I'm building an off road RC car. But in order to fully understand this story we have to go back, all the way back, to the beginning. This is how it all began:
Sparky is the first thing I ever built and designed myself.
It all started with a geared Tamiya motor attached to a battery, and it worked! The motor actually turned the wheel!
From there I made a car which started off as cardboard but quickly got upgraded to a wooden body. Then I added a motor and a propeller in the back to make it amphibious. I learned that to attach 2 turning rods together a universal flexible shaft coupling is needed because if you attach the motor directly to the shaft you will never align it perfectly, so the motor will waist energy in turning the misalignment. I also learned to oil motors if they get wet because if they rust inside it takes a lot of oil and luck to get them to work again. Dont worry Sparky is fine now.
Sparky was a lot of fun to build and now I was hooked on making a more off road car. I bought bigger back wheels but quickly realized that even though bigger wheels make cars more off road there is a lot more to it.
So, I built a car with more clearance, a lot more clearance.
I tried to implement the steering such that if only the left wheels turn it goes right and vise versa. But this did not work because waaaaaayyyyy too much friction.(note from the future: this would have worked if one pair of wheels was freely spinning but because I had motors on all 4 wheels even if all 4 were powered there was too much friction)
I also tried turning the front wheels backward and the back wheels forward when the car hit an obstacle to try to make the car drive onto the obstacle and flip over instead of just stopping but that did not work either.
After my failed steering attempts with 4 wheels I went to 2 wheels. I attached two forward-stop-reverse switches to a pair of 1.5v batteries and a vvvvveeeerrrrrryyyyy long cable to 2 motors(1 switch for each motor)
It works! Its very offroad if it has speed.
Turns very easily. To easily because only on or off no inbetween and car always drifts a tiny bit, so impossible to go in a straight line. But very fun to drive. (Also need pull relief for this design!!!)
Having such a long wire allows to build an RC car with a simple circuit instead of (foreshadowing) dealing with RC electronics. And it taught me to always always have pull relief(attach the wire in such a way that if you pull on one end the other end attached to the motor does not move despite the pulling. Or even better put a connector inbetween so it rips out of the connector and not out of the motor).
Also I did not include it in the picture but I later added another battery(so instead of 3v its 4.5v) because of all the loss over the long cable.
You remember the foreshadowing part? well this is the part of the story when I really leveled up the electronics.
But first we've got to talk about steering. I had never used a servo before so... Lets just say I did not know what I was doing. I glued the turning part of the servo directly to the turny part of the car, turns out servos are not that strong lol. But after a few more failed attempts, I eventually got the hang of it and learned that connecting the servo to the car with a paper clip(or other small bendy rod) did the trick.
Ok back to electronics. I first went with arduino because it's a cool toy but it's not really meant for remote controlling, so I got a controller and receiver instead(I mean you can do it but I did not have the right parts to do so and if I'm ordering stuff any way might as well buy a real remote control). The servo is really easy, just plug it into the receiver and power everything, tada. Motors not so easy. For both arduino and RC controllers you need an ESC(Electronic Speed Controller) because motors require more current then either of the two can provide.
(Side note on motor drivers/controllers: motor drivers are the more general term. ESCs are a specific type of motor controller commonly used in RC stuff and they have some electronics inside so they take PWM as input(to communicate with the receiver) as well as a power supply and then from that they generate a PWM signal to control the speed of the motor. Technically the input signal is not PWM for all models but PWM is the most common one. Most ESCs have BEC(Battery Eliminator Circuit) meaning they also power the receiver allowing to have one battery for everything, traditional motor drivers do not have this meaning the ESC and the receiver have separate power sources.
Basic motor drivers just have an external power source to power the motors and then a separate PWM as input which controls the switching rate of a H bridge to determine the speed. This is nice and simple but the issue is that this only works for brushed motors. For brushless motors you need to electronically commutat because there is no mechanical commutation mechanism. So the switching is more complicate and requires dynamically changing the PWM and might even need several different PWM signals depending on the setup. This is why ESCs have specialized electronics in them and dont just use the same PWM input to regulate the speed.
