Motor Requirements for an RC Power Functions car

[pjf1000]

I'm designing an RC technic car (C8 Corvette) in Stud.io that I want to race against some other people. How many L-motors will I need to get the car up to a reasonable speed? (I'd like it to go around 5-10 mph, basically anything faster than a slow crawl).  I have 2 L-motors built into the car right now, but I have a feeling they won't be powerful enough. I'm planning on using a BuWizz battery pack for power and bluetooth control. The car has around 1200 parts, so it probably weighs 3 pounds or so. I built a four speed sequential transmission into the car as well.

For a car of this weight, should I use 4 L-motors?

[msk6003]

Remove transmission.

If you want race with your model and not for showing, transmission is useless.

[SamuelYsc]

Check this size limit. I guess you are talking about the 42093 Chevrolet Corvette.
I have seen a few designs that are best with 2L and 1Servo and 1Buwizz. These setups are running quite fast at the video they show.

Here are some references I found.

Design by RacingBrick. 2L+1Servo+1Buwizz.

Upload by Buwizz, 1M+1Servo+1Buwizz.

 

If you want the Ultimate speed, I will suggest you to have two Lego buggy motors 5292. I have not seen anyone done that before. It will be quite challenging.

[amorti]

This model will give you an idea of how quick 4*L motors can go in a 1200 piece shell with a buwizz.

It uses the drive module from Madoca Icarus, which seems a great way to get the power of 4* motors to the wheels without skipping or stripping gear teeth. He says he had to use the new CV joints to get the power down. 

Next question is where are you racing? Assuming outside, suspension will be the next limiting factor.  If it's too stiff your car will bounce around and shake itself to death. Make sure you have some ground clearance too.

Edited May 11, 2020 by amorti

[kbalage]

My Corvette ZR1 mod linked by @SamuelYsc has 2 L motors, a Servo and a BuWizz unit and the weight is 700g. I did not measure the top speed but it should be around 10 km/h, it feels fast because it's pretty small. 

To reach a similar or higher speed with a bigger build you definitely have to use RC buggy motors, and for an optimal performance I'd say 2 buggy motors with 2 BuWizz units. No gearbox, minimal transmission, build should be as light as possible. This is my 42077 mod with this setup, the weight is ~1,3kg, top speed is around 13 km/h.

 

[Ashfall]

Your best Option is one or two buggy motors paired with an original battery box (The Race Buggy Battery) and the Original Remote Control (You will also need an antenna lol) I recommend you do motor-to-wheel output to reduce friction and make it go as fast as possible. Hope you win the race! :)

 

Race Buggy Battery

The Remote Control

 

Buggy Motor

[kbalage]

4 hours ago, Ashfall said:

Your best Option is one or two buggy motors paired with an original battery box

Not necessarily the best option, since it occupies more space, it is heavier and provides less voltage than 2 BuWizz units. Definitely cheaper tho :) 

[Ashfall]

@kbalage Yeah. I mainly meant the best option for speed. Idk how big his car is, so idk what setup would be best lol. 

[pjf1000]

On 5/11/2020 at 1:51 AM, amorti said:

This model will give you an idea of how quick 4*L motors can go in a 1200 piece shell with a buwizz.

It uses the drive module from Madoca Icarus, which seems a great way to get the power of 4* motors to the wheels without skipping or stripping gear teeth. He says he had to use the new CV joints to get the power down. 

Next question is where are you racing? Assuming outside, suspension will be the next limiting factor.  If it's too stiff your car will bounce around and shake itself to death. Make sure you have some ground clearance too.

Yeah, after talking with some other people, my 4 gear transmission seems unnecessary. I'll use that space to put in 2 additional L-motors. The car also has a built-in suspension very similar to the Mantis you mentioned.

Does a second buwizz provide additional speed, or just runtime? Not sure if I can justify buying a second one lol.

I attached a picture of the car; it's not finished but that's more or less what it will look like. It's about fifteen inches long.

It looks like the picture didn't upload... Here it is again:

[kbalage]

1 minute ago, pjf1000 said:

Does a second buwizz provide additional speed, or just runtime? Not sure if I can justify buying a second one lol.

With 4 L motors it definitely makes a difference, especially in high/ludicrous mode. With a single BuWizz unit you might have the protection kicking in in those modes, depending on the load on the motors (gearing, drive train complexity, terrain etc.).

Btw you can also try a more unorthodox way (you already tried BuWizz :D), using an SBrick and Rc LiPo batteries :) 

[2GodBDGlory]

My favorite setup for high performance (Since I don't have any RC buggy motors) is to build an absolutely tiny car, usually with 3.0cm diameter wheels, and then put in two L-motors geared up five times (Usually 24-8-24 hard coupling, followed by 20:16 bevel gears)

It is fairly low power, but the very low weight keeps it fast.