Power Supply

[Brian Porter 2Participant @brianporter2]

Which batteries & converter? Two novices!

[Brian Porter 2Participant @brianporter2]

Hi, forgive our lack of knowledge but are we’re slowing moving up the modelling ladder!

We’re building a 93cm Torpedo Patrol Boat (K D Perkasa). We have two brushed MFA 850 motors, two MTronics Viper Marine 40 ESCs plus a MTronics W-Tail mixer. We’re committed to using Nimh batts. We’re thinking (just for the motors & ESCs) two 7.2v 5000 Nimh in series to achieve 12v but clearly we have a 2.4v excess.

So, we’re looking for advice on a recommended converter and would gratefully welcome all and other additional advice please – many thanks.

[Colin BishopModerator @colinbishop34627]

Component Shop sell 6v 5000MAh power packs:

**LINK**

You could run one to each motor.

Colin

[Brian Porter 2Participant @brianporter2]

Thanks Colin, ah ah, sounds perfect. The link brings up 12v but I’ve found the 6v version (out of stock!!) so I’ll call them. We really appreciate your help.

[Colin BishopModerator @colinbishop34627]

They will make you up custom versions if you ask. They made me up a split version to tuck into the bilges of my Fishery Cruiser to keep the weight low down.

From your post I thought you were looking to run the motors on 12v as specified.

The 12v pack can be used to deliver 12v to both motors. It's just the same as sticking two 6v packs together in series.

Colin

 

Edited By Colin Bishop on 09/04/2021 16:35:29

[ashley needhamParticipant @ashleyneedham69188]

The only thing I would say is that whereas a 12v pack is handy, if one cell dies, the whole lot is useless, and they are not cheap. Personally I would buy 2x 6v packs, that way if one dies you just have to buy one as a replacement.

The motors should handle 14V as per two 7.2v packs as long as you dont run them at full power for hours.

Ashley

[Colin BishopModerator @colinbishop34627]

Not quite useless Ashley, you can always replace the affected cell but I take your point.

As you say, the motors should be able to take 14.4 volts for short periods but many radios allow you to set the endpoint on the various channels using dual rate so you can limit the voltage that way.

Colin

[Charles OatesParticipant @charlesoates31738]

I wouldn't go for the two 7.2 packs the viper is only rated to 12 volts and 14.4 will probably ruin them.

Charles

[ashley needhamParticipant @ashleyneedham69188]

Good point Charles!,

i bought a 24v esc for the Fantome so I could use 2×7.2 packs for a bit more oomph.

Ashley

[Brian Porter 2Participant @brianporter2]

Thank you all, this is so helpful. We want 12v for each motor so will run batteries in series.

Charles is certainly right, I asked MTronics earlier today & they were clear their Viper 40 ESCs are 12v max & no more plus their W-Tail mixer is 5v max (not mentioned in their leaflet).

We thought two 6v so we have some equal ballast each side together with the two motors. We’ll also be using the 12v for our ShockWave3 sound board.

Obviously we’ll add smaller addition batteries for the receiver & other other very small low voltage/amp extras.

Thanks again to you all, we’re learning here with your kind help.

Brian

[ashley needhamParticipant @ashleyneedham69188]

Brian. The esc have a BEC facility in them to supply the receiver so no additional batteries are necessary although some like to use a separate battery pack. If using this facility, one of the bec wires will have to be cut as you only need one to supply the receiver.

Dont forget a 5v supply for very low current drain items, leds etc is available from the receiver on a spare or battery channel.

Ashley

[Brian Porter 2Participant @brianporter2]

Ashley, thanks for the BEC reminder. While speaking to MTronics yesterday he also made a point of mentioning that I need to cut the red wire between each of the ESCs & the mixer.

Brian

[Malcolm FraryParticipant @malcolmfrary95515]

I hope he only said "ONE of the red wires". Unless running a separate supply, the 5 volts needed for the mixer, radio and anything else plugged into the radio has to come from somewhere, and that is usually the ESC that still has its BEC.

