Drifting G-class

[FriedlS]

Hello, 

i like to show you my version of a drifting G-Class. Bodywork design is by https://rebrickable.com/mocs/MOC-111437/_.lego._.technic._/mercedes-benz-g-class/#details

i just did some modifications to fit my 4wd chassis with rc components.

propulsion: buggy motor 

steering: geek servo

receiver: Radiolink 

battery: 7.4V LiPo

here are some pictures:

 

and a clip:

 

Hope you like it 😊

Cheers, Friedl

 

[gyenesvi]

This looks better in red than in black :)

Can you give some details about the electronics? I'd like to try Geekservo for steering, and I assume I need RC components for that, what I have yet to figure out is how to control the propulsion motor in that case? Is it just that you need to connect some output of the receiver to the motor by connecting some cables? Or is there some other component needed for converting signals?

For example, I have been comparing the Geekservo and the Lego servo, and it seems to me that they are using different PWM methods, and hence they cannot be simply mixed and matched. Is it simpler for the plain DC motors?

[pow]

Nice presentation.

is it possible to take a picture from below. i wonder what the steering angles look like.

[FriedlS]

2 hours ago, gyenesvi said:

This looks better in red than in black :)

Can you give some details about the electronics? I'd like to try Geekservo for steering, and I assume I need RC components for that, what I have yet to figure out is how to control the propulsion motor in that case? Is it just that you need to connect some output of the receiver to the motor by connecting some cables? Or is there some other component needed for converting signals?

For example, I have been comparing the Geekservo and the Lego servo, and it seems to me that they are using different PWM methods, and hence they cannot be simply mixed and matched. Is it simpler for the plain DC motors?

Thank you very much!
 

you can see the electronic parts here (except the geek servo changed):

I use a receiver e.g. Radiolink and a esc where you can connect the battand the motor. In my case i changed the wires at the motor to bec connector for the esc.

I never tried to connect a Lego servo with this receiver, soi can’t say how the wires have to be changed. Geek servo has got three wires (+, -, s), lego servo has got four.

Hope this is helpful for you.

1 hour ago, pow said:

Nice presentation.

is it possible to take a picture from below. i wonder what the steering angles look like.

Thank you very much!
There is a photo of below, which detail do you want to know?

[aFrInaTi0n]

Hello Friedl, nice MOC again and looking like plenty of fun :D

 

I am so much thinking about switching from Buwizz to regular RC components some times.. Your picture gives me the thought that the efforts will basically be to just exchange the cables/connectors of the Motors..

The ESC is a 'Pichler Brushed ESC 30A" (Specs: https://www.pichler.de/PDF/C9342) or something? Just to go with this as a basis for further question: Limitation in voltage then would be like 9.4V right?

Any recommendations for an ESC that allows to go to ~12V (I guess 14.8V for a 4S then as power source)?

Other question regarding the transmission: Is it still the good old 24Mhz like we all remember from the RC hobbies days from our youth? :D

[FriedlS]

19 minutes ago, aFrInaTi0n said:

Hello Friedl, nice MOC again and looking like plenty of fun :D

 

I am so much thinking about switching from Buwizz to regular RC components some times.. Your picture gives me the thought that the efforts will basically be to just exchange the cables/connectors of the Motors..

The ESC is a 'Pichler Brushed ESC 30A" (Specs: https://www.pichler.de/PDF/C9342) or something? Just to go with this as a basis for further question: Limitation in voltage then would be like 9.4V right?

Any recommendations for an ESC that allows to go to ~12V (I guess 14.8V for a 4S then as power source)?

Other question regarding the transmission: Is it still the good old 24Mhz like we all remember from the RC hobbies days from our youth? :D

Thank you very much! 😊

The Transmitter and receiver are 2.4Ghz, it is more popular these days 😉

The ESC spec is for use with 2s Lipo. I tried a 3s Lipo, it works but the temperature of the ESC parts got warm in shorter time and it smelled not good.

I ordered this ESC AS12/15RW BEC EASY which should also work with 3s.

The advantage of the 2s ESC is, it is small.

