Help. Goal to build a 50mph lego RC car

[spazmanian]

Ok everyone I need some ideas /help and am also new to the forum. I am looking to build a 50 mph LEGO (strictly) RC Car. I was able to buy the LEGO RC Supersonic #8366 here in the US on Ebay as a starter mainly because it is truly built of Technic Lego's and is truly RC and NOT IR. I am now needing some ideas on building something that will go 50mph. If you have some good ideas and it doesn't get terribly expensive please give me some ideas. Thanks. Please keep in mind that I am in the US.

[Blakbird]

Ok everyone I need some ideas /help and am also new to the forum. I am looking to build a 50 mph LEGO (strictly) RC Car. I was able to buy the LEGO RC Supersonic #8366 here in the US on Ebay as a starter mainly because it is truly built of Technic Lego's and is truly RC and NOT IR. I am now needing some ideas on building something that will go 50mph. If you have some good ideas and it doesn't get terribly expensive please give me some ideas. Thanks. Please keep in mind that I am in the US.

I'm into both R/C and LEGO Technic. I have some R/C cars that will go 50mph and I can say without reservation that you will never achieve this with LEGO. The parts are just not made for it. You need very high speed/torque motors, ball bearings, tight fits, balanced wheels, and steel drive shafts to go that speed. LEGO loose fits on axles, plastic axles, and unbalanced wheels would destroy themselves even if you could turn them that fast.

Cool idea though. Perhaps you should concentrate on building a LEGO R/C model that just functions well at all before jumping to the high speed arena. Perhaps you will come up with some ideas to improve the speed in the process.

[Milan]

As Blakbird said, LEGO is just not built for that...probably you can achieve some nice speed, but 50 mph (equals 80 kmh), is too much I think.

You could put few powerful LEGO motors, gear them up, and connect them directly to the axle, but the wheels will rotate itself off the axle, I have seen this on some Zorko's dragsters powered by the LPE.

[DLuders]

Nevertheless, making a Lego Dragster could be a fun project. Check out Nico71240's "Dragster 2" video: http://www.youtube.com/user/Aremzi#p/a/f/0/pUCV3vwjF0s . He also has a video on "How to Combine 2 Motors" for a Lego Dragster: http://www.youtube.com/user/nico71240#p/u/41/Yn-T81PhwLU . You may get some ideas from them.

Be sure to visit his Brickshelf folder too: http://www.brickshelf.com/cgi-bin/gallery.cgi?f=339209 .

[TechnicJuan]

Impossible using 100% Lego.

[Zerobricks]

You can go 20 kmh max with lego RC (thats how fast my tricycle went).

[shimon]

um

maybe you can achieve that speed with a pneumatic engine like LPE

then you need just a good connection good chassis and a long long wire

[allanp]

That is a hughly difficult challenge, I think Blackbird is most qualified to answer this one so I would go with his answer but it would be interesting to see how fast a 100% technic vehicle could go. If you want to be completely pure then I would go for LOTS of RC buggy motors with one battery pack per two motors. The it's a mountain of trial and error to find out if you should gear up and how much by. Be very careful of breaking gears and wearing the plastic. If built pretty fast cars when I was younger and before I knew it I ruined gears, axles, beams, and so on. but if you don't mind using modified parts then you could go for the LPE engines (although these do really require non lego equipment to run). Good luck with your challenge.

[Commodore Hornbricker]

I raced RC cars for years (mainly off road) but there are many expensive RC's that cant do 50 MPH with electric motors. There is no way to do this 100% Lego IMO. At minimum you'd need a stronger motor but even then without bearings or a power train strong enough to handle that much power you'd just end up twisting Lego axels (you'd have to start out really slow and very gradually build up speed). You'd also need stronger batteries and a speed control device. Also at that speed every little bump would cause your car to come apart all over the place. For those speeds you would have to glue the bricks together...just my two cents. I think you should just see how fast you can make your car go to begin with and then keep trying to break your own record. Best of luck. Let us know how you do.

