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Author Topic: Help Wanted  (Read 726 times)

mk1

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Help Wanted
« on: September 11, 2019, 11:56:57 PM »

 Hi all I am after a bit of information on Brushless electrics etc as I am not very good with Brushless items Thanks in advance.
1         I am building a boat with 2 brushless motors with speed controllers what I want to know is can I use NiMH batteries with a brushless motor and ESC instead of Lipo ones as I donít want to have to buy Lipo batteries.
2          Can I use a Planet 5 controller with brushless motors and ESC. The other thing is would I have to use either a Analog or Digital servo with my Planet 5 controllerThanks John
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Stan

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Re: Help Wanted
« Reply #1 on: September 12, 2019, 07:19:30 AM »

Hi Mk 1 simple answer yes to both questions. Not sure about your servo but I am sure a servo is a servo plug it in and try it


Stan
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imsinking

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Re: Help Wanted
« Reply #2 on: September 12, 2019, 09:19:47 AM »

Yes indeed to all, be aware that a brushless ESC will be set to LIPO op's by default, in other words it will cut power if the battery strength is indicating low (which NiHm batteries will do ) you need to get ESC's with a programming card to set the cut off point to 'no protection' if your using NiHm's , as I found out  :embarrassed:  , also I couldn't get a Digital servo to work on a planet 2.4 , stick with analogue there cheaper .
Bill

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john44

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Re: Help Wanted
« Reply #3 on: September 12, 2019, 10:29:28 AM »

I agree with the above, I had a problem with the esc,s cutting out when using 7.2 Nimh I changed
to 8.4 Nimh and not had a problem since.


John
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malcolmfrary

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Re: Help Wanted
« Reply #4 on: September 12, 2019, 10:47:03 AM »


NiMH will stand being discharged to a much lower voltage than LiPo, so don't need the low voltage protection that LiPo do.  As long as the NiMH can supply the current demanded, no problems.  On an ESc with LiPo protecion being run on NiMH, a sudden heavy load might well drop the voltage enough to trip the protection.
The bit of circuit in anything that plugs into a radio should be looking for the same type of signal, and before everything was a little computer, such was the case.  It mostly still is, but designers are creeping what they think of as cleverness into their systems.  Any servo gets its power via (usually) its red and black or brown wires, and its control signal via the white or yellow wire and the black or brown wire.  If a servo wants a lot more power than the black or brown wire can deliver, odd things happen to the signal - digital servos generally want more power than their analog equivalents.  In boats, there really is no need for them.
When designers are given a permitted range of parameters to play with, they have the unfortunate tendency, rather than aiming for the center of the range of parameters, to go for one end of the limits or the other, usually to keep costs down.  Thats OK until an item aiming at one end of the limits runs into one aimed at the other end.
Brushless motors have the reputation that they do demand much higher instantaneous current than brushed motors, but can be more economical with power overall.  This means that the system, which includes battery, wiring and ESC, has to be able to deliver the peak current demanded without dropping the supply voltage enough to mess with the timing circuits, which are still as analog as it gets even if the label says "digital".
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Stan

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Re: Help Wanted
« Reply #5 on: September 12, 2019, 11:34:33 AM »

Simple answer buy M tronicks b/less speed controllers works out everything for you.No need for a programming card referance the servo question I have checked with a supplier of servo  should be ok but it is not wise to mix. I was bought a cheap brushless controller got sick it bleeping while setting up  finally it went in the bin. But you pays your money and makes your choice.




Stan
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JimG

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Re: Help Wanted
« Reply #6 on: September 12, 2019, 01:07:21 PM »

While standard digital servo will probably work with the planet Rx there are digital servos which need a faster signal rate which is provided by some high end receivers, these are not happy on standard receivers. The higher current needs of a digital servo is not generally a problem as the +ve and -ve connections are linked straight to the battery input and the circuit tracks can take a higher current than you might expect. The problem is generally where the power comes from a BEC which cannot provide the current needed so the voltage drops under load. As for whether digital is needed or not they do give better precision and hold their position better under load, I have seen cases on aircraft where standard servos were replaced by the equivalent digital and the movement was reduced as they did not blow back at the maximum movement.
Jim
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DaveM

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Re: Help Wanted
« Reply #7 on: September 12, 2019, 03:02:59 PM »

The problem is, Jim, that nowhere will you find that information either in the servo specs or the web pages for the manufacturer. I've now tried three different brands of 'digital' servo - all using separate battery packs for the receiver rather than a BEC speed controller - and they've all trembled and dithered horribly, even while 'resting' at neutral. I'd hardly regard my Hitec Aurora 9 or Optic 6 as low-end gear, so I gave digital servos up as a bad job and not really necessary for the tasks in hand.
DaveM
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mk1

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Re: Help Wanted
« Reply #8 on: September 12, 2019, 11:40:26 PM »

Hi thanks to all that have replied I thing I got the answers I wanted.
John
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JimG

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Re: Help Wanted
« Reply #9 on: September 13, 2019, 01:17:07 PM »

The problem is, Jim, that nowhere will you find that information either in the servo specs or the web pages for the manufacturer. I've now tried three different brands of 'digital' servo - all using separate battery packs for the receiver rather than a BEC speed controller - and they've all trembled and dithered horribly, even while 'resting' at neutral. I'd hardly regard my Hitec Aurora 9 or Optic 6 as low-end gear, so I gave digital servos up as a bad job and not really necessary for the tasks in hand.
DaveM
Rather surprised as I use Hitec (now Aurora 9X Tx) for aircraft and have used digital servos with both Optima and Minima receivers without a problem. In fact many ARTF foamies now come with digital servos as standard and these work well even though they are cheap servos. Mostly used with a BEC ESC although I make sure the BEC is capable of driving the servos.
Jim
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malcolmfrary

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Re: Help Wanted
« Reply #10 on: September 13, 2019, 06:28:44 PM »

When talking about digital positioning, it helps to know the sample depth - how many bits does each byte contain?  The bigger the sample depth, ie the more bits in the byte, the smaller the steps. 
Marketing people constantly tell us, totally inaccurately, that digital is more accurate than analog.  It isn't, but it does give a very constant level of inaccuracy which gets progressively smaller as the sample depth increases.  In audio, it is called "quantising distortion", and takes the form of a low level background random hiss a lot like white noise where the steps don't quite match what is wanted.
I am pretty sure that in the vast majority of servos, the sensor is still a pot.  That is as analog as you ever get, but when that analog voltage gets rendered into a digital value, it is highly unlikely to be an exact match.  As a result, you are likely to see a servo that is between numbers having a good dither between one and the other, probably at frame rate.  Smaller steps reduce this.  More cunning software might eliminate it.

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