4 XL motors, one channel of a PF receiver?

[andythenorth]

Anyone run 3 or 4 XL motors on a single channel of a PF receiver in a trial truck or similar?

Lego don't advise it (http://powerfunction...aq/default.aspx), and I thought I'd read somewhere that the PF receiver current protection will trip with more than 2 XL motors, but can't find that with google.

I'm not concerned about damaging the parts, but I don't want to build a toy where the PF will cut out a lot due to current protection kicking in

I have tried 4 XL on one channel, and they run fine, if a bit slowly. 3 is slower than 2 and, 4 is slower again, the battery box can't keep up. So performance might be an issue too.

I also tried stalling 2 of the 4 motors (using finger as a brake, errr don't try that at home, blisters). That does trip the receiver if I do it long enough. Dunno if the truck I'm building will stall motors long enough for this to be a problem, I think it will break gears rather than stall a motor.

Main problem could be battery life / power? I am wondering if more power can be patched in to the power rails on the PF wire?

Edited May 10, 2013 by andythenorth

[Nazgarot]

Use two PF recievers, or use a servo to controll a switch (PF switch or the battery box switch) directly connecting the four motors to one or more battery boxes.

This should give you enough power to run the motors. I would also recommend using the V2 receiver that was launched along with the crawler, as that will give you about 30% more power to the motor. (It will however require using more than one battery box as there is a limiter in the battery box as well).

-ED-

[Splat]

You can use two battery boxes, and two receivers both set to the same channel so they both receive the same signal. Then each receiver has two motors attached to it. This will also double your batteries so they will last longer, but will be heavier.

[efferman]

or you use an servo and a power function switch to power the XL

[andythenorth]

The servo-switch solution is nice, but I want to use the proportional speed remote. Maybe a PF rotary proportional switch is needed? :)

This truck will have two battery boxes anyway, so that suggestion could work. From experience with PF trains, I wonder if the two receivers will get out of sync easily?

[Splat]

The servo-switch solution is nice, but I want to use the proportional speed remote. Maybe a PF rotary proportional switch is needed? :)

The only proportional switch with PF is the speed adjustment that is on the rechargeable battery box (8878). You could use a servo motor powered from one battery box to turn the speed adjustment on the other rechargeable battery box, and the rechargeable battery box provides power to the XL motors. You are still limited by the 2 XL motors per battery box, so now you need 3 battery boxes - one for the IR receiver and servo motor, one for the first 2 XL motors, and one for the second 2 XL motors.

This truck will have two battery boxes anyway, so that suggestion could work. From experience with PF trains, I wonder if the two receivers will get out of sync easily?

If you are using the proportional remote (train remote - 8879), then there is a chance that the speeds could get out of sync, even if both receivers are placed right next to each other. If you are using the 'bang bang' remote (8885), then there is a better chance that they will stay in sync as they sync up again each time you let go of the remote controls - at least that is what I am hoping for in a MOC that I am working on at the moment.

[Boxerlego]

The web site will tell you that the 8881 battery box has a current limit of 800ma. Now every time you add a motor to the battery box the battery box must supply the addition current for that motor. Now 1 XL motor draws around 300ma from the battery box. If you were to use 4 XL motors that would be 4X300ma=1200ma total from the battery box and that exceeds the 800ma limiting fuse. Watch the two videos below and you will see it.

Edit: But with the neodymium magnets we do not see the 800ma fuse limitation.?

Edited May 13, 2013 by Boxerlego

[andythenorth]

Thanks for the info. The truck is now more complete, I have 3x PF motors on one channel, single battery box. This should exceed the max current for the battery box? So far that hasn't happened. Tests include:

- brief stall (few seconds) from driving the truck against a wall

- climbing up a 2 inch vertical obstacle

- towing a 3 year old on a scooter

Batteries are 6 x 1.2v AA NiMh rechargeables, full charge. If I = V / R, and max voltage is 7.2v, and R is assumed fixed...that limits max current?

Edited May 18, 2013 by andythenorth

[Ape Fight]

I run 4x XLs and 1x M, 3 from 1 battery box and receiver, and 2 from the other. Otherwise the M (steering) motor gets its current nicked and fails to perform when under full load.

Edited May 18, 2013 by Ape Fight

[andythenorth]

Thanks Ape Fight, that's useful info. Nice truck too.

[Nazgarot]

Thanks for the info. The truck is now more complete, I have 3x PF motors on one channel, single battery box. This should exceed the max current for the battery box? So far that hasn't happened. Tests include:

- brief stall (few seconds) from driving the truck against a wall

- climbing up a 2 inch vertical obstacle

- towing a 3 year old on a scooter

Batteries are 6 x 1.2v AA NiMh rechargeables, full charge. If I = V / R, and max voltage is 7.2v, and R is assumed fixed...that limits max current?

What receiver are you using? The V2 receiver delivers more power to the motors, and should pull more from the battery box...

-ED-

[andythenorth]

What receiver are you using?

It's v1. I can lay my hands on a v2 though. Will try it.