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Spektrum TM-1000 - RPM sensor on brushless motor

Discussion in 'Transmitters & Receivers' started by ecruz64, Apr 26, 2013.

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  1. ecruz64

    ecruz64 New Member

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    Happy Friday Everyone!!

    I've been tinkering with my new TM1000 freshly installed into my Trex-450 and somethings not right with the rpm sensor. First, my heli is on the bench (blades off) and I have linear curves for throttle/pitch on my DX8. I spool her up and with less than 25% collective the rpm readout is over 22K. As I continue to give more throttle it eventually cuts out and the display reads "-----". Granted, I am a newbie and I have a lot to learn, but 22K is way to high for such little stick, right? Also why does it cut out (------)? I'm stumped.

    I installed per the instructions and soldered to the motor leads (blue/black).

    thoughts? Suggestions?

    thanks

    Ernie
     


  2. pvolcko

    pvolcko New Member

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    Depending on the motor kv and battery you're running that is about double (maybe a little over) what you'd expect on a linear throttle curve at 25%. Is there a setting for electric vs nitro rpm sensing that might cut the reading in half? Or a motor pole count entry that helps the TM-1000 or Tx scale the reading appropriately?

    - - - Updated - - -

    Also, it is cutting out because there is a 65k upper limit on the reading. You're probably hitting it around 2/3-3/4 stick.
     
  3. ecruz64

    ecruz64 New Member

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    Great question; unfortunately, it's one I don't have an answer too. The instruction that came with the tm1000 are pretty straight forward. I didn't see any tweaking options.
     
  4. pvolcko

    pvolcko New Member

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    There should be a pole count setting in the Tx on the RPM telemetry screen. Set it to 6, I believe, for those motors.

    - - - Updated - - -

    On the DX7s (and I expect on the DX8) the setting is on the telemetry setup screen in the heli setup area (same area you'd use to program a new model into the Tx). Goto the telemetry setup screen, select the RPM entry, then re-set the RPM entry, it will bring up another screen where you can enter the pole count, ratio settings (so it will give headspeed instead of raw motor shaft speed), etc.
     
  5. ecruz64

    ecruz64 New Member

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    Great suggestion, thank you! I'll give it a shot after work.
     
  6. ecruz64

    ecruz64 New Member

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    Confirmed. 6 poles! What should I set for ratios & how did you get that information?

    Thanks again!!
     
  7. Tony

    Tony Administrator Staff Member

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    If you set a ratio other than 1:1, then you will set it to show you the head speed, and not the motor speed. If you would like to read head speed (which is more important than motor speed on an electric), then divide your main gear by your pinion. This will give you a number as shown below.

    Lets say you are running a 14t pinion and a 150t main.

    150/14=10.714285

    You would round that number to 10.71 or 10.72 (dealers choice, but 71 is closer) Then set your gear ratio as close as you can get to 10.71:1
     
  8. Westy

    Westy LEGEND

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    ratios for gear ratio? to work out your rotor head speed? is that what you are asking?
     
  9. pvolcko

    pvolcko New Member

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    I got the pole info off align's site (had to zoom in on the performance graphs of the motor to see the pole count).

    Ratio should be set to pinion gear teeth divided by main gear teeth. Both the main gear and pinion gear tooth count should be in your heli manual or you can look on the parts (it is usually labeled on there somehow). I'm not sure if it is expecting a reduction ratio (will be fractional) or a gear advantage ratio (will be > 1) so you may have to play with it and see. Reduction ratio is what I described, divide pinion teeth by main gear teeth. Advantage ratio will flip the division values (or take the reduction ratio and divide it into 1).
     
  10. Tony

    Tony Administrator Staff Member

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    Yea westy, you can either set it to read the motor rpm (1:1) or you can set it to read the head rpm (10.71:1).
     
  11. Westy

    Westy LEGEND

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    ah .. is there anyway to govern head speed on an electric?
     
  12. Tony

    Tony Administrator Staff Member

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    Um, you need to divide main gear by pinion, not pinion by main gear. If you divide pinion by main gear, you get .09333
     
  13. Tony

    Tony Administrator Staff Member

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    Yup, You can use the governor in the Tx to hold it to a specific head speed.
     
  14. Westy

    Westy LEGEND

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    which Tx's support this? does the DX6-i or DX7-Se?
     
  15. Tony

    Tony Administrator Staff Member

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    Neither of those have telemetry. You need the 7s or the 8. It uses the telemetry module to tell the Tx what the heli is doing.
     
  16. ecruz64

    ecruz64 New Member

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    Wow! That would have taken me a while to figure out.

    Thanks guys, again, a HUGE help!!
     
  17. Tony

    Tony Administrator Staff Member

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    That is what we are here for. Each 450 has a different main gear. If I knew what heli model you had, I would have given you the exact ratio.
     
  18. pvolcko

    pvolcko New Member

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    That's what I would multiply the motor speed by to get head speed (and a factor of .85 or so to account for inefficiency) so that's the ratio I would normally calculate and use. :)

    As I said, divide that into 1 and you get the inverse ratio which is what was needed, apparently. I wasn't sure which one the Tx setup needed.
     
  19. Tony

    Tony Administrator Staff Member

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    Actually the Tx reads the exact rpm of the motor so there doesn't need to be an efficiency equation. It goes by the rpm of the motor, it's also a direct drive so if there is an accurate gear ratio, it can tell you within 100 rpm of what your head speed is. And it will display it on the Tx. I love the DX8 lmao.
     
  20. pvolcko

    pvolcko New Member

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    Good point on the efficiency. I'm used to working my head speed spreadsheet based on motor ratings. :)
     
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