In my opinion it is very simple to change the wires at the fake buggy motor and i also removed the thermal resistor. 
Until there is no analog controller for 3rd party battery hubs it is the best alternative for me. 😊

[pow]

let me explain:
I am just finishing my current MOC. And from this I now have an unused virtual pivot steering left, which I thought could fit well into a drift car.
The steering I have in mind steers the cornering inner wheel significantly(!) more than the cornering outer wheel. See picture:

Your drift cars don't. The front wheels are very parallel at all steering angles. But they seem to work very well. I have also looked at your other vehicles on Youtube. What I noticed is that your cars have a very strong caster.
Is the Ackermann geometry not as important as I thought and the caster plays a greater role? Or is it just the sheer power of your engines (and some scotch tape on the wheels)?

[aFrInaTi0n]

Thanks for the details. As the frequency question may already sugested, never went back to rc hobbies since the 90s 😅

Size depends then again also on capacity, but may be a good point that with the default sizes available it will be too much capacity and therefore size for my needs where weight & size unfortunately matters.. :D

I generally so much would like tohave the ability to give complete analog input (and without lag and range issues which Buwizz unfortunately has 😫).

@pow Its called an Ackermann-Lenkung (https://en.wikipedia.org/wiki/Ackermann_steering_geometry)

Does it keep the outer wheel straight the whole distance? Or am I getting it wrong as it just showing the difference in the cornering, but would both corner?

[pow]

@aFrInaTi0n I guessed the question would come. The Picture is misleading. Both wheels have to corner (I hope they do to be honest ). This was just a quick build to underline, what i'm thinking of.

BTW: Thanks for the hint on Ackermann geometry, including the link. Did i get your intention wrong, because i mentioned the name in my post.

Best wishes

[gyenesvi]

13 hours ago, FriedlS said:

I use a receiver e.g. Radiolink and a esc where you can connect the battand the motor. In my case i changed the wires at the motor to bec connector for the esc.

I never tried to connect a Lego servo with this receiver, soi can’t say how the wires have to be changed. Geek servo has got three wires (+, -, s), lego servo has got four.

Thanks for the info, so the Geekservo is connected directly to the receiver, but the Buggy motor needs the ESC to be inserted in between to properly control it if I get it right. I wonder why the servo does not need a separate controller. Anyway, it's great that the Buggy motor can be connected by changing the cable ending. I guess it would be possible to make a converter wire with one end as a lego connector, the other as a RC connector in order to alleviate the need to cut the wires of the Buggy motor. Would this also work with a PF M/L/XL motor?

[2GodBDGlory]

3 hours ago, gyenesvi said:

I guess it would be possible to make a converter wire with one end as a lego connector, the other as a RC connector in order to alleviate the need to cut the wires of the Buggy motor.

It would definitely be possible, but at some point you might have to worry about having high current melt down the wimpy Lego plug. I ran into that recently running two buggy motors off of one plug off of an RC car controller on a 3S lithium battery, so I had to solder a beefier plug in in parallel with the Lego one.

[FriedlS]

19 hours ago, pow said:

let me explain:
I am just finishing my current MOC. And from this I now have an unused virtual pivot steering left, which I thought could fit well into a drift car.
The steering I have in mind steers the cornering inner wheel significantly(!) more than the cornering outer wheel. See picture:

Your drift cars don't. The front wheels are very parallel at all steering angles. But they seem to work very well. I have also looked at your other vehicles on Youtube. What I noticed is that your cars have a very strong caster.
Is the Ackermann geometry not as important as I thought and the caster plays a greater role? Or is it just the sheer power of your engines (and some scotch tape on the wheels)?

@pow
An Ackermann steering geometry would be possible with my construction. I tried it, but there weren’t any advantages in order of the handling. A positive caster angle helps to drive forward especially after cornering. So my rear wheel drive cars have got a positive caster angle. This G-class doesn’t have.

Here you can see the steering angle:

 

1 hour ago, 2GodBDGlory said:

It would definitely be possible, but at some point you might have to worry about having high current melt down the wimpy Lego plug. I ran into that recently running two buggy motors off of one plug off of an RC car controller on a 3S lithium battery, so I had to solder a beefier plug in in parallel with the Lego one.

@gyenesvi
I can confirm this. The main problem is the limited PF connector. But you can also do this with any other PF motor.

