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Servo booster and other RC queiries

Discussion in 'Robotics & Mechatronics' started by jpoopdog, Sep 10, 2013.

  1. jpoopdog

    jpoopdog Member

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    Hi,

    A while ago, at the dump recycling shop i scored on seperate days, for $5 at either time, a portable dvd player and a box with a bunch of old broken rc cars (parts from a nitro car and 3 electric chasis with parts still on), and the second time a 7" digital photo display, great condition plus a great condition 4ch medium sized rc helicopter with everything, only things wrong were 1 cell in the lipo battery was inflated, the other i tested is working totally fine strangely enough, also the gear driving one of the two propellors (2 sharing a single shaft) is completely flat on 25% of the gear so realisticly it would never fly, especially since it had no tail propellor that could possibly compensate.

    Anyway, with both of those, i got 2 high powered medium sized motors, 2 small servos, 2 large servos, a large brushed dc motor, 2 reversible ESC's 3 car chasis, 3 working 2ch receivers, 1 working 4ch receiver, 1 4ch helicopter AM or possibly FM (says fm but works on am receivers), working perfectly fine, 1 dismantled but possibly honkey dory (ok) 2ch pistol style remote which uses a board that is small and square and can easily transfer into any case, perfect for what i may have in store for it, and then mechanics wise i got a few parts here and there which can also be used, like about 5-6 sets of suspension steering sets, all in perfect condition, a differential drive which in the book is called a gearbox, which works and is presently already connected to the motor and other assorted rods and stuff.

    My goal is to hopefully build a decent car with all these parts. There are certainly enough, however the servos i have are quite old, or too small (they are japanese and look perhaps 10-20 years old, the chasis of the car was pcb fiberglass and hard a cast iron bullbar/bumper and wheels with actual detailed rims), so i aim to either rev up the power, or replace them with much larger servos.

    In either case building my own servo booster would be ideal, plus i dont like the idea of driving servos directly off the receiver, it just doesnt feel right, like running a motor directly off a 555 chip for PWM.

    ANyway, the servos are fairly standard, 3 wires, one white red and black in that order. How do i go about making a servo booster for them? im not fermiliar with how servos get their signals and power but its my understanding that the white wire is a PWM signal, and the red and black are power, in which case a booster would simply be an amplifier on the power input, right?
    otherwise, please tell me how i should amplify the power to the servo to operate it safely off the receiver with a little more juice or otherwise accommodate a much larger servo.
    Also, the servos and receivers that i have been able to get to work together so far are not from the same cars so i dont know if they are even supposed to be working together or not, ideally i want to avoid wrecking anything. Also this would would be used to possibly use the helicopter 4ch receiver on larger servos, the helicopters servos are quite tiny so im unsure about how compatible it might be with larger servos.



    So thats the servo question down, the next thing i wanted to ask was is it possible to push a receiver down/up two channels? specifically i want to use two 2 channel receivers together as a 4ch receiver, but they both use the same channels in the same frequency.
    I have quite a few receivers here but i will probably only end up using 1 that will permanently sit inside whatever project i use it in, leaving 2 free that i likely wouldnt use, unless of course they could be used together.
    so would it be a matter of changing the crystal? or altering a resistor/capacitor value or some other thing inside the receiver circuit? or is it just not practically possible? though i already have a 4ch receiver, i thought it might be a bit of fun to try and do that.

    Lastly, i want to hook up a 5-6v rail comming off the main battery which will be anywhere from 8-12v li-ion, that 5-6v rail would power any lights, the receiver and also be the power input for the servo booster if its required, so as not to use a seperate AA battery pack to power it, since thats just silly.

    How should i go about connecting a regulator up to the main battery, would a capacitor and diode be enough to protect it from any spikes and such from the motor?
    If i should use a specific regulator and diode, what do you recomend, also, what would be an ideal current range for the regulator to have, so as to ensure im ensuring that theres enough power for the receiver and servo and maybe then some? im not sure about how much your typical servo and receiver use, plus i have different receiver models here so it may vary slightly.

    Thankyou
     
  2. misterT

    misterT Well-Known Member Most Helpful Member

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    You can't boost the power buy feeding larger voltage to it. Most servos operate on 5V.. some servos has 6 Volt limit. Best you can do is to make sure there is enough current available for the servo. If the receiver can't supply enough current, then you need a voltage regulator that can deliver enough power. If you google "5V voltage regulator", you will get many results and options.