Edited April 21, 2010 by Commodore Hornbricker

[DLuders]

So, if building a 100%-Lego, 50-MPH RC car is "impossible", there is an alternative. Instead of abandoning the project altogether, how about CONSIDERING using ALTERNATE MATERIALS like aluminum. The Lego "purists" may object, but isn't a LEGO-LIKE model better than no model at all? If you want to keep an open mind, check out http://inanimatereason.com/shop/ and http://www.bricklink.com/store.asp?p=InanimateReason (click on the "Custom Items" at the top-left corner of that website). Using aluminum liftarms, metal axles, RC wheels, and servo motors COULD allow a person to create a 50-MPH Lego-like RC car. Talk to Bill Shaw about it at toppsoft@gmail.com .

[spazmanian]

I'm into both R/C and LEGO Technic. I have some R/C cars that will go 50mph and I can say without reservation that you will never achieve this with LEGO. The parts are just not made for it. You need very high speed/torque motors, ball bearings, tight fits, balanced wheels, and steel drive shafts to go that speed. LEGO loose fits on axles, plastic axles, and unbalanced wheels would destroy themselves even if you could turn them that fast.

Cool idea though. Perhaps you should concentrate on building a LEGO R/C model that just functions well at all before jumping to the high speed arena. Perhaps you will come up with some ideas to improve the speed in the process.

I have already used the supersonic motors and such to power my Lego Nitro Muscle and it worked ok. But, it definitely was not a rocket per say.

um

maybe you can achieve that speed with a pneumatic engine like LPE

then you need just a good connection good chassis and a long long wire

LPE. I guess I have not seen that for Lego. I would be open to that idea to help build something quick.

Edited April 22, 2010 by spazmanian

[johanby]

Taking all solid mechanics issues aside, there is of course another problem. A wheel with 30 mm diameter would need to rotate with about 14000 rpms to achieve a speed of 80 km/h. A bigger wheel would of course need less, but still a wheel with 60 mm diameter would need to rotate with 7000 rpms. The XL motor would need an upgearing of about 32:1 and the race buggy motor would need an upgearing of about 5.4:1. Heck, even the high rev low torque 2838 motor would need an upgearing of about 1.7:1.

[DLuders]

LPE. I guess I have not seen that for Lego. I would be open to that idea to help build something quick.

LPE = Lego Pneumatic Engine: http://www.nicjasno.com/ .

[Raphy]

Well, how about setting your goal down to about 30-35 MPH? See if you can do that... then try for, say, forty. Then forty-five... and then fifty.

One step at a time, man! :D

If you're making a dragster, you know all the power in the back and hardly any up front, you almost certainly need to put a wheelie bar on the back. Otherwise, it'll simply flip somersaults.

(You could use perhaps, ten pull-back motors for one axle. That might do it. Try winding it up, though... ;P)

[Brickthus]

Ok everyone I need some ideas /help and am also new to the forum. I am looking to build a 50 mph LEGO (strictly) RC Car. I was able to buy the LEGO RC Supersonic #8366 here in the US on Ebay as a starter mainly because it is truly built of Technic Lego's and is truly RC and NOT IR. I am now needing some ideas on building something that will go 50mph. If you have some good ideas and it doesn't get terribly expensive please give me some ideas. Thanks. Please keep in mind that I am in the US.

Some key issues to make a LEGO car go as fast as possible:

- powerful motors

- minimal gearing

- big wheels

- light vehicle weight and power supply

The motors most suited to RC cars are the 5292 motors, which you have two of in set 8366.

Have you tried larger wheels with these? Perhaps the 82mm motorbike wheels and tyres?

This would get the most out of 2 motors and wheels without gearing.

The next step is to use larger wheels, but this would need more motors. Perhaps four 5292 motors could drive a pair of Hailfire Droid wheels with suitable light and strong construction to create a hub for them.

Other than that, you're not likely to get a higher power to weight ratio without using an RC Car motor and more battery power than LEGO systems provide.

