RC Car with in-wheel brushless motors

[janssnet]

Finally finished a first version of a LEGO RC Car with 2 in-wheel, brushless motors. While I know some of you hate the combination of RC electronics and LEGO, others enjoy these hybrid models (hence this post). 

If you are more the purist type and in favour of LEGO only, please skip this. 

If you like stretching the envelope using (RC) electronics please have look and let me hear your thoughts.

 

While searching for brushless in-wheel motors I ran into the ideal product: Turnigy Multistar 4225-610Kv. It mounts easily onto LEGO (same measurements) and fits almost any 56-rim. The result is spectacular. Great speed, no wear-out, all traction goes to the wheels, no gears necessary. Sadly, it turns out this motor is no longer available  (working on an alternative).

Car also includes an (adjustable) software differential running on an Arduino Nano, works surprisingly well. When fully applied the car has serious oversteer, when turned to 0 the car has understeer.

The body of the car is a 54100 modified boat hull  . It took some cutting but ended up nicely.

Please have a look at the video here: 

 

Edited July 25, 2022 by janssnet

[iLego]

Wow, that is some serious speed! I find such hybrid creations really cool. Thanks for posting and sharing. It will be nice if you can provide some more details of the model for the rest of us who have no clue how to do such things.

[janssnet]

Thanks for your reply. Building these models is not too difficult.

1. Build your LEGO car

2. Mount your (non-LEGO) motors  (this is the tricky part, happy to explain in further detail)

3. Put your RC electronics in (ESC's, servos (Geekservos are great), RC receiver, battery)

4. GO!!

Clearly it's not as sequential as described. The chassis should have provision for the electronic to make it work and look good, but these are the basics steps. 

Here is a link to the instruction PDF of the LBOW iWD2: https://drive.google.com/file/d/1lWDDGeADSEPiHKbdlmpJBG0MDvsfXlLK/view?usp=sharing

[gyenesvi]

Interesting stuff, I have been eyeing that Geekservo for a while, would love to test it in a build, but don't have the rest of the electronics (and the experience) to run it. I wonder why Lego servo seems far inferior to it in precision. Is it the ESC that does the trick of precise control (which the Lego system does not have)?

[janssnet]

On 7/23/2022 at 1:55 PM, gyenesvi said:

I wonder why Lego servo seems far inferior to it in precision. Is it the ESC that does the trick of precise control (which the Lego system does not have)?

There is indeed a significant difference in precision.The LEGO servo offers 15 positions. The Geekservo in this car has a 'dead band' of 4µs, which means, when using the 'normal' PWM pulse range of 1000ms - 2000ms, there are 250 positions.

The ESC has no role in this. The ESC drives the motor, not the servos. Servos are directly connected to the RC Receiver.

Why the resolution of the LEGO Servo is limited, I do not know. But I'm sure others have a perfect explanation for this .....

Edited July 25, 2022 by janssnet

[gyenesvi]

11 minutes ago, janssnet said:

There is indeed a significant difference in precision.The LEGO servo offers 15 positions. The Geekservo in this car has a 'dead band' of 4µs, which means, when using the 'normal' PWM pulse range of 1000ms - 2000ms, there are 250 positions.

The Lego PU servos (L motor) have more positions than 15 (theoretically I think at least 256, but maybe even 360), but still they seem to be much inferior in terms of controllability, even though the resolution seems comparable. They have a lot of lag and can only arrive to a given position after a number of steps.

11 minutes ago, janssnet said:

The ESC has no role in this. The ESC drives the motor, not the servos. Servos are directly connected to the RC Receiver.

That's interesting to know, thanks. Does the RC receiver have some sort of control unit in it that the Lego IR unit or a BuWizz does not have? I wonder why the Geekservo is not compatible with Lego wires / connectors, and I suspected it has to do with extra wires required for control signals. Is that the case?

 

[janssnet]

1 hour ago, gyenesvi said:

Does the RC receiver have some sort of control unit in it that the Lego IR unit or a BuWizz does not have? I wonder why the Geekservo is not compatible with Lego wires / connectors, and I suspected it has to do with extra wires required for control signals. Is that the case?

 

The protocol Lego and/or BuWizz is using to steer motors, I do not know.

What I do know is that Lego is often used in robotic and educational environments for prototyping. In these situations PWM (Pulse Width Modulation) is widely used as the preferred protocol to control servos and motors (Arduino for instance has standard libraries for this - Servo.h). And that is the market Geekservo is targeting (I assume), offering a Lego-brick compatible servo that understands a standard (50 Hz) PWM signal. Perfect for rapid prototyping.

The great thing is that (most) standard RC electronics also support this 50Hz PWM signal. The RC receiver converts a 2.4GHz radio signal into a PWM signal which is understood by (most) ESC's and servos. No need to stay within IR or Bluetooth distance anymore  and tons of new possibilities. 

The wiring of a (Geek-) servo: 1: GND, 2: +5-6V 3: Pulse (this is the PWM signal)