ithanium2
Posts: 7
Joined: Thu Apr 05, 2018 6:37 am

4WD RC Robot

Thu Apr 05, 2018 7:01 am

Hello,
I am a college student and a newbie in electronics/robotics&co. but I am very eager to learn.

!!!DISCLAIMER!!! - I might say some stupid things, try not to laugh that hard and help me :)

I am attempting to build a semi-autonomous 4WD robot. Most of the plans and parts are somewhat sorted but I am kinda stuck :)

Chasis: Dagu Wild Thumper 4WD
Motors: 4 x Pololu 75:1 Metal Gearmotor 25Dx54L mm HP 6V
7.4V 5000MAh LiPo
FrSky RC controller with FS-I6B reciever
Raspberry Pi3 model B+
No clue what motor controller would be suitable.

For the robot control "requirements": robot could be configured to run autonomously most of the time, but a human operator could override the autonomous function if the robot gets stuck, and if possible transition back to autonomous mode.

I guess that to be able to achieve this, the Rpi, the motor controller and the RC reciever module are the key.

The reciever is this - https://hobbyking.com/en_us/turnigy-ia6 ... -sbus.html
It supports PWM, PPM, SBUS or IBUS protocols.

For motor control I was thinking about this shield - https://www.pololu.com/product/3751
The nice part about it is that I can power everything with one LiPo pack.
The confusing part is that it says it can control the motors only by PWM and it doesn't have current sensing. Also Operating voltage range is between 6.5 and 30V and my motors run at 6V.

Any help or advice is highly appreciated. Thank you!

ithanium2
Posts: 7
Joined: Thu Apr 05, 2018 6:37 am

Re: 4WD RC Robot

Sat Apr 07, 2018 12:27 pm

Anyone? :)

In the mean time I did more research and I am tempted to dump the shield approach.
If I understood correctly the Pi has some trouble controlling motors via PWM.

On most builds that I saw online (many of them do not include a Pi), people are using an Arduino to drive the motors.

So it got me thinking of 2 options:
1. The Dagu T'rex Motor controller - https://robosavvy.com/store/dagu-t-39-r ... oller.html
2. Pololu Trex DMC01 - https://www.pololu.com/product/777


Both of them will cost me the same, more or less, so the price is not an important factor.

LE:

A third option, and cheaper I guess would be to buy 2 BTS7960B 43A H Bridge Motor Drivers - https://www.banggood.com/Semiconductor- ... rehouse=CN

ithanium2
Posts: 7
Joined: Thu Apr 05, 2018 6:37 am

Re: 4WD RC Robot

Mon Jul 30, 2018 7:10 pm

Anyone?

I have made little progress on the project so far, but I have most of the parts:
- chassis, motors, lipo, RC TX/RX, the Raspberry Pi 3 and a Pololu Trex DMC01 motor controller.

So far I managed to RC control the robot just using RC and the motor controller, but ofcourse that is not enough....it's just an RC toy.

Alternatively, I managed to connect the RPI to the motor controller via serial TTL interface and I am able to move the robot forward or reverse.
My "master plan" has several steps and any help or advice is much appreciated:

1. For starters I want to be able to send RC commands to the Pi and control the motors based on those commands.


The grand plan is to be able to make a semi-autonomous robot that can avoid obstacles and map it's traveling route.
My plan may be abit ambitious...and possibly ambiguous :)

For obstacle avoidance I was thinking to use 4 Sparkfun HC-SR04 ultrasonic sensors.
For navigation I was thinking to use the Pololu MinIMU-9 v5 and a GPS module.
The GPS module...here's where things get interesting... I saw there are some GPS+GSM modules and that is great if I could use the GSM module for "heavy" data transfer. And here is the dilemma:
- the plan is to ditch the RC when the robot is operated by a human and use a smartphone app for that. Thing is that I want the Pi to receive commands form the phone, and send a video stream from a connected RPI camera to the phone. Is that possibile?

Will5455
Posts: 126
Joined: Sat Jul 21, 2018 8:37 pm
Location: harrisonville mo

Re: 4WD RC Robot

Mon Jul 30, 2018 7:18 pm

Technically it is possible over Bluetooth.
Never found a tutorial for it though.
I do strange things and am sometimes the techhead stereotype.
deal with it!

ithanium2
Posts: 7
Joined: Thu Apr 05, 2018 6:37 am

Re: 4WD RC Robot

Tue Jul 31, 2018 4:36 am

Nah, Bluetooth is not an option. "Worst" case I'll consider using WiFi.

ithanium2
Posts: 7
Joined: Thu Apr 05, 2018 6:37 am

Re: 4WD RC Robot

Thu Aug 09, 2018 4:27 pm

No one willing to offer some support? :(

I have decided to take "baby steps" approach on the project and I have made some progress.


So far, I have managed to control the robot with a smartphone via bluetooth. I am using the Bluedot app for smartphone to control the robot. For the moment (at least until my Pi camera arrives) I will tinker with it via a bluetooth and learn some principles on controlling the robot.

The next step, for now is adding 4 HC - SR04 ultrasonic sensors. I managed to setup one of the sensors and it seems to work properly. My issue is that I might not have enough GPIO pins to connect other sensors. Also, will the Pi provide enough power?

User avatar
Defiant
Posts: 181
Joined: Tue Oct 30, 2012 6:17 pm
Location: Hamburg, Germany

Re: 4WD RC Robot

Thu Aug 09, 2018 7:58 pm

As IMU try a Bosch BNO055 one, as its robust against magnetic interference and will help a lot for good odometry.

Disclaimer: Linking to my own project page here..
ithanium2 wrote:
Mon Jul 30, 2018 7:10 pm
- the plan is to ditch the RC when the robot is operated by a human and use a smartphone app for that. Thing is that I want the Pi to receive commands form the phone, and send a video stream from a connected RPI camera to the phone. Is that possibile?
Why should it be impossible? But why don't you use your smartphone in the first place?

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