The state of electric setups today.

[machasm]

Hi all,
I have been thinking about rx packs, servos and rx setups for a while and have made some observations which seems to point to a few potential problems based on the hardware used today. Let me explain further.
When RC modelling began I can only assume that the current demands by the servos and rxes of the day were much less demanding than the are today.
The leads, and in particular the servo connectors all have a small but measurable resistance but were ample to cope with the demands of yesteryear.
Fast forward to today where we are running HV servos with unbelievably hi torque values with matching high current demands and these connectors begin to pose a bit of a bottleneck.
In particular if the setup is all running of a single unit (say a 3GX or other fbl unit) and power is supplied to the unit from a BEC or direct from a battery through a single servo lead. This could potentially lead to a brown out! Since the voltage dropped across that connector could feasibly be enough to drop the rx below its operating voltage as the battery draws close to its lower operating voltage at the end of a flight.

So a few questions.
1) Why haven't there been systems developed that allow for hi current connections to the system (at least to the RX itself, although I am aware that spektrum do some such as the AR7100R etc)?
2) Why don't more people use LiFe (aka A123) setups to eliminate the need for regulators and hance another point of failure and more connections?
3) Are the power buses in the FBL units capable of handling the current demands of 1 stalled HV servo let alone 3 or even 4?

Your thoughts.
Ade.

[SGD]

The same questions have crossed my mind more than once even though my fleet doesn't include any HV set ups and my style of flying wouldn't push these systems anyway.
But putting together a 550 recently got me looking at the concerns regarding ESC BEC capabilities and many of them seem to have a marginal power output at best with lots of people suggesting the use of a separate BEC or a battery backup with them.

Can't answer 1 and 3 but I do use LiFe's on my nitros and have considered them for electric as well but I would prefer to reduce the number of items we bolt, stick and strap to my models to reduce the number of connections and simplify the wiring.
A single Rx/FBL with gov/ESC with good BEC/built in power backup unit sounds good to me and if it can make a good cup of tea even better!

[steve_b]

This is the reason I use these Gryphon Extreme-Heli Voltage Regulator GVR-7020B so that I plug the servos into the regulator instead of relying on connections to the Rx.

On some of ym other helis I use Jives and use the Throttle and slave connectors so that have a 10Amp supply to the servos and Rx as the connectors that are normally used are only rated at 5 Amps.

[Mark_T]

In particular if the setup is all running of a single unit (say a 3GX or other fbl unit) and power is supplied to the unit from a BEC or direct from a battery through a single servo lead.

Easy answer is don't wire it that way

I know people will still do that, but it usually isn't hard to arrange at least 2 power connections from the source.

Solutions like the Gryphon as Steve mentioned are another easy way around the issue.

[machasm]

Personally I don't. I have 2 cables going to the Rx from a lipo.
as regards the reg. still seems like not the best solution really. Ok there is a larger gauge wire from batt to reg but you still have the 5A connectors from reg to servos. You are also introducing yet another piece of kit to go wrong.
i remember shelling out really good money on a Scott Gray reactorX reg only to have a solder joint on the pcb fail and stick my 700N in a couple of years ago.
i think the whole system needs a bit of a overhaul where a new, higher rated connector is used on high torque servos, as well as beefing up the wires and buses in the Rx/fbl units.
i know that this will cause compatibility issues with everything everybody has out there but we could always use an adaptor until the new models are phased in (yes I am aware that that means more points of failure!).

Easy answer is don't wire it that way

I know people will still do that, but it usually isn't hard to arrange at least 2 power connections from the source.

Solutions like the Gryphon as Steve mentioned are another easy way around the issue.

[p4ddy]

Easy, ditch your FBL unit & HV servo's etc.

[jimmyhorns]

Its not a million years ago when we didnt have a generic connector, and generic wiring....

The only significant problem most of us face is having to trim off the polarity lip on a futaba type plug to make it fit

I still have some Sanwa servos that have a different polarity on the same plug, when things were not uniform, and if you go a little further back (to before I was born) you can see an array of servo connectors that were brand specific and didnt always use the same signalling protocols/spec from the Rx...

The very fact that we have now a system where pretty much everything talks to everything else in the same language with the same basic connectors is a godsend....

The 5A ratings on the connector do not include peak demands which are very shortlived unless a servo has stalled, and your servos shouldnt be able to stall in normal use..... The introduction of HV servos actually reduce the current required for a given working load, so I cannot see why for a given application, using HV servos is going to result in a greater nominal current draw.

I just dont think that manufacturers would want to go back to a proprietary system for connecting stuff together. It sucks because you are tied to one manufacturer, or have to have many conversion leads, which again are yet another source of failure.

[Mark_T]

The point about the Gryphon and one or two others is that they split the power bus from the signal side.

Yes, it is something else to go wrong, but you are no longer running the full servo current across the receiver bus.

You can also do something similar with passive wiring if you are so inclined but it does become a bit of a rats nest.

The roughly 3A limit on the servo connector does remain a bottleneck though I agree.

Problem is, once you change that connector it opens up a world of compatibility issues ...

[dani_r]

I've never had any problems with my setups. I don't use HV servos but I do use a CC BEC Pro on all my helis. 1 connection goes to the Rx and the other to the FBL, or sometimes both in to the FBL unit.

I think with regular maintenance checks you should be able to minimise the risk of failure in most areas, but obviously not all.