17 hours ago, aFrInaTi0n said:

Thanks for the details. As the frequency question may already sugested, never went back to rc hobbies since the 90s 😅

Size depends then again also on capacity, but may be a good point that with the default sizes available it will be too much capacity and therefore size for my needs where weight & size unfortunately matters.. :D

I generally so much would like tohave the ability to give complete analog input (and without lag and range issues which Buwizz unfortunately has 😫).

@pow Its called an Ackermann-Lenkung (https://en.wikipedia.org/wiki/Ackermann_steering_geometry)

Does it keep the outer wheel straight the whole distance? Or am I getting it wrong as it just showing the difference in the cornering, but would both corner?

@aFrInaTi0n

I totally agree with the issue that there is no analog controller for BuWizz.

Another advantage of this small ESC is that it has got a power switch and also a switch for activating the motor brake when you go from forward to backwards.

Edited November 17, 2022 by FriedlS

[Alex Ilea]

This is super cool, nice ride!

[FriedlS]

@Alex Ilea thank you very much😊

 

[gyenesvi]

8 hours ago, 2GodBDGlory said:

It would definitely be possible, but at some point you might have to worry about having high current melt down the wimpy Lego plug. I ran into that recently running two buggy motors off of one plug off of an RC car controller on a 3S lithium battery, so I had to solder a beefier plug in in parallel with the Lego one.

7 hours ago, FriedlS said:

I can confirm this. The main problem is the limited PF connector.

Hmm, thanks guys for the warning, but there's something that I don't understand. Why would such a scenario put higher current to the PF connectors than they were designed for and than when they are used with a PF system or with a Buwizz for example? Is it that the ESC can control the motors in such a manner that they draw more current, while the Lego / Buwizz system does not? If yes why?

[2GodBDGlory]

23 minutes ago, gyenesvi said:

Hmm, thanks guys for the warning, but there's something that I don't understand. Why would such a scenario put higher current to the PF connectors than they were designed for and than when they are used with a PF system or with a Buwizz for example? Is it that the ESC can control the motors in such a manner that they draw more current, while the Lego / Buwizz system does not? If yes why?

Yeah, I was wondering about that too.
In my case, the problem might have been that I was running two buggy motors off of the same plug, which would double the current there, but in general I'm not sure. According to E = IR, given a fixed voltage no higher than Buwizz outputs, and an equal resistance from the motor, the current ought to be the same, shouldn't it?

[pow]

@2GodBDGlory https://philohome.com/motors/motorcomp.htm says each buggy motor pulls 1.4A at 9V so two eat twice as much. 2.8A over such a thin cable may be enough to warm it up. But do they run at 9V or even more?

@FriedlS thanks for the picture. and the helpful information. I will definitely experiment with som caster angles.

Edited November 18, 2022 by pow

[msk6003]

14 hours ago, gyenesvi said:

Thanks for the info, so the Geekservo is connected directly to the receiver, but the Buggy motor needs the ESC to be inserted in between to properly control it if I get it right. I wonder why the servo does not need a separate controller. Anyway, it's great that the Buggy motor can be connected by changing the cable ending. I guess it would be possible to make a converter wire with one end as a lego connector, the other as a RC connector in order to alleviate the need to cut the wires of the Buggy motor. Would this also work with a PF M/L/XL motor?

Because servo motor has controller inside of it's casing. And RC servo and lego servo's work is very different. RC servo work by PWM signal from receiver but lego servo is work by voltage level from receiver. This is why lego servo has 4 wire and cause use voltage level insted direct PWM, receiver can easily control all motors by simply regulating the voltage without having to detect which motor is connected.

[2GodBDGlory]

2 hours ago, pow said:

@2GodBDGlory https://philohome.com/motors/motorcomp.htm says each buggy motor pulls 1.4A at 9V so two eat twice as much. 2.8A over such a thin cable may be enough to warm it up. But do they run at 9V or even more?

Yeah, they are running at 12V peak, but I don't think that would increase current. Though I suppose it might increase heat for other reasons? It would be interesting to directly measure the amp pull with my multimeter; maybe I will soon. It is likely, though, that the 2.8 was just too much for the connector...

