what I call "big" which means the motor current runs through them. Similarly, the PFETs are also "big" since they are directly interfaced with the motor. The other 4 "small" NFETs are used to drive the big MOSFETs.

The design is attached to this article. You basically don't want the wrong combination of MOSFETs on simultaneously since you will short your power source. To make sure this never happens, I am adding a logic protection layer. The logic circuitry has one 2-4 decoder, 1 NAND gate and one inverter. I have the logic on the design schematic. Basically, as far as the MCU is concerned, there will only be two wires between the MCU and the motor controller. 0-0 means neutral motor, 1-0 means forwards, 0-1 means backwards and finally 1-1 means motor brake. Motor braking is achieved by shorting the terminals of the motor.

Anyways, I am currently waiting on the last part, which is the decoder. I currently have the circuit partially wired up for testing. I am also attaching a picture of it. I was able to run my motor in both directions successfully. Once I have all the parts and finish testing, I will start to learn how to use Eagle. I want to make a PCB with this circuit on it. Once that is done, this baby will go on the car!

You might ask, why build your own motor controller? Because theoretically, I can pull nearly 20 AMPs (if I had heatsinks) from this circuit and the generic motor controllers out there only provide 1 A continuous current. I am making this car OVERKILL!!! Which means I want 25 million amps of current!

But no, realistically, I am shooting for about 2 amps of current, given that I find a battery that is comfortable with that. Anyways, hope you enjoyed the update.

Anil

Project IP - MSP430 Powered Remote Controlled Car!

Hey All,

I know I haven't been around for a very long time. School did its best to keep me busy and away from the microcontroller world this semester. However, the semester is almost over and I have already started thinking about what kind of projects I will want to work on over the break and presumably next semester before classes start getting difficult again.

Also, I have added a new project on the blog. Well, I say new, but it is actually something I did all the way back in April 2012. I just had a chance to share it. It is called the Multifunctional Bluetooth Temperature Probe. Yeah, yeah, I know it has a cheesy name, but that was the best I could come up with. Still though, you should check it out! You should also watch the video of me explaining how the system works. That is also pretty cheesy, so you might get a laugh or two out of it. Don't blame me, I am not good in front of the camera, I get excited.

Now to the topic, NEW PROJECTS! I have two projects that have been keeping my brain busy past few days!

• MSP430 Powered Remote Controlled Car!

I have already started gathering the parts I will need for this project! First of all, I need an RC car. You might ask, why are you buying an RC car to build an RC car? Well, the answer is my brains only works for electrical stuff, not much for mechanical. An RC car has all the gears and other small parts needed to turn and spin the wheels. That is the kind of stuff I wouldn't be able to take care of on my own. The reason why I want to this project is that I have never worked on a "robotics" project before. And this project involves a sort of motor controlling application, so I figured I would challenge myself!

Better yet, I might even upgrade the motor that will come with the RC car. I had one big criteria for the RC car when I was online looking for it, I wanted the biggest RC car that I could find (and I could afford). I figured it would be pointless to buy a fully functioning RC car and then "turning it into" another RC car. So I went on eBay and found this gem at this link. It is 1/10 Scale Ferrari Modena RC Car. Better yet, the mechanics are intact and it even comes with a battery!

Picture of the donor RC Car

In short, here is the plan with this project. Once I get all the parts I need, I will take all of the electronics out of the Ferrari and replace them with my own. The brain will be an MSP430G2553 (most likely) and it will control two motors. One is the main motor that drives the rear wheels, the other is a servo which will control the front wheels. I will also have to build a remote control for this guy, for which I will use an old X-Box controller. The driver will have full control over throttle and steering, which means that the speed of the car will be fully controllable (between 0%-100%). Same goes for steering, wheels will not only fully lock into one direction but will be able to turn to any degree in between (this is where the servo comes in). 

Before I end this post, I just want to say that I have many crazy ideas running through my head. I am thinking about making this system as complicated as possible. For example, I am thinking about adding an LCD screen to the controller which will show me the state of charge on the car, how much current the motors are pulling and how many volts the battery measures...

The Graphical LCD screen mentioned above.

One last note, which may come to you as a surprise, the wireless communication will be via Bluetooth. Yes I know you didn't expect me to choose Bluetooth, it is not like I ever prefer Bluetooth in my projects (sarcasm). But do visit the blog regularly, I am in the process of collecting the materials and once I have them all, I will build this!

Thanks guys,

-Anil

Update: I just won the auction on eBay for that Ferrari RC car!