PF IR-receiver limits

[Tobbe Arnesson]

Hi!

Tried to find out how many motors that can be attached to one IR-receiver port.

I found that Zblj mentioned 0.8 A as max for the receiver here: http://www.eurobricks.com/forum/index.php?showtopic=48347&view=findpost&p=850838

Is that per port, i.e. you can get that x 2 from each receiver? Is there a source on this (not that I don't trust Zblj)? I looked at Philos page about PF but it said nothing.

Looking at the motor data from Philo: http://www.philohome.com/motors/motorcomp.htm

Medium PF motor under load: 0.31 A.

XL PF motor under load: 0.55 A.

IF 0.8 A is per port you can use:

Two medium per port, three if they don't work so hard.

One XL per port, two if they don't work so hard.

Almost one medium and one XL per port.

However Philo don't say anything about how much of strain this load test is on the motors, I suppose it can be a lot higher until it peaks in stalled state (that data exists on Philos page, but it does not matter if the receiver shuts off if the motors stall).

Any thoughts on this subject?

[JopieK]

It seems to be that LEGO is using an older H-bridge IC for the receiver, new bridges emerge nowadays that seem to be very powerful (look at sparkfun or pololu e.g. to see that they even have 13A motor drivers for 12V or so).

[tl8]

It seems to be that LEGO is using an older H-bridge IC for the receiver, new bridges emerge nowadays that seem to be very powerful (look at sparkfun or pololu e.g. to see that they even have 13A motor drivers for 12V or so).

New or old is not the problem. The main problems within the receiver are:

a) The actual size of the enclosure. This is a big problem and can be one of the hardest to visualise (Even as an engineer)

b) Thermal considerations. There is no airflow inside the receivers and the H-Bridges can dissipate many watts of power (The small surface mount resistors are rated for 0.25W but would be emitting no where near that much). If the IC dissipates too much power (More than the plastic case can remove) then the enclosure can overheat and damage the parts inside.

c) Cost. Electronics are relatively cheap until you start using special components. It is important to keep your stocks up and always be on the lookout for potential replacements if required. Any replacement would also need to be tested and approved to ensure it is of the same standard.

Is there room for improvement in the receivers?

Defiantly. However I suspect that Lego is lacking in electrical engineers and doesn't want to pay the high cost of a consultant for something that works just fine.

[Tobbe Arnesson]

I'm sorry, but could we keep this thread about what the receivers is today and not about what they could be?

[tl8]

Hi!

Tried to find out how many motors that can be attached to one IR-receiver port.

I found that Zblj mentioned 0.8 A as max for the receiver here: http://www.eurobricks.com/forum/index.php?showtopic=48347&view=findpost&p=850838

Is that per port, i.e. you can get that x 2 from each receiver? Is there a source on this (not that I don't trust Zblj)? I looked at Philos page about PF but it said nothing.

Looking at the motor data from Philo: http://www.philohome.com/motors/motorcomp.htm

Medium PF motor under load: 0.31 A.

XL PF motor under load: 0.55 A.

IF 0.8 A is per port you can use:

Two medium per port, three if they don't work so hard.

One XL per port, two if they don't work so hard.

Almost one medium and one XL per port.

However Philo don't say anything about how much of strain this load test is on the motors, I suppose it can be a lot higher until it peaks in stalled state (that data exists on Philos page, but it does not matter if the receiver shuts off if the motors stall).

Any thoughts on this subject?

Sorry about the diversion, thought the thread was an older one

Most likely that would be per receiver. That would be the maximum current that the single chip can provide.

Edit: http://www.eurobricks.com/forum/index.php?showtopic=46030&view=findpost&p=804761

The datasheet for the driver IC is here.

Looks like your bog standard H bridge driver. Nothing really unusual here.

Edited December 1, 2010 by tl8

[Tobbe Arnesson]

Is there an old topic on this subject? I tried searching but I could not find any good keywords and got tons of results or nothing...

Don't know how to read the data sheet but if I understand this correctly:

Output sustaining voltage VO (sus) IOUT = 400 mA 9 V

Then we should not even be able to use one XL motor per port?

[tl8]

Is there an old topic on this subject? I tried searching but I could not find any good keywords and got tons of results or nothing...

Don't know how to read the data sheet but if I understand this correctly:

Output sustaining voltage VO (sus) IOUT = 400 mA 9 V

Then we should not even be able to use one XL motor per port?

Not quite. That is a test condition. So when Io is 400mA the Minimum Vo is 9V. The maximum current that can be sinked (which is not how it is set up) is 1.0A. When used as a H brigde (which it is) then the maximum supply current is 800mA.

This datasheet is a bit confusing mainly because of the allowable operating voltages.

[Fistach]

Well for me current allowed by IR receiver is high enough to not bother about it.

[Tobbe Arnesson]

Thanks tl8!

But if the 0.8 A is for the whole receiver it would not be possible to use two XL motors attached to each port simultaneously since that would amount to 1.1 A?

[tl8]

Thanks tl8!