Actually cutting the red wire is a mistake. Much better to winkle the wire and its terminal out of the plug and tape it back in a tidy manner. Much easier to reconnect if that ESC plus its BEC is needed in the future.

[Brian Porter 2Participant @brianporter2]

Both wires as the 5v mixer will be supplied from the same power source as the receiver. Yes, by “cut” I should perhaps say disconnect as you suggest plus your’ll be impressed to learn I have spare pins & plugs if I mangle it !

I appreciate your advice.

Brian

[Brian Porter 2Participant @brianporter2]

Has anyone the patience to read this? Feel free to laugh & criticise!

We’re moving forward but here’s the latest operational variations & we’re now stuck –

1) Motor(s) powered direct from 12v = silent & perfect running

2) Motor powered by ESC = runs ok but also whistles. Same when run together with Y connector

3) With mixer using Outputs 1 & 2 (as per leaflet) = only one motor works & also whistles

4) With mixer using Outputs 2 & 3 both motors run (whistling) but unequally

5) Steering – using Y connector from RX to mixer & servo, steering works fine in all the above examples but has no effect on motor speed

6) Remove mixer & replace with Y connector = Both motors run equally (fwd & rev) but still whistle.

NOTE – All setup instructions for ESC(s) & mixer followed. Have also discovered ESC outputs 5v to RX so only one wire disconnected & so obviously our planned separate power supply for RX is not needed, in fact Carson book says do not use separate supply. That bit was easy!

Does anyone have the patience to help??

Brian & Mathew

[Malcolm FraryParticipant @malcolmfrary95515]

1, 2, 3, 4 & 6. Motor whistling under ESC control. Yes, they do. In the extreme elder days, a motor speed was controlled by wasting power in a resistance element which had to be very closely matched to the motor. Nowadays, the variation in power is got by switching the supply on and odd VERY rapidly. Due to the constraints of the electronics involved, this usually results in a coil held in a strong magnetic field being moved in a series of steps at a frequency that is audible. Older ones didn't work just as well, but ran on a lower frequency and rumbled. Different motors differ in their susceptibility to produce sound, but since all motors contain the same elements as loudspeakers, they all do it. Just that some are louder than others. Some ESCs you don't hear, but passing dogs might.

Personally, I appreciate the whistle. It lets me know that something is going to happen.

All devices that plug into a receiver run on the timed pulses coming from the receiver. A mixer, in theory, takes the timing from the throttle channel, and looks at the pulses coming down the rudder channel. If the rudder channel pulse is saying "go straight", the throttle channel just passes its information along, unadulterated, to both ESCs. If the rudder channel is giving a longer or shorter pulse, indicating a turn, then the mixer adds a bit to one output, and subtracts a bit from the other which tells the ESCs to change their outputs.

The number of possible permutations is scary. I tend to break things down in an effort to get my logic straight by using a couple of servo testers as known supplies for the signals instead of the radio. Radio switches and added computer controls do muddy the logic somewhat.  

The other handy items are a pair of servo Y leads and a pair of spare servos.  These can be used as meters to look at what signals are being passed round the system, and in the case of ESCs, you get to see what they are being offered and are not stuck with just observing the motors behaviour.  Much problem solving consists of finding ways to break a sequence down and finding out why actuality has diverged from theory.

Edited By Malcolm Frary on 11/04/2021 14:11:35

[Brian Porter 2Participant @brianporter2]

Malcolm, thank you so much for that both interesting & educational info. I love to understand properly.

That said, clearly the only problem we have then is with this mixer, The supplied instructions are simple & you’ve helped reaffirm our theory on how this should work but it doesn’t. I guess I can give MTronics a call tomorrow but if you or anyone else have any ideas or experience with this W-Tail Mixer we’d be grateful for any advice.

Ultimately this mixer is an extra that’s certainly not critical so if need be we’ll just abandon it but that seems a bit defeatist & a waste of £16!

Brian

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