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Sep 16, 2019, 01:27 PM
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Wanted

Winch Resistor


I have a winch I purchased on the groups a little while back. I believe it was set up for F3B. I'd like (kinda need) to use it for F3J team selects. I'll need to get one of those variable resistors. Does anyone have a line on one? I'd really like to get it ASAP for next weekend's practice.


Thanks!


Mike Gardner
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Sep 17, 2019, 07:14 AM
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Here's some pictures of the winch. It has the quick disconnects for the batter so I don't think I can use a resistor between the battery and terminals. There is a plate going from the selonoid to the motor on the positive side. Maybe changing that could provide different resistance values. I need to make sure that I can adjust it at a contest when it is tested. How is this tested?
Sep 17, 2019, 08:20 AM
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Hi Mike jr

You may want to do some research on current shunts, I believe there's formulas on length of shunt, based on cross sectional area. Stainless is a good material

Surely you could bend one up once you find the base of reference for testing the power loss across the shunt.

whacker
in the wet Waughs River Valley
Sep 17, 2019, 11:30 AM
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Quote:
Originally Posted by mikejr83
Here's some pictures of the winch. It has the quick disconnects for the batter so I don't think I can use a resistor between the battery and terminals. There is a plate going from the selonoid to the motor on the positive side. Maybe changing that could provide different resistance values. I need to make sure that I can adjust it at a contest when it is tested. How is this tested?
Mike, that bar between the solenoid and the motor is the shunt. You would adjust that. Mike Lachowski just helped me test my winch this weekend. You need the whole thing hooked up and then you need to arrest the spool. I used by hands but you could use a clamp as well. You'll need to measure the voltage of the battery while the system is idle then you need the voltage and current of the system after it's activated (the FAI book says 30 milliseconds after you hit the pedal). There is a specific testing box used but you could test your own using a volt meter and and amp meter. Minimum resistance is 23 milliohms.

Take a look at the FAI sporting code for F3B, the explanation is very good.

Hope that helps. As long as you can adjust it, you'll be okay, you can adjust the winch at TS.
Sep 17, 2019, 11:31 AM
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I built a prototype F3B winch years ago and documented it here on RCG. The resistor used Manganin rods that could be slid in or out to change the resistance.
The resistance was tested by using an old "Der Windentester" electronic measuring device but nowadays they use a clamp OHM meter instead. Not sure which one but there might be more info in my RCG post here:

https://www.rcgroups.com/forums/show...=usa+f3b+winch

I never made any others as too many F3B guys wanted very individual specific things and that would have been a nightmare to produce them as individual winches. They all wanted it to be like an OBER but that was already available.

Manganin is hard to find. I had to order it overseas. There may be other materials not affected by temperature variances. Manganin is the best material for this.
Last edited by V1VrV2; Sep 17, 2019 at 11:43 AM.
Sep 17, 2019, 12:28 PM
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I have a little 1mm thick manganin sheet around. Enough for another 3 or 4 strips suitable for use as a resistor if it is a normal Bosch motor and with a normal battery, not a really high CCA, low resistance battery.

Last Bernie Sizer winch I tested that didn't have a resistor on it was in the 20 milliohm range with a bigger battery. Great for launches...... But far from legal.

The Ober resistor material is four 3mm rods. So for resistor length, a 28mm wide strip of 1mm is close to the four rods in ohm's/mm. The ober also has a slider and other brass pieces. So all the places you have metal to metal contact, you add a little resistance. The obers when adjusted usually end up around 2.5 inches between brass pieces that clamp on the rods.

The sheet I have is left over from when I built a bunch of winches a long time ago. It is crazy expensive if you just wanted to order enough for one resistor from Goodfellow. About $200 if you wanted just one. If you wanted enough for 20, then maybe it would be $25 a resistor. Or maybe there is some cheap source in China.

Probably the easiest to build would be some of the 8mm rod since then you only have one rod to adjust. It just reduces the surface area for heat dissipation.

The low budget and less efficient solution is to use stainless steel. Resistance goes up as it heats up.

The resistor will get very hot on a longer launch. It might be only 2 to 3 milliohms but when you put a few hundred amps through that. it gets toasty.
Sep 17, 2019, 12:36 PM
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Quote:
Originally Posted by Bmwjoon
Mike, that bar between the solenoid and the motor is the shunt. You would adjust that. Mike Lachowski just helped me test my winch this weekend. You need the whole thing hooked up and then you need to arrest the spool. I used by hands but you could use a clamp as well. You'll need to measure the voltage of the battery while the system is idle then you need the voltage and current of the system after it's activated (the FAI book says 30 milliseconds after you hit the pedal). There is a specific testing box used but you could test your own using a volt meter and and amp meter. Minimum resistance is 23 milliohms.

Take a look at the FAI sporting code for F3B, the explanation is very good.

Hope that helps. As long as you can adjust it, you'll be okay, you can adjust the winch at TS.
It is in the F3j rules too.

https://www.fai.org/sites/default/fi...soaring_19.pdf See 5.6.8.2
It is 300ms, not 30.

Don't forget the general rules
https://www.fai.org/sites/default/fi...les_19v2_0.pdf
Sep 17, 2019, 02:34 PM
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Quote:
Originally Posted by mlachow
It is in the F3j rules too.

https://www.fai.org/sites/default/fi...soaring_19.pdf See 5.6.8.2
It is 300ms, not 30.

Don't forget the general rules
https://www.fai.org/sites/default/fi...les_19v2_0.pdf
Yess 300 !

Mike you are the winch guru! I actually learned a lot, thankyou!

Joon
Sep 17, 2019, 04:39 PM
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V1VrV2's Avatar

Repost to the sailplane forums?


I think this post deserves a dual post to the sailplane forums as its not discussed at all. BUT the F3B winch testing and requirements certainly deserve attention every so often. It is, after all, the formula 1 of sailplanes...

Sep 17, 2019, 07:35 PM
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Quote:
Originally Posted by V1VrV2
I think this post deserves a dual post to the sailplane forums as its not discussed at all. BUT the F3B winch testing and requirements certainly deserve attention every so often. It is, after all, the formula 1 of sailplanes...


Done: https://www.rcgroups.com/forums/show...s#post42761433


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