But if the 0.8 A is for the whole receiver it would not be possible to use two XL motors attached to each port simultaneously since that would amount to 1.1 A?

They would not be at full power. Either by a lower voltage or a current limit (and hence a lower current drawn by the motors). It would depend on the protection provided by the chip and the circuit what version is used.

So in a nutshell, 2 XL motors will run but not at full power.

[Tobbe Arnesson]

Yikes, that's bad news!

Thanks for clearing this up.

Now you can discuss what the receiver should be, it seems it's in need for better performance!

[Zerobricks]

Yikes, that's bad news!

Thanks for clearing this up.

Now you can discuss what the receiver should be, it seems it's in need for better performance!

Dont forget the battery box also has a current limiter at arround 1 Amp.

[Tobbe Arnesson]

Great...

Oh well, I still love the RC stuff!

[2LegoOrNot2Lego...]

Well this all explains a lot to me. I tried to put more power in my Heavy Duty Truck. Since it has to drag so much weight more motors = more power is . It did not seem to have that much effect, it appears not to work at all. Now that I read this thread I know why...

In this truck I used 2 XL motors connected to only one receiver. With this knowlegde there is no need for 2 XL motors any more. Maybe I try to give it one more receiver, but next the battery box will be the problem... Why all these limits anyway, I need all the power I can get...

[Zerobricks]

For max power use the RC unit... Its quite rare, but it has no limiters!

Edited December 1, 2010 by Zblj

[SuperCow]

You could use 2 ir-receivers to power 1 motor

link

Edited December 1, 2010 by SuperCow

[2LegoOrNot2Lego...]

For max power use the RC unit...

I have one of the RC units, but any ideas on how to squeeze it in there...

Thanks for the advice off course, but there is no way to put it in these models, much to small...

You could use 2 ir-receivers to power 1 motor

Well that make sense and might actually work, but next is the battery box limit. So for powering 2 XL motors at there max, I need 2 battery boxes and 4 IR receivers since I have installed 2 XL motors...

My current budget does not allow me to buy Lego 8878 rechargeable batteries. In the future I might want to install 2 of these, replacing the battery box I use now (it is almost equal in dimension). Install one more IR receiver, this will help quite a lot... Installing 2 receivers per XL motor (I use 2 XL's, so 4 receivers are required ) is not realy an option.

At the moment I can not change a thing, but again this topic helped me quite a lot, thanks to all...

[Blakbird]

Well that make sense and might actually work, but next is the battery box limit. So for powering 2 XL motors at there max, I need 2 battery boxes and 4 IR receivers since I have installed 2 XL motors...

You should take a look at Sariel's Leopard Tank. He uses 4 PF-XL motors powered by two battery boxes through two IR receivers. Sounds like just what you'd like to do.

[dhc6twinotter]

This is some good info! The moc I just finished uses two XL motors and an m motor on one IR receiver. So far, it seems to work ok, but maybe that is just because none of the motors are under a whole lot of stress.

For my next project, I was planning on running two XL motors on the same channel, with a separate IR receiver and battery box for each motor. Would this be sufficient? I'm not sure I completely understand why I would need 2 IR receivers for one XL motor.

Thanks,

Daniel

[Crtlego]

This is very interesting indeed. In my 8 Wheeler I had all wheel drive which consisted of 4 Xl motors and steering which is 1 M motor. I had all of these, 5 in total, going through to one Receiver and one Battery Box.. It seemed to work fine but I guess you never actually be able to tell the difference by just looking at it..

[rgbrown]

In this truck I used 2 XL motors connected to only one receiver. With this knowlegde there is no need for 2 XL motors any more. Maybe I try to give it one more receiver, but next the battery box will be the problem... Why all these limits anyway, I need all the power I can get...

Two independent PF circuits with receivers on the same channel (2 battery boxes) is one option

EDIT:

Sorry, I didn't read the thread properly - many have suggested this already

Edited December 2, 2010 by rgbrown

[Milan]

So, if we want to power the vehicle with 2 XLs, and one Receiver's port, and one battery box, the power of XL's are not fully exploited?

What is the conclusion...? Is it better to just use 1 XL on one port on one battery box?

[tl8]

So, if we want to power the vehicle with 2 XLs, and one Receiver's port, and one battery box, the power of XL's are not fully exploited?

What is the conclusion...? Is it better to just use 1 XL on one port on one battery box?

Yes. That will ensure maximum current and maximum power. A lot however will depend on the application of the motor.

[Tobbe Arnesson]

How about the old 9 V battery packs, do they also limit the current? For those high power applications perhaps they are a better choice and let an IR-connected motor only control a polarity switch between the old battery pack and the motors? Then you can also put two battery packs in series to get 18 V, but that can be really hard on the motors...

Get's pretty big and hard to hide in models...

[Milan]

Yes. That will ensure maximum current and maximum power. A lot however will depend on the application of the motor.

Application for XL is powering a heavy vehicle.

Can you provide theoretical difference between 1XL-1port-1BB with 2XL's-1port-1BB, regarding motor performance on a heavy model?