RC motor & PF

[MarcoB]

I build a RC car with one RC motor and with PF IR receiver etc.

It was fun to drive with it because it was light-weighted so skidding was easy, you could do "burnout" circles too

Everything worked fine but after a while car started to malfunction:

Even I pushed throttle on, motor did not run continuously, it made stops (on/off) in about 1-2 seconds intervals.

At first I didn't understand what is going on, assumed that something is interfering IR signal, batteries low or something.

Then, by accident, I sniffed the IR receiver and it had a burn smell, an electronic burn smell.

After that, I have not used RC motor with any PF parts..

Luckily, IR receiver still (seems to) work's, at least with PF components.

This site also warns about RC motor usage:

"Not recommended for use with a RCX which can't deliver the current needed by this beast."

Well, RC motor consumes almost twice the current than a PF XL motor

Has anyone came across the same problem?

Does anyone know about the specs for power function components (current limits etc) ?

[Zerobricks]

PF receiver has a curent limit of 800mA which sii not enough for a beast like RC motor, si it shuts down untill the limit is passed again, therebye making the typical on off pulses.

[MarcoB]

PF receiver has a curent limit of 800mA which sii not enough for a beast like RC motor, si it shuts down untill the limit is passed again, therebye making the typical on off pulses.

OK, that really explains the behaviour AND why my receiver is still working!

It's good to know that there IS a protective circuit in the receiver. Applauses for Lego!

So you can use RC motor with PF, BUT that consumes receiver more than PF motor(s), and may stop to function (for ever) some day

Thanks Zblj for the info!

[JopieK]

Hmm that RC motor can draw up to 3.2A according to Philohome :) well that is quite something. The XL motor just up to 1.8A (but is indeed limited by itself and the IR receiver).

Greetz Johan

[Jurgen Krooshoop]

I noticed the same "drup-outs" with my small red racecar which also uses an RC-motor. Never noticed the burning-smell though (fortunately) and all the PF-components still work. I've heard stories about a stalled RC-motor draining an 8878 within an fraction of a second, so I guess RC + PF is a nifty combination.

[rgbrown]

I've heard stories about a stalled RC-motor draining an 8878 within an fraction of a second, so I guess RC + PF is a nifty combination.

Really? The 8878 has an overcurrent dropout too ... well at least I'm pretty sure it does, but all the product specs seem to be gone from powerfunctions.lego.com.

Where are those pages that have detailed descriptions of each PF element? Am I just incompetent at browsing TLG website, or are they actually gone?

[Crtlego]

I don't remember which moc it was that I used my RC motor in but I remember experiencing the same thing.. but without the smell or at least I don't remember there being a smell..

The on and off thing I have definitely encountered before but I remember it staying off for longer than 1 or 2 seconds..

I built a truck trial truck, which I will post soon, that uses the RC motor to drive all four wheels. There is a worm gear system involved and works perfectly because not only do I have speed but I have power.

The only problem is when I get to something really tough and it doesn't want to run you can hear the hesitation in the motor's vrrrrrr sound.. Eventually it just comes to an expected stop when the stress is too high.

I developed a system to work around this but it uses quite a lot of space and is currently not very efficient. I connected the motor to a PF switch and motorized the switch with an M Motor and connected the M Motor to the PF Receiver. The switch then goes to the battery box. This allows you to control, not very accurately though, the RC motor without stalling...

It works but like I said takes a lot of room.