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I got this automatic antenna for a project, but the torque is a little too high. It runs on 12V. I've figured the way it works is, it knows to stop when the load increases to a certain point (i.e. something stops it from moving any more). It uses some digital circuitry to determine this.

Would it be possible to decrease the torque of the motor while retaining the properties of stopping when enough load is supplied? Would reducing the voltage be effective here?

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    \$\begingroup\$ It may also use a limit switch or rotary encoding sort of method. Have you tried blocking it's motion to ensure it detects the load? \$\endgroup\$ – Bort Nov 15 '17 at 19:24
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    \$\begingroup\$ I've blocked the motion at an arbitrary length to determine that's what will cause it to stop, but haven't measured things like current changes. In doing so, I noticed that there's some retry logic, as in, if it doesn't extend as fully as designed it will try 2 more times, and then stop. It's more sophisticated than I thought a power antenna could be. \$\endgroup\$ – BrDaHa Nov 15 '17 at 19:37
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Just too little information to write a real answer to this.

Reducing the voltage will indeed reduce the max current and speed of the motor that is driving this. However, if it is indeed current sensing to stop the drive if the antenna is obstructed, reducing the voltage too much will defeat that function.

Best way to find out is run it off a bench power supply, adjust the voltage down from 12v and see what happens. Of course, if you reduce it too much, it will not move at all.

What are you using it for anyway, I'm guessing not as intended.

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  • \$\begingroup\$ Yes, not using it as intended :) It's being used for automating opening and closing a chicken coop door. I'm trying to avoid breaking the coop, or unintentionally cutting a chicken in half. \$\endgroup\$ – BrDaHa Nov 15 '17 at 19:35
  • \$\begingroup\$ @BrDaHa may be interested in this cross-post then electronics.stackexchange.com/questions/331691/… \$\endgroup\$ – Trevor_G Nov 15 '17 at 19:39
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    \$\begingroup\$ @BrDaHa and this youtube.com/watch?v=OM8_4VTt-iI available from e-bay apparently \$\endgroup\$ – Trevor_G Nov 15 '17 at 19:42
  • \$\begingroup\$ Huh, that would be pretty nice, but would require significant modification to the existing coop structure. amazon.com/gp/product/B010PZWIJA/… \$\endgroup\$ – BrDaHa Nov 15 '17 at 19:51
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    \$\begingroup\$ @BrDaHa ya was just highlighting they use hospital bed actuators with a micro-switch for chicken slicer detection. alibaba.com/showroom/hospital-bed-linear-actuator.html May be more suited to your needs. \$\endgroup\$ – Trevor_G Nov 15 '17 at 19:54
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I remember having a broken power antenna on that model car. The motor probably draws 10A on start with max torque which can strip the plastic gears if the antenna is frozen ( in Winterpeg). Then drops to 1A or so at speed.

Reducing the start torque 50% would require adding a power resistor equal to the DCR motor resistance with a power rating of about 10W ceramic mounted to chassis for heatsink.

Perhaps you could elaborate the reason for excess torque being an issue. (Ice?) then you can use a series PTC rated less than 50% of 12V/DCR so that only a sustained stall would trip the current and resume when cool and unstuck, just like power windows.

https://www.digikey.com/products/en/circuit-protection/ptc-resettable-fuses/150?k=ptc

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  • \$\begingroup\$ Ah "Winterpeg".. I remember it well.... esp Portage and Main... \$\endgroup\$ – Trevor_G Nov 15 '17 at 20:08

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