[pow]

@2GodBDGlory This chart from the link above shows that the current increases with higher voltages (but not much to be honest).

5292	Torque	Rotation speed	Current	Mechanical power	Electrical power	Efficiency
4.5 V	5.7 N.cm	150 rpm	1.36 A	0.87 W	6.12 W	14 %
6 V	5.7 N.cm	380 rpm	1.38 A	2.27 W	8.28 W	27 %
7.5 V	5.7 N.cm	580 rpm	1.37 A	3.45 W	10.3 W	34 %
9 V	5.7 N.cm	780 rpm	1.40 A	4.61 W	12.6 W	37 %
10.5 V	5.7 N.cm	1030 rpm	1.46A	6.16 W	15.3 W	40 %

i wonder why the stackable plugs for the buggy motors were allowed to be used at all.

Edited November 18, 2022 by pow

[2GodBDGlory]

36 minutes ago, pow said:

This chart from the link above shows that the current increases with higher voltages (but not much to be honest).

5292	Torque	Rotation speed	Current	Mechanical power	Electrical power	Efficiency
4.5 V	5.7 N.cm	150 rpm	1.36 A	0.87 W	6.12 W	14 %
6 V	5.7 N.cm	380 rpm	1.38 A	2.27 W	8.28 W	27 %
7.5 V	5.7 N.cm	580 rpm	1.37 A	3.45 W	10.3 W	34 %
9 V	5.7 N.cm	780 rpm	1.40 A	4.61 W	12.6 W	37 %
10.5 V	5.7 N.cm	1030 rpm	1.46A	6.16 W	15.3 W	40 %

i wonder why the stackable plugs for the buggy motors were allowed to be used at all.

Oh, interesting!
I wonder if the old original 9V plugs would hold up to higher current any better than the PF-style ones on my Chinese motors.

[pow]

@2GodBDGlory hm, good question. the old 9V plugs are very similar to the PF plugs. And the cables also have a very slim cross-section.
It would also be interesting to know at which point the plugs become warm. Perhaps there is a certain place on the connector is made particularly thin and the electrons must squeeze through there.

Edited November 18, 2022 by pow

[2GodBDGlory]

1 hour ago, pow said:

@2GodBDGlory hm, good question. the old 9V plugs are very similar to the PF plugs. And the cables also have a very slim cross-section.
It would also be interesting to know at which point the plugs become warm. Perhaps there is a certain place on the connector is made particularly thin and the electrons must squeeze through there.

Maybe we should switch to some other thread or PM after this, but I've never found the wires to be the weak link, always the plugs. The PF plugs just have one small contact, but if I remember correctly the 9V plugs have two contacts per side, so you'd think maybe they could get close to double the current. (Though they're also close enough that they might share the heat a fair bit anyways.

[pow]

@2GodBDGlory that's a good idea. But i can't help that much more on that topic. my knowledge ends exact here.

but for general amusement I dug up this old topic about melted plastic.

 

[FriedlS]

@pow and @2GodBDGlory the problem of higher voltage and the buggy motor is, that as you can see at the list above, the electrical power rises very much. But the efficiency isn’t 100% so you have got also lost power. E.g. electrical power at 10.5V is 15.3W. Efficiency is 40% so you have got 38.25W lost power (approximately). This means you generate 53,55W to get 15,3W electrical power. The most of the lost power is heat ( and a part is friction) which must be handled by all electrical parts. And here are the PF Connectors the weak part.

At 9V you get 12.6W electrical power with an efficiency of 37%. So you have got 34.05W lost power. So you have got approximate 11% less  lost power as at 10.5V. This is a lot and this may be the reason why it can works with 9V but you will get trouble with higher Voltage.

To be honest my electrotechnology lessons were several years ago, so i guess not everything is exactly right. But this is the way i try to explain the problems with the combination of higher voltage and buggy motor and PF connectors.

Update:

One point may be not right in my explanation, the efficiency may be the comparison between electrical and mechanical power. So the lost power may be lower as i mentioned but it will increase with higher voltage.

Another point is that the contact resistance of the PF connector may be very high. So at higher voltage you produce more lost power at the connectors, i guess. 

 

cheers, Friedl 😊

Edited November 19, 2022 by FriedlS