Tarix819

Questions on hardcoupling

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Hi, new here! :laugh:

I am a big fan of building Lego Technic RC cars but have a few (probably stupid) questions:

When hardcoupling two motors, is a separate battery box required for each motor to improve the mechanical power?

If I only use one battery box to drive both motors does is the power split between them?

What are some ways of reducing stress on a drivetrain to prevent gears from slipping and grinding?

Thanks,

Nick

Edited by Tarix819

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My experience with hardcoupling is that you got definitally a litlle more torc .

BUT: not every motor is reliable to get the same rpm. (so would you risk it?)

1 batterybox is enough for powering two (XL) motors (300 ma x 2). batterybox delives 800 Ma.

Reducing stress on the drivetrain is to get a good ratio. (slowing down the rpm with small gear to big gear)

and use 2 gears on 1 axle instead of 1). my own project requires a lot of power, and i used 2 gears instead of 1

But with rc cars that drive fast, maybe a clutch gear will help to prevent damaging the gears at a sudden stop of yur rc car

U also can use the knob gears. they have zero slip.

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Here are some answers:

  • When you hardcouple, you split capacity of power.
  • No two motors are the same, so there is small risk.
  • Two batteries will time more power, but don't forget the extra weight can outweigh the gain.
  • Less gears 100%. Smaller tires give less friction, but less speed. The small tires also give better acceleration.

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1. No, two battery boxes are not required, at least some of the time. Sometimes it is needed, but not usually. All Lego power supplies have limits to how much power they can output, and sometimes you have a combination of motors that can exceed that limit, in which case the battery will have its thermal protection kick in.

2.No, that's not how it works. However, sometimes you have 2 motors that draw more current than the battery can supply. However, if that's not the case, the motors will run at full power.

3. This is a hard question to answer generically. However, there exists a book by our own @Sariel called The Unofficial Lego Technic Builder's Guide, which includes a chapter describing this. Some further advice is to keep drivetrains as short as possible, and do gear reduction as close to the end function as possible.

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14 minutes ago, Saberwing40k said:

1. No, two battery boxes are not required, at least some of the time. Sometimes it is needed, but not usually. All Lego power supplies have limits to how much power they can output, and sometimes you have a combination of motors that can exceed that limit, in which case the battery will have its thermal protection kick in.

2.No, that's not how it works. However, sometimes you have 2 motors that draw more current than the battery can supply. However, if that's not the case, the motors will run at full power.

3. This is a hard question to answer generically. However, there exists a book by our own @Sariel called The Unofficial Lego Technic Builder's Guide, which includes a chapter describing this. Some further advice is to keep drivetrains as short as possible, and do gear reduction as close to the end function as possible.

 

16 minutes ago, Aventador2004 said:

Here are some answers:

  • When you hardcouple, you split capacity of power.
  • No two motors are the same, so there is small risk.
  • Two batteries will time more power, but don't forget the extra weight can outweigh the gain.
  • Less gears 100%. Smaller tires give less friction, but less speed. The small tires also give better acceleration.

 

18 minutes ago, Techniccrack said:

My experience with hardcoupling is that you got definitally a litlle more torc .

BUT: not every motor is reliable to get the same rpm. (so would you risk it?)

1 batterybox is enough for powering two (XL) motors (300 ma x 2). batterybox delives 800 Ma.

Reducing stress on the drivetrain is to get a good ratio. (slowing down the rpm with small gear to big gear)

and use 2 gears on 1 axle instead of 1). my own project requires a lot of power, and i used 2 gears instead of 1

But with rc cars that drive fast, maybe a clutch gear will help to prevent damaging the gears at a sudden stop of yur rc car

U also can use the knob gears. they have zero slip.

Thanks very much for the quick responses, that clears it up nicely.

I think the biggest problem I'm having is the complex drivetrain, which is using the old linear gear changing system (no driving rings) and is constructed mostly of the old 1970 - 1990 lego technic, so I will look for some ways to make it more resistant to high torque.

Thanks! :thumbup:

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1 hour ago, Techniccrack said:

My experience with hardcoupling is that you got definitally a litlle more torc .

BUT: not every motor is reliable to get the same rpm. (so would you risk it?)

 

The difference between motors, RPM-wise, is fairly negligible.  Present, yes, but fairly minimal, and the resistance on the slower motor really isn't much different than the regular resistance used in most applications. 

 

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No problem with hardcoupling at all, the motors will simply help eachother.

I've got a 1700gr car driven by 4 L motors, two hardcoupled pairs each driving one rearwheel, it drifts with the wide Porsche tires and takes off bloody fast.

Two L motors can be driven from 1 V2 IR receiver, for 4 L motors I simply use two V2 IR receivers set on the same channel.

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1 hour ago, Permo said:

No problem with hardcoupling at all, the motors will simply help eachother.

I've got a 1700gr car driven by 4 L motors, two hardcoupled pairs each driving one rearwheel, it drifts with the wide Porsche tires and takes off bloody fast.

