RC receiver (part 8884) whining sound and not driving motor

[Crazybill]

Hi all.

I downloaded the 3D model and built a modified RC version of Lego 42005 shown in this link http://www.eurobricks.com/forum/index.php?showtopic=88490

I used an L-motor (88003) and IR receiver (8884), but I had to use alternative parts for the other 3 power function parts as I don't have them:

I used Battery pack 8881 (instead of 8878) - for powering the whole thing

I used Medium motor (8883) instead of servo motor (88004) - for controlling the wheel direction

I used Remote control 8879 (instead of 8885)

What happens is that if I connect the units directly to the battery pack, the model drives fine (the L-motor), but the wheels don't turn very nicely at all (unless there's very little resistance, as when I hold the model in the air).

So I guess using a regular motor instead of a dedicated servo one isn't a good choice.

The real problem however is when I connect the thing using the RC; the IR receiver unit sounds a high pitched noise and the motors don't spin at all, unless I hold the car in the air (and that also is a hit and miss. especially for turning the wheels).

Can anyone please explain what I'm doing wrong? Is the remote control faulty (it's came from a train set, dunno if this means anything), is the battery pack too weak (I used freshly charged batteries), is a regular motor inadequate to simply turn an axle if the turning range is limited (the wheels are already all the way to the right/left)?

Thanks for helping out!

[dr_spock]

The train remote provides 7 levels of power. Did you try turning the knobs until it gets to full power?

[Crazybill]

The train remote provides 7 levels of power. Did you try turning the knobs until it gets to full power?

Thanks for replying!

To your question - yeah, I did.

That's the only way the wheels *sometimes* get enough juice to drive (using the L-motor). I say *sometimes* because usually it does this whining noise in this case as well.

As for the m-motor controlling the direction: it whines all the time when connected via the IR receiver.

[NXT45]

Thanks for replying!

To your question - yeah, I did.

That's the only way the wheels *sometimes* get enough juice to drive (using the L-motor). I say *sometimes* because usually it does this whining noise in this case as well.

As for the m-motor controlling the direction: it whines all the time when connected via the IR receiver.

That happens to me the motor is stalling from lack of torque. Your best bet is to buy a servo motor.

[Captainowie]

There shouldn't be an issue using a M motor in place of a servo motor, but you shouldn't expect to be able to just swap motors and get the same performance. You'll need to gear down the M motor somewhat to get enough torque.

As far as the whining noise goes, I'm afraid I can't help you. It's possible that your receiver might be faulty if the model drives OK without the receiver and not OK with it.

[750ACE]

Use a different 8881 battery pack. I had a new one with my 9398 that wasn't putting out the correct current causing the exact same issues. Changed packs and used same batteries, my problem was solved.

[Crazybill]

when you say you had the exact issues you mean the whining noise etc.? is this a known issue? because apart from the the renote control, all parts are brand new.

as to gearing down the m motor to get enough torque, can anyone please explain how it is done and explain the main difference between a regular motor and a servo one?

[DrJB]

... as to gearing down the m motor to get enough torque, can anyone please explain how it is done and explain the main difference between a regular motor and a servo one?

I'd simplify as much as I can. An electric motor is a transducer, in a sense that it takes electrical power (voltage×current) and converts it into mechanical power (torque×rpm). As such, an electrical motor does not deliver speed nor torque. It delivers power instead. Now, how much torque/RPM depends on the mechanical load applied to that motor. In fact, each motor has a torque-rpm characteristic, which says how fast the motor spins, depending on how much load you apply to it (The converse is also true). Such power is the MAX (constant) a motor can deliver. If you want to get max torque from a motor, you need to slow it down, not by applying a smaller voltage, but by putting a series of gears to drop the RPM. There will be losses due to friction and so on, so any gear train you insert after a motor is bound to cause losses.

... explain the main difference between a regular motor and a servo one?

A regular motor spins continuously as long as there is voltage applied to it. A servo motor rotates a given angle and stays there, it does not keep on moving. Maybe another way (under max voltage):

1. A regular motor will spin at MAX speed, and keeps on rotating until you disconnect it.

2. A servo motor will move to its max rotation angle (not speed) and keep that position until power is disconnected, then it returns to center.

Hope this helps, otherwise ask again.

Edited December 28, 2014 by DrJB

[Crazybill]

DrJb, that was an excellent explanation.

I truly appreciate the time and effort you put into typing it. Thank you!

I thought as much regarding the servo motor. It truly is the tool of trade for what I'm trying to achieve here so I guess I'll buy one.

[750ACE]

Yes I said same issues but with L-motors whining and stalling. As stated my parts were brand new as well. If you are using an M motor on a V2 receiver in place of a servo motor I am not certain it will work properly without gearing down.

Edited December 28, 2014 by 750ACE

[DrJB]

DrJb, that was an excellent explanation.

I truly appreciate the time and effort you put into typing it. Thank you!

I thought as much regarding the servo motor. It truly is the tool of trade for what I'm trying to achieve here so I guess I'll buy one.

Very welcome, glad I could help. Now, I must add that, in the past, before the servo motor was introduced, and in applications where you can't have a motor keep on rotating e.g., steering, people have used a regular motor with a friction 20-teeth gear in between, That way, when the driven component reaches the max allowable position, the motor keeps on spinning (and is not blocked) and yet the clutch gear transmits no rotation.

[dr_spock]

Have you tried using a 8885 IR remote instead of the train speed remote?

Are your batteries showing "good" when tested with a battery tester?

Have you checked for friction in your model?

[Crazybill]

I don't own any other remote, the batteries ate perfect, the model works OK without the RC. but the steering is clunky. Yeach, I know, gotta get a servo motor for that. Little place for making any modifications anyway

[Infraredbrick]

The real problem however is when I connect the thing using the RC; the IR receiver unit sounds a high pitched noise and the motors don't spin at all, unless I hold the car in the air (and that also is a hit and miss. especially for turning the wheels).

Can anyone please explain what I'm doing wrong? Is the remote control faulty (it's came from a train set, dunno if this means anything), is the battery pack too weak (I used freshly charged batteries), is a regular motor inadequate to simply turn an axle if the turning range is limited (the wheels are already all the way to the right/left)?

I had the exact same issue (the high-pitched sound from the receiver) on one of my MOCs. I think you're going to need to use the IR receiver V2, not the one you have.

[Crazybill]

I had the exact same issue (the high-pitched sound from the receiver) on one of my MOCs. I think you're going to need to use the IR receiver V2, not the one you have.

Thank you very much! When I bought the receiver I didn't even know there were 2 versions...

Thanks to all the other contributors as well. This is an excellent forum!