For a long time I have want­ed to build a remote con­trolled robot car capa­ble of being con­trolled via the Inter­net, at long ranges using 4G/LTE cel­lu­lar con­nec­tiv­i­ty. So I did.



I used a Rasp­ber­ry Pi 3B+, an Adafruit DC and Step­per Motor Hat, and a Log­itech C930e USB UVC web­cam.



Build­ing the robot

Chas­sis with four motors

Chas­sis with four motors and top sec­tion attached

Com­plet­ed robot

Com­plet­ed robot

The robot is capa­ble of con­nect­ing to the Inter­net using Wi-Fi. I was able to slight­ly increase the effec­tive Wi-Fi range by using a Mikrotik router and alter­ing the hard­ware retries set­ting and frame life set­tings. The inten­tion was to quick­ly recov­er from trans­mis­sion errors and avoid con­ges­tion. This dis­card­ed video pack­ets that could not be deliv­ered in real time, and kept the net­work clear for when trans­mis­sion would be suc­cess­ful. I also used ipt­a­bles and man­gle to alter the DSCP of the live video stream pack­ets with the same inten­tion.

To enable a long range con­nec­tion, I used Twilio Pro­gram­ma­ble Wire­less to con­nect to local 4G/LTE cel­lu­lar net­works. I sub­stan­tial­ly low­ered the data rate to around 250 Kbps to make trans­mis­sion more reli­able and reduce costs, and was able to get a vir­tu­al­ly flaw­less live feed.

Twilio Wire­less Inter­net of Things Starter Pack

Mon­i­tor­ing 4G/LTE data usage with Twilio Pro­gram­ma­ble Wire­less

The live video and audio stream uses FFMPEG for com­pres­sion and stream­ing, and has a pletho­ra of set­tings to tune. I took the time to tune bitrate, buffer­ing, keyframe inter­val. I also ensured the web cam­era was able to native­ly encode video with UVC at the select­ed res­o­lu­tion to reduce the load on the Rasp­ber­ry Pi’s CPU. Video laten­cy was often under a sec­ond, which is impres­sive espe­cial­ly con­sid­er­ing the round trip involved.

Robot remote­ly con­trolled via the inter­net



The con­trol sys­tem uses Let’s Robot (now Remo.tv), based at Cir­cuit Launch in Cal­i­for­nia, which has a com­mu­ni­ty of robot builders who love to cre­ate and share their devices. The pro­gram­ming lan­guage of choice is Python, and I also linked to an exist­ing API I had cre­at­ed in JavaScript with Node and PM2.

Mission 1

Mis­sion 1 — 30 minute Night Voy­age

The first 4G/LTE long range mis­sion was suc­cess­ful, and the web­cam was good enough to be used at night. Dif­fer­ent mem­bers of the com­mu­ni­ty took turns to dri­ve the robot. It didn’t always dri­ve straight, so we had to dri­ve for­ward and turn to the left at reg­u­lar inter­vals. The robot drove for around 30 min­utes, and then got stuck when it fell down a side­walk. I had to quick­ly dri­ve to retrieve it =)

Mission 2

Mis­sion 2 — Involved Dra­ma

The sec­ond mis­sion was intend­ed to dri­ve from my loca­tion to a friend work­ing at a local busi­ness. How­ev­er half way through the mis­sion, a sus­pi­cious mem­ber of the pub­lic grabbed the robot, threw it in a trash can, and called the police. I wait­ed for the police and calm­ly explained that the robot was an edu­ca­tion­al project in telep­res­ence, and also told the per­son report­ing the robot that there were no hard feel­ings, despite inter­fer­ing and dam­ag­ing my per­son­al prop­er­ty.

Police!

Mission 3

As part of the com­mu­ni­ty site, it is com­mon to leave your robot open to be con­trolled. While unat­tend­ed, a sneaky indi­vid­ual drove my robot into a void of the house and man­aged to get it cov­ered in spi­der webs and oth­er filth, as you can see below. Thanks.

Cov­ered in cob­webs

Very dirty

I found that cats were very curi­ous about the robot invad­ing their ter­ri­to­ry, as you can see below:

A curi­ous cat inves­ti­gates the robot

I was very pleased with how the project worked, and had the oppor­tu­ni­ty to use Python, Node, and fine-tune wire­less net­work­ing and live video stream­ing, and of course remote­ly con­trol the robot as I had want­ed to do for a long time.

If you want to build your own robot, the guide to ‘build­ing a Bot­ting­ton’ is a great place to start.

Update: Twilio saw this post and gave me a $20.00 cred­it. Thank you 😁