An RC car might give 40 Amps from a NiCd pack for a single motor, but no LEGO motor is designed to handle more than 1.5A. The Power Functions XL motors are the "more powerful motors" that we've been asking TLG for for years, but LEGO parts will never get conventional Technic motors into RC territory because the medium can't handle the power. An XL motor can twist a short axle, so anything more needs metal axles, metal beams and proper bearings.

I recently melted a beam and axle having mounted a drill (see advice) in some bricks in order to drive a jet engine model faster than 3000rpm. This was intended to be an advance from using four 4000rpm 9V Technic motors with only their own bearings and no axles through beams, which had drawn about 1.3 Amps at 9V from a bench power supply. The same limits apply to flying as to going fast.

There is another way to achieve 50mph with a LEGO model, but only to fire it with a catapult!

Mark

[legoman777]

as people have said above, i think its impossible with only lego.

as people have said above, i think its impossible with only lego.

[spazmanian]

Very interesting. So maybe I will close this one out and start a new one stating a goal for 30 MPH and the will to use items from Inanimate Reason if need be? I just want something to prove by end of summer :> :.

Some key issues to make a LEGO car go as fast as possible:

- powerful motors

- minimal gearing

- big wheels

- light vehicle weight and power supply

The motors most suited to RC cars are the 5292 motors, which you have two of in set 8366.

Have you tried larger wheels with these? Perhaps the 82mm motorbike wheels and tyres?

This would get the most out of 2 motors and wheels without gearing.

The next step is to use larger wheels, but this would need more motors. Perhaps four 5292 motors could drive a pair of Hailfire Droid wheels with suitable light and strong construction to create a hub for them.

Other than that, you're not likely to get a higher power to weight ratio without using an RC Car motor and more battery power than LEGO systems provide.

An RC car might give 40 Amps from a NiCd pack for a single motor, but no LEGO motor is designed to handle more than 1.5A. The Power Functions XL motors are the "more powerful motors" that we've been asking TLG for for years, but LEGO parts will never get conventional Technic motors into RC territory because the medium can't handle the power. An XL motor can twist a short axle, so anything more needs metal axles, metal beams and proper bearings.

I recently melted a beam and axle having mounted a drill (see advice) in some bricks in order to drive a jet engine model faster than 3000rpm. This was intended to be an advance from using four 4000rpm 9V Technic motors with only their own bearings and no axles through beams, which had drawn about 1.3 Amps at 9V from a bench power supply. The same limits apply to flying as to going fast.

There is another way to achieve 50mph with a LEGO model, but only to fire it with a catapult!

Mark

So, if building a 100%-Lego, 50-MPH RC car is "impossible", there is an alternative. Instead of abandoning the project altogether, how about CONSIDERING using ALTERNATE MATERIALS like aluminum. The Lego "purists" may object, but isn't a LEGO-LIKE model better than no model at all? If you want to keep an open mind, check out http://inanimatereason.com/shop/ and http://www.bricklink.com/store.asp?p=InanimateReason (click on the "Custom Items" at the top-left corner of that website). Using aluminum liftarms, metal axles, RC wheels, and servo motors COULD allow a person to create a 50-MPH Lego-like RC car. Talk to Bill Shaw about it at toppsoft@gmail.com .

I am now very open to this and have emailed the inanimatereason.com website to see what they have to offer in this arena. I am willing to suffice at 30mph if need be :> :>

[Mark adler]

I am building a 50mph LEGO car currently!

6 buggy motors, 2 of the “indy car” bodies, with batteries, and steering modules, from the late 90s?

direct drive on both axles, and the large diameter mindstorm wheels/tires!

it is heavy, but when done, I will replace batteries with lithium AAs

it will have only a few degrees of steering!

anyone know how many rpm 4 buggy motors on one axle ( direct drive) will turn? What rpm do I need to reach 50 mph

yes I know due to torque, it will take about 100 feet to reach top speed!

the car will be about 2 lbs

[Jurss]

Only batteries will be non lego?

14 hours ago, Mark adler said:

and the large diameter mindstorm wheels/tires!

If not mistaken, they are some 9 studs diameter, motorcycle tyres will be some +4 larger, so less rpm will be needed.

