Rc Brushless motor setup in a v3 gearbox.

Discussion in 'Gun Building, Modifications & Repairs' started by Ben3721, Oct 4, 2020.

  1. aotsukisho

    aotsukisho Well-Known Member

    490
    299
    You're better off using 3.5-3.7v per cell for calculations, both for a nominal voltage average rps and also to account for voltage sag when motor is running. 4.2v/cell will give you theoretical maximum RPS, which is normally unattainable even on a power supply due to frictional losses unless your motor's KV is out of spec.

    Yes KV makes it way easier to calculate based on different voltage configurations. I don't know why brush motors aren't advertised in a similar way.

    You are correct, the pot 'ends' are a fixed resistance that does not change, and the wiper simply touches the track and the appropriate resistance is 'seen' by it. Example a 100k pot, left and right pins will always measure 100k but the wiper being in the middle will measure 50k on either side. Move the wiper to left 25% and you'll see left-mid measure 25k and mid-right measure 75k. (When I first started working with electronics I was surprised to discover this as well, I thought the two 'ends' were isolated)

    Hence my 'trick' is to use an SPDT switch with resistors matching the total pot resistance to simulate the wiper moving, as the switch in either position will short out one of the resistors.

    [​IMG]

    From my Nerf Stryfe build documentation, but the theory is the same as it was used to run two brushless outrunners as dart flywheels.



    I have not run into problems with the three servo testers I've modified this way, I'm assuming they use the pot as a voltage divider so the resistor values can be flexible (ie 5k you can substitute 4.7k)

    You can adjust drag brake for that, it's 'softer' than active braking and because it is regenerative it will be better than letting the geartrain bounce off of the spring and waste its energy. Programming card highly recommended

    Looking forward to seeing progress!
     
    Last edited: Oct 20, 2020
    Ben3721 likes this.
  2. Ben3721

    Ben3721 Active Member

    327
    175
    So I'm starting to see heat management will be factor in my build. I think I may attempt to transfer heat from the esc directly into the v3 gearbox top, the gearbox should remain fairly cool as its moving an enormous amount of air. I want to find some sort of thermal tape that has one side with an adhesive on a thin plate on the esc (to keep it sealed still) then on the backside a short wide spring to keep it pushed down when the dust cover is on. Allowing heat transfer while keeping the electronics modular. I wish the motor axle was on both sides of the motor, id add a fan on the back with some vent holes in the grip bottom. Some outrunners have that built in. But not inrunners.

    I wonder what temperature the esc and motor can tolerate, and if it can run longer than a brushed setup, enough for an intense firefight. Maybe a few seconds of auto bursts at 35rps, and 400-600 shots in semi non stop.
     

  3. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    Ready to solder. If running power to tester from ESC and only running wires to trigger contacts how would my relay/tester wiring differ from your pictures if i don’t care about using the POT for a variable rate. IMG_1603229646.999586.jpg
     
  4. Ben3721

    Ben3721 Active Member

    327
    175
    You need that switch stuck on Manual and the potentiometer removed entirely if thats your intention to do a 0%-100% switch without variable speed. Your relays common leg (the leg between the two electromagnet legs) would be wired to the middle hole, then the two other legs alone on the relay would be wired to the other two potentiometer side holes, the one that's the closed side would be wired to the 0% side and the open side of the relay would be wired to the 100% side, meaning it needs powered to turn on.

    Then the two legs of the relay that power the electromagnet would need two long pairs of thin wire, one that passes in and out without being cut, then the second one needs cut and wired to the electromagnet. This loop of wires creates 4 wires once your done, two go to the trigger, two go to a 12v power source.

    If the esc has its neutral at 50% this setup will not work.

    Here is an exposed relay that your using. It had no markings so I broke one to see inside.
    [​IMG]
    Top plate is the common, its leg is between the electromagnet legs

    [​IMG]
    The photo isn't super clear, above the right leg is the one closed, and the left is the one open, I repeat its touched the top contact without power.


    [​IMG]
    More photos of the common leg and the two electromagnet legs.
     
    Last edited: Oct 20, 2020
  5. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    The fog is lifting! My relay is 5v can I drawl my power from the board on go directly off the ESC + & - pins which is 5v coming from the ESC internal BEC?
    Oh Yeah I just opened one of my relays clear as day now!
     
  6. aotsukisho

    aotsukisho Well-Known Member

    490
    299
    Keep them under 160°F, actual thermal limits are higher but not all components receive the same mount of heatsinking. Do note that the human threshold for pain is around 130°F, so if your components are getting too hot to touch you will need an IR thermometer. Take readings off of a matte surface or else surface reflection may screw up your readings. I've heard of people putting electrical tape on brushless motors to act as a temp reading patch.

    upload_2020-10-20_12-31-51.png
    My suggestion, use the bottom for standard AEG trigger installation with relay. Battery negative goes to switch, other end of switch goes to relay coil, other end of relay coil goes to battery positive. Even 2s lipo should be able to flip the relay, most of the 12v relays I've used trigger all the way down to 5-6v.

