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Jolt & friends - Team Overkill - NSW
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Valen
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Joined: 07 Jul 2004
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Location: Sydney


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Probably the fet body diodes conducting.
If you go in reverse the other low side fets will probably heat.

Are you running that into the resistor or the mag motor for your test?

If you use the spin controller (one direction only) you can probably reduce the heat generated in the electronics bay with some diodes across the motor.

What is the spec on that cap? (part number for the one you have would do fine)

Try element 14 for parts btw, much cheaper for shipping generally.
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Post Tue Sep 02, 2014 11:26 am 
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Nick
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The last test was with the Mag motor, the resistor would have vaporised Smile. Here are the capacitor specs: http://www.digikey.com/product-detail/en/EEU-FM1V122L/P12406-ND/613767 . Its physically a bit larger than the original and a higher capacitance too.

How about adding a bi-directional TVS diode across the ESC output? I have some rated at 28V, which should clip spikes without shorting the ESC at normal voltages.
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Post Tue Sep 02, 2014 1:48 pm 
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Valen
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Nah its the recalculation current, the body diodes are going to have like .6-1 volt across them at whatever amperage.
Putting "real" diodes in will just shift some of that out of the fets.

TVS diode should never do anything, wouldn't hurt, but really shouldn't be needed.
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Post Tue Sep 02, 2014 4:48 pm 
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Knightrous
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Joined: 15 Jun 2004
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Location: NSW


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quote:
Originally posted by Knightrous:
quote:
Originally posted by Nick:
What brushed motor size are they equivalent to?


They are a 600/700 series equivalents (42mm). They are advertised as 1/8th RC motors, but voltage ratings are specified as 3S to 12S LiPol and 2600w peak power.


Had these arrive today...

Will see if I can test them on the weekend before packing them up to go to Sydney Razz
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Last edited by Knightrous on Wed Sep 03, 2014 12:54 pm; edited 1 time in total

Post Wed Sep 03, 2014 11:57 am 
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Nick
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Probable problem, reasonable resolution?

After upgrading a Victor ESC to drive Scissorhand's weapon, I ran into a control problem that should have been obvious Embarassed. Previous controllers were off at 0% drive on their radio channel and switched on at 50%, which worked well with fail-safing. The Victor 885 is 'off' at 50% (IE the neutral position) and anything else is driving the Mag motor in one direction or another.

The transmitter doesn't like the fail-safe position to be 50% so I came up with a solution: if the motor is connected between battery ground and the positive ESC motor terminal, the motor starts from 50% and anything less drives the disconnected side of the H bridge and the motor can't spin. That makes the fail-safe actually safe and works on the test bench - the question is whether it will work as well in real life?

The Victor spin controller would be an easier & better solution but 3 days of searching have not located it. Murphy's Law means that it won't be found until mid October.
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Post Wed Sep 03, 2014 8:33 pm 
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Valen
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can you change which channel you are doing your weapon on?
I'm guessing you are using the throttle channel and its having a hissy fit.
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Post Thu Sep 04, 2014 8:54 pm 
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MikeNCR



Joined: 05 Jan 2012
Posts: 54
Location: Norcross, GA USA


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I got around that issue on Moros by switching the weapon from the throttle channel to the rudder channel, so left spun one direction, right spun the other.

Post Thu Sep 04, 2014 10:18 pm 
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Nick
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I am using a pistol-grip radio with the weapon controlled by a button on the AUX channel - its not as versatile as using a stick radio with plenty of spare analogue channels Sad. Its OK though, I have a plan C in the works.
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Post Fri Sep 05, 2014 1:55 pm 
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Nick
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Mag motor control, Plan C:

Firstly, thanks to everyone for the 600,000+ page views, I really appreciate all the help and feedback from the whole international combot crew! Very Happy

I got the Victor 885 working on the 3rd radio channel with fail-safing; its wired like it is a spin controller, but with just three FETs taking all the load. I think I can do better with a custom controller using a small Robotpower ESC to drive a bank of high power FETs:



The FETs should be good for over 150A and I an always add 5th FET on a longer heatsink. Its not a new idea, but with everything I learned from the Victor repairs, I can get this working properly. This will give 50% to 100% proportional control and just needs some breadboard to hold the gate resistors.
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Post Fri Sep 05, 2014 8:56 pm 
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Valen
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Invest in some kapton tape, I'd hate to see it blow up due to a short.
Also make sure to keep your gate drive connections short.
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Post Fri Sep 05, 2014 10:07 pm 
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miles&Jules
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Hey Nick whats that orange stuff your using for your belt called and what size is it?
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Post Sat Sep 06, 2014 12:02 am 
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Nick
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The belt comes from Fenner drives in the US and is called Eagle Belt: http://www.fennerdrives.com/reinforced-belting/_/Eagle-Orange-85-Reinforced-Vee/ . I am using the smaller Z sized belt and so far, its doing very well. I had to buy a huge roll of the stuff, so there is plenty spare if you want some.
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Post Sat Sep 06, 2014 8:05 pm 
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Mouldy



Joined: 10 Aug 2011
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Nick did you check out the fet board sam smith made for NST? Tiny considering the current draw its capable of. Might be worth asking him for some pics... ill send him a link to this thread if you like?

Post Sat Sep 06, 2014 11:46 pm 
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Nick
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I didn't see that yet; it would be really interesting if any info is available!
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Post Sat Sep 06, 2014 11:51 pm 
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miles&Jules
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ah cool Nick will see if the local bearing place has any urethane belt…if not might take you up on that. Very Happy
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Post Sun Sep 07, 2014 1:29 am 
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