 

14 hours ago, Mark adler said:

What rpm do I need to reach 50 mph

Do simple calculations, basic geometry.

[Zerobricks]

14 hours ago, Mark adler said:

I am building a 50mph LEGO car currently!

6 buggy motors, 2 of the “indy car” bodies, with batteries, and steering modules, from the late 90s?

direct drive on both axles, and the large diameter mindstorm wheels/tires!

it is heavy, but when done, I will replace batteries with lithium AAs

it will have only a few degrees of steering!

anyone know how many rpm 4 buggy motors on one axle ( direct drive) will turn? What rpm do I need to reach 50 mph

yes I know due to torque, it will take about 100 feet to reach top speed!

the car will be about 2 lbs

No to be rude, but if you haven't yet calculated theoretical top speed from motor RPM and wheel diameter, than you are not ready. As someone who managed to push a 3,6 kg Lego car to almost 30 km/h I can tell you reaching 50 mph (80 km/h) will be VERY HARD and you will need to do a lot of calculations regarding gear ratios, torque and even air resistance forces which will be encountered at such speeds.

[Technic Builder]

If you remove both stages of gear reduction from PF XL motors I think you increase the shaft speed by either 25x or 36x.  If you were to build a very long car with a series of XL motors directly driving larger wheels (like maybe the smoother motorcycle wheels / tires) it may be possible.  Basically the vehicle needs to produce enough power to overcome the aerodynamic drag forces at 50 MPH.  Because the power / weight ratio of the motors is quite low you'll have to have a lot of motors and battery packs in a very long slender vehicle.  The vehicle would also probably need at least 1/4 mile to accelerate, maybe more.
 

Now, taking out gear reduction from the XL motors is already cheating, but if you're willing to do that, you could also connect two battery packs each with NiMH batteries in them together to get 14.4 volts and run the motors on that.  I believe lego motors are 12v motors that are run on 9v for safety and longevity.  Increasing the motor voltage greatly increases their power output.

But I would still say with 100% stock legos it's not possible, but with over-volted motors without the internal planetary gear reduction it might work.  The vehicle will basically be a missile though.  Good luck not destroying it in testing.

[Sariel]

The guy who wrote the second post in this topic is a Boeing engineer. If he says it can't be done, then it can't be done, end of story. Not to mention that your post sounds very theoretical, I mean no offense but what's your experience in building fast LEGO cars? Have you achieved at least half of your goal, that is 25 mph?
And to answer your question: I don't know what wheels you mean by "mindstorms" wheels but really large LEGO bike wheels with 11.5 studs of diameter will require about 5,000 RPM to reach 50 mph. This might help in your future calculations: https://play.google.com/store/apps/details?id=pl.sariel.brickgearratiocalculator

[TechnicRCRacer]

@Sariel I think the author means 2903 which came in many of the old RCX sets.

[FoxOne]

6 hours ago, TechnicRCRacer said:

@Sariel I think the author means 2903 which came in many of the old RCX sets.

Could be wheels from RI / Spike Prime also.

[ukbajadave]

On 11/6/2020 at 9:10 PM, Mark adler said:

....buggy motors....direct drive on both axles...

...What rpm do I need to reach 50 mph?...

My copy of The Unofficial Technic Builders Guide by @Sariel lists the buggy motor specs at 9V as 1053 RPM or 780 RPM depending on inner or outer output.

50 Miles per hour is about 80.5 Kilometres per hour. Divide by 60 to get distance in one minute (to match RPM) gives us 0.83 Miles or 1.341 Kilometres. Divide distance by revolutions gives us circumference of wheel, 127.36 cm or 171.94 cm depending on output used. The circumference gives us the radius (20.27cm or 27.37cm) which we double for a diameter. Then we use Sariels Unit converter to turn it into studs. So using a directly driven axle from the buggy motor to hit 50 MPH you need wheels of approx 50 (inner drive) or 70 (outer drive) stud diameter. Obviously Lego doesn't make a wheel in this size so here is the solution.

4 of these bad boys should see you hitting 50 in no time. As a bonus they are very light weight which will help with acceleration of rotational mass.