    Do the servos have any markings on it? Brand and model etc. Maybe they can tolerate 6V or more, but It is very risky to just try it.
     
  3. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    By "servo booster," I think you mean servo controller. To a limited extent the power of a servo can be increased ("boosted") by increasing the operating voltage from 4.8V nominal to 6V, Most modern servos will tolerate that change. Do your servos have any labels on them? Brand and number?

    As for controlling the servo, look up "servo tester" and you will get many hits. The analog circuits are often based on the 555 chip; digital circuits will use a microcontroller like a PIC12Fxxx or other brand. I assume you are more comfortable with analog, so here are two versions:

    http://home.cogeco.ca/~rpaisley4/xServoTest555.html (two 555's)
    http://www.555-timer-circuits.com/servo-tester.html (single 555)

    You have to go way back to find servos and receivers that won't work together. Just be sure the connections are proper. The standard order of wires, Signal, V+(red), and Ground (black) was not followed by all manufacturers until relatively recently. Airtronics and some others had Ground as the center wire. Those servos will be burned out, if you make the center wire V+. Remember, the servo draws almost no current with the signal wire. Its supply current is the red and black (in your case) wires. Remember too, the color codes may be slightly different for different brands. For example, instead of black, you may have brown, and instead of white, it may be orange-yellow or blue, i.e., some color that is not black, brown, or red.

    It is not practical to use two, 2-channel receivers as a 4-channel receiver without some major rework. You would have to go into the receiver, find the decoder chip and see if there are other channels. Some smaller receivers simply bring out fewer channels from that chip than it is capable of providing. So, there is a chance your 2-channel receiver is really a 4-channel with only two channels brought out, but I seriously doubt it.

    John
     
  4. dave

    Dave New Member

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  5. jpoopdog

    jpoopdog Member

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    Well that makes sense, with the receivers, if you say it wont work ill take your word for it. also the circuitry is a tab too tiny for me to mess around with, so ill just buy another 4ch receiver should i need it.

    However, about the booster, i just mean to supply more current so that a larger servo, would have no issue running, by booster i just mean to put a transistor on the power in running through a voltage regulator with a current specific to the useage of said servo should my receiver not be able to supply enough current.
    One day i plan on making a large petrol powered rc car, which will be quite large, using an actual petrol engine 25-50cc i think, but i could be wrong, anyway, itle need a fairly large servo to turn the wheels, which would probably be out of range for these small servos.
    Also, two of the 3 2ch receivers have no markings or numbers anywhere on them so i cant look up anything about them. So just in case they wont work and i wind up having to use them i want to know that i can have them drive a transistor driving the servo, again, within its operational range, just incase what they have now isnt enough for potentially larger servos i may use in the future , i dont know if i will need them, but still, better to have them working at 100% than 50%.
     
  6. misterT

    misterT Well-Known Member Most Helpful Member

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  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    If you need more current for the servo(s), which is not uncommon, the best solution is to use a switching regulator. Consider the example of a 12-V Li-ion battery powering six, large servos. If each servo took 1A at 6V under load, a linear regulator would need to dissipate 36W of heat. Servos under load will draw a lot more current than when just resting.

    I happen to use Castle Creations switching regulator and ESC to run 6 servos and a motor from a 3S LiPo pack. There are, of course, other brands, including some that are quite inexpensive from Hobby King (China). I think you can find a cheaper switching regulator than you can make.

    John
     
  8. jpoopdog

    jpoopdog Member

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    Oh a switching regulator, ill give that a look thanks, those are essentially doing the same thing a speed controller does isnt it.
     
  9. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I don't think I would go that far. A speed controller, even the older ones, gives PWM power to the motor. That may be 3-phase pulsed for a brushless DC motor. A regulator will have filtering and smoothing so the power delivered is DC, not AC or pulsed.

    John
     
  10. misterT

    misterT Well-Known Member Most Helpful Member

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    No.. switching regulator does what ordinary linear regulator does. It just does it more efficiently.

    EDIT: Are we talking about regulators or amplifiers? There is a difference.
     
  11. alec_t

    alec_t Well-Known Member Most Helpful Member

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    It's the power supply/battery, not the receiver, which supplies the current drawn by the servo's motor. The receiver sources/sinks only the tiny current needed to control the switching of that motor current.
    You won't be able to boost the power of a servo significantly, but you could use two servos linked together mechanically and controlled in parallel to double the power available to move something.
     

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