Here is a great article about ESCs if you want to learn more: https://www.tytorobotics.com/blogs/articles/what-is-an-esc-how-does-an-esc-work?srsltid=AfmBOoplkTxE2fCLkyyA-T7kQhOkJidEp9XpWyfOEhwXWWpEqcYnoaM-)
Back to Offroady. So far so good. Only problem is ESCs are quite sensitive. So it kindoff worked with nonrechargeable batteries but with rechargeable ones(since they provide slightly less current and voltage) nothing was moving. It turned out my 6v battery pack had too thin wires so not enough current could get to the ESC. So I replaced those with thicker wires and also soldered the wires onto the battery pack instead of just clamping(why are battery holder wires not soldered by default?).
Once the current :) problems resolved my first truly remote controlled car turned out to be the most off road vehicle yet. It has steering and can go over a few books if it has enough speed and the book pile is not to steep.
After the success of offroady, I made some designs without steering and using the same electronics to test what mechanical improvements I could make to make offroady even more off road.
Having the front wheels aligned with the back wheels gives the front wheels more support/strength making the car more off road.
I brought Triangular back to life and installed the electronics from offroady. And as before the car does not scrape but does not get over obstacles. Also, if it hits an obstacle that is to big it will vibrate a little bit while if the offroady design without steering and aligned front-back wheels hits the same obstacles it also does not go over it but it just does not move/no vibration.
Probably because for triangular since body is not straight the force from the motor is not directed forward but up along the triangular body. So the car has less power since forces are in the wrong direction.
Even though 4 wheeled Offroady was a big success I was still convinced that RC car cable car was so hard to steer not because its only 2 wheels but rather because I could not control the speed. So I built Biky which is just like RC car cable car but without the cable(ok and a few other changes).
Remember the foreshadowing? If you thought the ESC for offroady was annoying, well it gets worth. Initially I used the same electronics as for Offroady just that I used 2 ESCs instead of 1 since Biky has 2 motors which need to be able to operate independently. However, if you disconnect the power wire of all except one of the connections between ESC and receiver then you can work with only one battery pack(the specific ESCs that I was using were directly connected to the battery and were powering the receiver and everything else).
It worked great when I tested just the electronics but then before assembling everything into the chassis I decided to use different motors.
ESCs are motor specific. But I did not know that so it did not work.
I used different motors then for offroady because Biky has only 2 wheels, so balance is much more important and space much more limited. But unlike RC car cable car I wanted geared motors because I thought if it goes slower but has more power it would be more offroad.
This however, required a different type of ESC which I learned the hard way. But it's ok I ordered some new ones which conveniently where way smaller than the previous ones. They also did not power the receiver, so I did not have to do any power cable removing. To choose the correct ESC I mainly focused on current ratings because the small geared motors I am using are more efficient/need less current than the motors I used before.
Once I figured out the ESC stuff it was time for a test drive.
Just like RC car cable car it is impossible to go straight. It's not about controlling the speed its just that 2 wheels are inherently unstable, thats why its so easy(to easy) to turn.
I found that the cable from RC car cable car actually helped with steering because the car tugged on the cable a bit which introduced friction. Biky felt harder to drive so it's hard to say how offroad it is.
Both mecanum wheels and Omniwheels can make a car drive sideways(aka go 90deg to its orientation without changing orientation) but they are not exactly the same. They both have rollers to do the sideways movement but the mecanum wheels have these rollers angled while the Omniwheels do not.
These wheels look really cool, so I bought 4 mecanum ones to see if they would live up to the hype. Spoiler alert they do.
Wikipedia has a nice drawing explaining how the wheels have to turn to go in the wanted direction.
https://en.wikipedia.org/wiki/File:Mecanum_wheel_control_principle.svg
I also tried arranging the wheels in different ways to see how the orientation of the rollers affects the car. I tried 4 different patterns:
\ / \ / / \ \ \
/ \ \ / \ / / /
and for all of them going forward and backward is the same remote control input.
The X shape is the only one which allows pure sideways motion which is really cool and satisfying to watch.