Each to their own I suppose. I personally don't like Life packs as I like to keep a close eye on the capacity of all my power packs. Life doesn't allow you to do that very easily, it relies on you knowing the mah usage so far etc which doesn't compute for me. If you forget, or something goes wrong, you have a problem. But again, each to their own.

[RcRotaryMadness]

Hi all,

In particular if the setup is all running of a single unit (say a 3GX or other fbl unit) and power is supplied to the unit from a BEC or direct from a battery through a single servo lead. This could potentially lead to a brown out! Since the voltage dropped across that connector could feasibly be enough to drop the rx below its operating voltage as the battery draws close to its lower operating voltage at the end of a flight.

People are aware of this issue and so if they are running a high demand setup often use at least two battery to FBL power connections. On my setup I actually use three.. two to the Vbar and one to the RX.. so the Vbar technically has 3 power supplies all distributed evenly across its power bus.

So a few questions.
1) Why haven't there been systems developed that allow for hi current connections to the system (at least to the RX itself, although I am aware that spektrum do some such as the AR7100R etc)?
2) Why don't more people use LiFe (aka A123) setups to eliminate the need for regulators and hance another point of failure and more connections?
3) Are the power buses in the FBL units capable of handling the current demands of 1 stalled HV servo let alone 3 or even 4?

Your thoughts.
Ade.

a1) The plugs we use are pretty much an industry standard and all servos/rxs/fbl units etc all use them. So to change isn't going to be easy or may not be accepted. Also using methods described above you can work round the issue. In time they may well introduce higher current plugs but for now its fine as it is.

a2) Personal choice.. some people only want one flight battery to plug in and have done with (don't want the hassle of another battery). Others do use a LiFe pack as they don't want the risk of a BEC failure. Those on a HV setup tend to use a direct 2S lipo. So its mostly personal choice.

3) I have not gone out and tested it as I don't want to risk burning out a vbar but I would say the power bus is able to supply enough current for most applications and brief stalled servos (in a crash or such like). If 1 or all 4 servos are stalled then clearly there's a big problem and something WILL burn out, whether it be the servos themselves, the power bus or the wiring.. if somethings stalled like that then something will get burned out so it will be whatever the weakest link is.

Matt

[pgkevet]

I don;t see why you can't have the signal down the power wire and the whole airframe negative to the battery and just use single wires with mini-bullets after a life to the rx. servo cases as ground too... ultimate simplicity?

[RcRotaryMadness]

I don;t see why you can't have the signal down the power wire and the whole airframe negative to the battery and just use single wires with mini-bullets after a life to the rx. servo cases as ground too... ultimate simplicity?

Yeah this could be possible as like in a cars electrics but i think the risk of a short would be high? If one cable rubbed on the frame it would short..

[Planehazza]

I've never had any problems with my setups. I don't use HV servos but I do use a CC BEC Pro on all my helis. 1 connection goes to the Rx and the other to the FBL, or sometimes both in to the FBL unit.

I think with regular maintenance checks you should be able to minimise the risk of failure in most areas, but obviously not all.

Each to their own I suppose. I personally don't like Life packs as I like to keep a close eye on the capacity of all my power packs. Life doesn't allow you to do that very easily, it relies on you knowing the mah usage so far etc which doesn't compute for me. If you forget, or something goes wrong, you have a problem. But again, each to their own.

Very true, but as you use a similar setup to me (VBar and Align servos) I can tell you, that even on your goblin 700, you won't use more than ~180mAh per flight. I use 130mAh, but you're a better pilot and will chuck it round a little more. My fusion uses 110mAh, and my rush 700 uses about 130-140mAh. I'm using a 2100mAh 2S LiFe, and I stop using it after 4 flights to be safe. Same with the Fusion, and that's only 1100mAh! Eek!

[jimmyhorns]

I don;t see why you can't have the signal down the power wire and the whole airframe negative to the battery and just use single wires with mini-bullets after a life to the rx. servo cases as ground too... ultimate simplicity?

It wouldnt be straightforward to super-impose (multiplex) signal onto the +ve wire, as the electronics behind the multiplexing would need to be capable of high current draw, adding to weight, size and expense....

There isnt really any magic to the positive power feed or bus, its essentially just a load of connectors all joined together, by having a signal superimposed it would make this impossible.

[Varelco]

The 5A ratings on the connector do not include peak demands which are very shortlived unless a servo has stalled, and your servos shouldnt be able to stall in normal use..... The introduction of HV servos actually reduce the current required for a given working load, so I cannot see why for a given application, using HV servos is going to result in a greater nominal current draw.

Not true. HV servos pull more current than a regular servo. Typically ohms law would suggest otherwise but it doesnt really apply to servos, if you had a regular and HV servo pulling the same torque and the same speed then yeah the HV would draw less than the regular, but thats not a real life scenario.


This is something i have thought about when I first got hold of my CC Talon 90, it has an internal BEC rated at 9amp continous, 20amp peak delivered through a single servo connector?

The standard molex SL connector has been around a while, whilst perfectly adequate for the majority of applications maybe its starting to push it on the high power set ups. On servos individually its OK but maybe not so on BECs supplying the powerbus of your FBL with molex connectors. If your pushing an 800 sized heli on a HV set up your gonna be shifting quite a bit of current.

Saying that ive never heard of anyone melting their servo plugs