    My handwriting is borderline illegible so Rp = resistor equal to full value of the pot. Circuit will spoof the pot being all the way counterclockwise when at rest, and all the way right when trigger is pulled. Desolder the pot, and put the wires into the PCB as shown. Circuit behavior is not guaranteed if pot remains in. Your relay might have its pinout silkscreened onto the side, if not you need to find the part number and look at the datasheet.

    Would not advise doing this, the resistors are there as a current-limiting voltage divider. Semiconductors do not follow Ohm's Law and may need external components to prevent burning out. My circuit keeps the voltage divider intact for maximum reliability as we do not know how the circuit was designed and what safety measures it has.

    Yes you can use the 5/6v feed off the BEC to power the relay. In the above example that would be negative and positive from the servo tester or ESC rather than directly to the battery.
     
  7. Ben3721

    Ben3721 Active Member

    327
    175
    That's the blue relay its 12v I'm pretty sure the black one was 5v. It won't work on 5v if it is the 12v.
     
  8. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    POT is out taking this one step at a time. IMG_0571.jpg
     
    aotsukisho likes this.
  9. Ben3721

    Ben3721 Active Member

    327
    175
    ignore my comment about the 12v vs 5v, seems you got a different brand one with different coloring. The inside is likely identical
     
  10. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    it’s a 5 volt here is my diagram blue ink is wire. IMG_1603237046.604679.jpg IMG_1603237111.275199.jpg
     
  11. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    YeeeeHaaaa It works all the credit goes to you guys will do video. IMG_1603242597.089189.jpg
     
  12. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    Will be testing it today in the gun! The really cool thing about this ESC is the data logging ability and the ability to program it in so many ways. I will be able to look at the logging after a string of firing and see amps watts ESC temperature RPMs and voltage. The only thing i worry a bit about is a runaway gun should the relay malfunction. Am going to install a cut off using the AUX cable from the ESC for that. Should have some test fires by lunch.
     
    Last edited: Oct 21, 2020
  13. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    Partial success the gun fires! However the motor struggles to start at the beginning but then goes and fires with no problem. Full auto is fine once the motor is going. Nothing getting hot and only pulling 11amps good grief this ESC is way overkill! I have tried everything in the programming to get the motor to immediately start smoothly changed timing pwm everything to no avail...it jitters for about a second then goes
    BUT it fires IMG_0573.jpg
     
    -Spitfire- and Gray. like this.
  14. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    Just tried firing it with 11.1 3S Lipo and it struggles to get started much longer but Holy Cow after it goes the rate of fire is STUPID. LOVE IT! I think what (aotsukisko) said way back on page 1 of this thread is bearing out...even with hard start (100%) in the program it is not hard enough for this gearbox and needs a totally different algorithm in the start up programming. There are some open source ESC's out there...in Europe...I have an RC Plane friend in England who fiddles with ESC programming....I might drop him a line;)

    Amps with 3S lipo 21.8......

    Without a way to DIG into the ESC Programming we might be dead in the water:(
     
    Last edited: Oct 21, 2020
    -Spitfire- and aotsukisho like this.
  15. aotsukisho

    aotsukisho Well-Known Member

    490
    299
    OJH you might want to see if you can up/downgrade the firmware of the ESC through Castle Link, some firmwares add or remove features and Castle's algorithms do change.
     
  16. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    I might contact Castle...also I contacted a European Open Source ESC guy...hopefully he will recontact me. Was thinking maybe Robot ESC's would give us what we need???
     
  17. Ben3721

    Ben3721 Active Member

    327
    175
    I'm wondering if my setup with the high speed motor and high torque gearset will have this issue... ill know in a few days hopefully. I noticed the same thing when trying to run it at half power on a 13:1 gearset.

    Would a sensored brushless have a better start up?
     
  18. aotsukisho

    aotsukisho Well-Known Member

    490
    299
    Very much so. Cogging, the stumbling the motor does when it starts moving, on startup is almost nonexistent but it's still up to the ESC software how quick power 'ramps up' to 100% after the motor gets moving. Cogging also gets worse on how much load is put on the brushless motor at rest, so make sure braking is high enough to halt the geartrain before piston pickup starts again.

    This is the primary reason why I don't think brushless motors make brush motors obsolete, their complexity and difficulty moving slowly aren't good fits for some applications.
     
  19. Oldjarhead

    Oldjarhead Member

    40
    31
    Thurmont
    They make two brushless motors for airsoft that I have found.
    https://www.evike.com/products/77716/
    https://www.evike.com/products/20022/
    They have built in ESC's...expensive, yes and no because they are the motor and ESC all rolled into one. Several of my High Performance Hotliners have motors and ESC's (200amp) that together cost 700....but, they perform like you would not believe. Those planes have to the room to mount them and the 8S lipos that power them.
    I think the issue is no one is making an ESC that is Airsoft specific. The problem is there is so little room in most platforms for it. The M14 DMR stock has the room and some heavy weapons might have the room but you will be hard pressed to stuff it in anything else. If it wasn't for HPA...brushless setups would be the norm by now...but nothing is forcing the industry in that direction. RC CARS/TRUCKS finally figured it out why is airsoft so far behind.