Two L motors can be driven from 1 V2 IR receiver, for 4 L motors I simply use two V2 IR receivers set on the same channel.

Unfortunately I don't own any V2 IR Receivers. I understand that they allow two motors to run at full power whilst connected to the same port?

If I use 2 regular V1 IR Receivers and connect one motor to each will it achieve the same effect as 1 V2 IR Receiver?

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It will help a lot yes.

From the top of my head V1 allows 800mA and V2 allows 3500 mA.

So simply use two set to the same channel.

Also the is a thermal fuse in the batterybox itself, which will limmit performance, I run my models from a 11.1V Graupner LiPo which can put out a whopping 140A

See it in action here;

Video is at the bottom of the page, also found a solution for a drivetrain that can handle the torque, it can be seen in the pics.

Cheers ! Happy racing !

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1 minute ago, Permo said:

It will help a lot yes.

From the top of my head V1 allows 800mA and V2 allows 3500 mA.

So simply use two set to the same channel.

Also the is a thermal fuse in the batterybox itself, which will limmit performance, I run my models from a 11.1V Graupner LiPo which can put out a whopping 140A

See it in action here;

Video is at the bottom of the page, also found a solution for a drivetrain that can handle the torque, it can be seen in the pics.

Cheers ! Happy racing !

Thanks! :laugh: :thumbup:

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6 minutes ago, Tarix819 said:

If I use 2 regular V1 IR Receivers and connect one motor to each will it achieve the same effect as 1 V2 IR Receiver?

no it wont, the v2 simply allows more current per channel, That is why the 9398 crawler needed the v2, it has 2 L-motors on 1 channel, so the servo can be on the 2nd. It can deliver more amps than a v1 receiver, so it can power more motors, however the battery box is still limiting the current unless you have a LiPo box.

maybe running 1 motor off 2 v1 receivers will do the trick, but it does not sound like a good idea to me, that would mean an "electric hard-couple" ;) (never tried it, but sounds doable with 2 extension cords and a 9v lead-plate, and of course the correct polarity at all times..)

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No do not run 1 motor from two V1 receivers, simply use one receiver per motor.

if you want to overcome the thermal protection in the batterybox you can remove (bypass) the fuse or simply use two batteryboxes feeding two IR receivers.

I tried all of that and eventually got me a third party LiPo (much cheaper than the Lego options)

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1 minute ago, Permo said:

No do not run 1 motor from two V1 receivers, simply use one receiver per motor.

if you want to overcome the thermal protection in the batterybox you can remove (bypass) the fuse or simply use two batteryboxes feeding two IR receivers.

I tried all of that and eventually got me a third party LiPo (much cheaper than the Lego options)

 

9 minutes ago, Marxpek said:

no it wont, the v2 simply allows more current per channel, That is why the 9398 crawler needed the v2, it has 2 L-motors on 1 channel, so the servo can be on the 2nd. It can deliver more amps than a v1 receiver, so it can power more motors, however the battery box is still limiting the current unless you have a LiPo box.

maybe running 1 motor off 2 v1 receivers will do the trick, but it does not sound like a good idea to me, that would mean an "electric hard-couple" ;) (never tried it, but sounds doable with 2 extension cords and a 9v lead-plate, and of course the correct polarity at all times..)

I think I should be okay since I only want to power 2 L-Motors which, assuming the V1 Receiver allows 800mA, should be fine as L-Motors are about 300-400mA each. 

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Just now, Permo said:

No do not run 1 motor from two V1 receivers, simply use one receiver per motor.

agreed ;) but i must try to see what happens later on ;D

@Permo you mention that the v2 can power 2 L-motors, but isn't that 2 L-motors per port? like in the crawler? so it can power 4 of them total right?

@Tarix819 what type of motors gearing and weight will you be using? 

1 minute ago, Tarix819 said:

should be fine as L-Motors are about 300-400mA each. 

i think that is what they draw whit the battery box turned off :wink:, aren't they the most inefficient motors around? apart from buggys ofc..

But in general a v1 should be enough to power just 2 L-motors, maybe with insane gearing it will cause issues, but should be fine.

To get back on hardcoupling motors: i happily hard-coupled 4 buggy motors powered by 2 different rc-units and set a speed record with it, so i would not worry about it and hey, if it breaks, it breaks.. lesson learned.. next?

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Well I tried that, but there is also a thermal protection in the V2 receiver and it kicked in during acceleration from stand still with 4 L motors (1700gr Lego model)

So I split the load over two V2 receivers and it runs like a rocket.

The IR receiver put out a PWM voltage (squarewave) from an IC (chip) if you couple the outputs it means that one receiver will blast it's output into the other receivers chip, it might blow the PWM chip so my advise would be not to test this.

Coupling two batteryboxes into one receiver is no problem.

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Just now, Marxpek said:

 

@Tarix819 what type of motors gearing and weight will you be using? 

