Vintage BEC?

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Vintage BEC?

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6 May 2017 at 18:57 #5473
Paul75
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@paul75
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6 May 2017 at 18:57 #70910
Paul75
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@paul75
Hello Everyone.

I've taken it upon myself to refurbish a 1/96th scale Battle class destroyer from the early 1980s. This is fitted with a 27MHz 2 channel RC set up which works well.

On a 6V drive battery the pace of this model is rather sedate and I was looking to install a 7.2V NiMH battery pack. However, before I do this, I would just like to check that the voltage to the receiver will not exceed 6V.

The model was fitted with the RC circuit shown in the photo below (I've removed the rudder servo lead).

The receiver is a Futaba FP-R2GS and the ESC is a Futaba FP-MC5, both from the early 1980s. The servo lead between the receiver and the ESC has its three wires connected to receiver. The "BATT" receiver lead runs to a simple switch which itself has no auxiliary power supply, so I'm guessing this serves only to complete the receiver power circuit when the switch is closed.

Does the vintage ESC installed have BEC functionality? I'd guess that it does but given its age I can't find this spec online.

Any help would be much appreciated.

Many thanks,

Paul.
6 May 2017 at 19:21 #70913
ashley needham
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@ashleyneedham69188
Paul. Who knows about the BEC facility?. The BATT lead that goes to a switch may be a clue that there should be an external battery pack used to power the receiver, the switch is simply to turn this on or off.

If in doubt, disable the red wire on the lead from the ESC, and use a separate battery pack.

If the destroyer has a sedate performance on 6v then fitting a 7.2 pack will increase this but only a little bit. Any idea what motor has been fitted? A speed increase may be had by changing the prop. The original (obviously I cant see what this is) may be mismatched to the motor or deficient in another area.

Ashley
6 May 2017 at 21:22 #70915
Paul75
Participant
@paul75
Thanks for your reply Ashley.

There's no receiver battery fitted yet everything works which is why I reckon the ESC must have BEC. As for the motors, the model has 2 "Modelsport Falcon" motors fitted which are of 540 type dimensions but again I can't find the exact specs online. I would guess they are 540s given the vintage of the model. With the ESC rated at maximum voltage supply of 7.2V this is most battery voltage I can use with this set up.

I take your point about the prop size, pitch etc but as I've got a spare 7.2V NiMH battery pack in my workshop I thought I'd try this first an see what the performance is like with this fitted.

Many thanks,

Paul.
6 May 2017 at 22:05 #70916
Kev.W
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@kev-w
Paul, as the ESC will not be harmed by using 7.2, remove the plug from rec. BATT socket, fit 7.2 batt to ESC, & use meter to check voltage supplied to pins on rec. plug.

This will tell you if BEC is indeed fitted, or whether the full 7.2 is being passed to rec.

Edited By Kip Woods on 06/05/2017 22:06:07
7 May 2017 at 09:24 #70919
Malcolm Frary
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@malcolmfrary95515
I very much doubt whether a BEC is in the ESC. Simplest way to check is to use a voltmeter and measure the voltage at the receiver pins. If it 5 volts, a BEC is involved, if 7.2 volts is shown, there isn't. The receiver might have an internal BEC to allow itself to work on the higher voltage, but that is not something that I would consider trusting.

Going off the vintage, it probably uses and suffers from the same transistors as the Hitec Gold Brick. The voltage limitation there was due to the power that the resistors driving the output transistors needed to dissipate. All of the ones that were shown to me had big black burn marks where the resistors used to be, usually caused by running the thing on its highest rated voltage. Or more..

There is probably a very good case for doing a comprehensive refit involving radio, ESCs and servos, much like hat happens with real warships.

To scale, I would expect that on 6 volts, under load, the motors should be pulling about 10 Amps. If the basic power is not there, the performance won't be, either. Back in the elder days, just having the model go was a triumph, having it go like it should and under control was luxury. Now, it is expected.
7 May 2017 at 10:16 #70920
Dave Milbourn
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@davemilbourn48782
A bit of Googling revealed that the FP-MC5 ESC is a forward-only 20A speed controller with brake. It was identical to the Robbe Rocar 12 except that the Robbe unit also had reverse. This write-up clearly indicates that the Rocar 12 had BEC – implying that the MC5 also had it – **LINK**
This makes sense, given that Paul's model has only the one battery (6v) fitted. Back in the early 80's all model electronics was based on the computer industry standard component operating voltage of 5v. It's only relatively recently that 'high-voltage' receivers and servos have appeared. I'd go along with the voltage test suggested by Malc F and Kip.
Well, that's not quite true…. I'd personally sling the thing away and fit a modern Fwd+Reverse unit, along with a 2G4 radio! In my experience a 30+ year-old 27MHz radio is a problem just waiting to happen – even if it's a Futaba.

Dave M
7 May 2017 at 11:22 #70922
ashley needham
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@ashleyneedham69188
Yes, a replacement ESC would be in order, and you will have reverse then as well. While you are at it, a wattmeter would not go amiss to check the current draw of your motors. What size and type are the props??
Ashley
7 May 2017 at 20:53 #70925
Paul75
Participant
@paul75
Thanks for your replies.

As per Kip's suggestion, I tested the voltage at the ESC receiver plug on 6V and 7.2V and got a steady 5.8V for both battery voltages. I've installed my 7.2V drive battery and tested the boat on the water and it goes along very nicely. I was also slightly surprised that the motors were barely warm after 15 minutes of use as I was expecting them to be hot at this voltage.

Thanks again for your help,

Paul.
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