I had the issue that one wheel would sometimes not turn even though the remote control was telling it to move but since this affected all wheels at random I think this is an ESC issue. I did not have enough ESCs that are like the ones I used for offroady and I could not find the exact same ones, so I had to buy slightly different ones.
Otherwise in terms of offroadness its about as offroad as offroady which was a pleasant surprise.
So far I limited myself to wheels because I thought they are so much faster than tracks. But many super off road vehicles have tracks because wheels have the disadvantage that they can only overcome obstacles that are less then half their diameter in height(assuming no run up). So I have to at least give caterpillar tracks a try. I did some googling and landed on 3 main designs:
But then I remembered that many years ago I got this cute little tracked robot toy which has tracks attacked to the tracks allowing it to pull itself up over pretty much any obstacle no matter how big. Plus it uses only a single battery! The only thing is that this robot has no steering. So If I add steering to this design it could be the most offroad vehicle I have built so far by a long shot. The question is just if the second track will hinder the steering from working properly.
I played around with my little robot and discovered that if I put just the right amount of weight on it, it wont go up and down on flat terrain but it is still light enough so that it will go up if it meets an obstacle.
After Thinking about where to get parts, I realized that the easiest way to build this would be out of lego.
Building it was rather easy, however for this first design I did not attach a motor because I didnt quite know yet how to build an adapter for my normal 3v-6v motors or if I should buy a lego motor.
Turning the gears by hand: Differential steering works! It's a little awkward because it goes up and down as it moves but it works. Also, I discovered that the ratio between the big and the small track is super important. The longer the small one the higher it can go meaning more off road but it's much harder on the gears. The smaller the small track the easier it is to move as the robot has to lift itself up less.
I had the idea of adding motors by connecting the shafts with rubber tubes which worked quite well. The rest of the electronics and wiring is identical to Biky. However, crawly did not crawl well at all. After changing the gear ratio such that the motor rod ends in a small gear connected to a big gear, it worked great going forward. But backwards did not work at all(not enough strength since the lever arm is much shorter in that direction) and when going over obstacles crawly would topple over backwards. I was able to fix the toppling over by moving the battery pack all the way to the front. Then I had the idea of lowering the back by one lego technic block and this enabled going backwards if the battery was in the center(in this position it topples over when going over obstacles but at least it can do proper differential steering since it can go backwards.) I tried adding another technic block but that made it worth again so I guess 1 lower is ideal. By the way crawly goes up and down even on flat ground, finding the right balance point is really difficult.
I then also tried having one of the small tracks in the front and the other in the back to see if that makes a difference. I right away attached the opposite side of the small tracks lower so that backwards would be easier. Surprisingly, it's better because as long as the battery is in the front, crawly can both go backwards and go over obstacles without falling over. If the obstacle is very big it still topples over because its center of mass is too high but it at least attempts it which is impressive. For turning you have to go forward and backwards a bit because it's easier for crawly to lift itself up onto its small tracks when both small tracks are trying to lift. This results in the turning radius being quite big but otherwise it turns great. However, this configuration is harder on the gears, so I made the gear that is connected directly to the track bigger. In this configuration crawly also does not go up and down on flat ground.
(Also I might need to add a fuse box or something because im pretty sure I partially burnt one of the motors since it does not always turn properly anymore.)
It's definitely a bit of a wobbly construction but Crawly is much more off road than anything I have ever built.
Now I technically achieved my goal but I want to try one more thing before I end this article. There are many more car designs I could make, what if I had front and back wheel steering(it would be hard to drive through, but really cool) or add a mechanism so it can jump over obstacles or out of holes, or...
I could go on and on but one thing that sticks out is that I managed to do an entire article about off road cars without talking about 4 wheel drive! So, to finish it off(for now) I want to build another RC car which will have shock absorbers and is similar to Offroady but 4 wheel drive. Note to self: put a servo saver(absorbs shocks so the servo does not break in a crash).
Coming soon
Copyright © started building in 2017, article written 2023-2026 Jessica Socher ()