My vehicle has 3 gears: 

1st gear: 1:3 

2nd gear: 1:1

3rd gear: 3:1

At the end of the drivetrain a 20-tooth gear connects to a 28-tooth differential with the ratio 1:1.4.

In first gear the vehicle drives fine, the second gear the vehicle drives fine, however in third gear the vehicle will not move unless travelling down a slope. When I add more motors or use an XL motor (Instead of the single L motor I am currently using) the drivetrain simply breaks. The vehicle weighs about 1.4kg.

Also keep in mind for changing gear I am not using driving rings, I am using a linear gear system similar to that of the 8860 Auto Chassis model.

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20 hours ago, Aventador2004 said:

Here are some answers:

  • When you hardcouple, you split capacity of power.
  • No two motors are the same, so there is small risk.
  • Two batteries will time more power, but don't forget the extra weight can outweigh the gain.
  • Less gears 100%. Smaller tires give less friction, but less speed. The small tires also give better acceleration.

Kind of a stupid question, but from where did the term “hard coupling” come from in the Lego community? I look up “hard coupling” on google and I see nothing about connecting motors together with gears, which seems to be what the subject is here.

This question has baffled me ever since I joined the Lego Technic community. There seems to be some divide between Lego Technic terminology and what’s known by the “rest of the world”. Same thing for subtractors, that mechanism for driving tanks. I look up “subtractor” I google and all I see are the LEGO mechanisms. Surely the terminology would have originated because of previous innovations - this term just spontaneously popping up in the LEGO technic community just seems strange.

Can someone please explain the origins of some of these terms when used in LEGO technic?

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1 minute ago, JLiu15 said:

Kind of a stupid question, but from where did the term “hard coupling” come from in the Lego community? I look up “hard coupling” on google and I see nothing about connecting motors together with gears, which seems to be what the subject is here.

This question has baffled me ever since I joined the Lego Technic community. There seems to be some divide between Lego Technic terminology and what’s known by the “rest of the world”. Same thing for subtractors, that mechanism for driving tanks. I look up “subtractor” I google and all I see are the LEGO mechanisms. Surely the terminology would have originated because of previous innovations - this term just spontaneously popping up in the LEGO technic community just seems strange.

Can someone please explain the origins of some of these terms when used in LEGO technic?

It comes from Sariel's book: 'The Unofficial Lego Technic Builder's Guide' I think.

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1 minute ago, JLiu15 said:

Kind of a stupid question, but from where did the term “hard coupling” come from in the Lego community? I look up “hard coupling” on google and I see nothing about connecting motors together with gears, which seems to be what the subject is here.

This question has baffled me ever since I joined the Lego Technic community. There seems to be some divide between Lego Technic terminology and what’s known by the “rest of the world”. Same thing for subtractors, that mechanism for driving tanks. I look up “subtractor” I google and all I see are the LEGO mechanisms. Surely the terminology would have originated because of previous innovations - this term just spontaneously popping up in the LEGO technic community just seems strange.

Can someone please explain the origins of some of these terms when used in LEGO technic?

Just called that for so long, became they are literally coupled together in a solid way.

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Just now, Aventador2004 said:

Just called that for so long, became they are literally coupled together in a solid way.

So Sariel essentially “introduced” some terminology into the LEGO Technic community?

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Just now, JLiu15 said:

So Sariel essentially “introduced” some terminology into the LEGO Technic community?

Not necessarily, I heard it on some very old topics.

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5 minutes ago, Tarix819 said:

In first gear the vehicle drives fine, the second gear the vehicle drives fine, however in third gear the vehicle will not move unless travelling down a slope. When I add more motors or use an XL motor (Instead of the single L motor I am currently using) the drivetrain simply breaks. The vehicle weighs about 1.4kg.

are you gearing up remotely on the move? or are you trying to drive off in the 3rd gear? the gearing does not sound that extreme to me but might be on the edge for 1 L-motor.

The size of the wheels are kind of important here, but i have a feeling you are using big ones, else it should have no problem moving.

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5 minutes ago, Aventador2004 said:

Not necessarily, I heard it on some very old topics.

So terms like “pendular suspension”, “adder/subtractor”, “hard coupling”, etc did spontaneously arise in the LEGO technic community?

I’ve never seen those terms applied to real-life mechanisms

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Just now, Marxpek said:

are you gearing up remotely on the move? or are you trying to drive off in the 3rd gear? the gearing does not sound that extreme to me but might be on the edge for 1 L-motor.

The size of the wheels are kind of important here, but i have a feeling you are using big ones, else it should have no problem moving.

I've tried both gearing up on the move and moving from stationary in 3rd gear and it has the same effect. The wheels are very large, they are the classic foam tyre wheels found on the 8865 Test Car, 8860 Auto Chassis and 853 Auto Chassis. 

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1 minute ago, Tarix819 said:

The wheels are very large

you might add heavy there ;D

My best guess is you are hitting some kind of thermal protection, either in the L-motor, the ir- receiver or the BB.

Will it move in the 3rd gear if you power if purely from the battery box, leaving the receiver out?

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