Revision 1.3


Per-Olov Sjöholm

peo_s AT incedo DOT org


Revision 1.3 – 2009-05-09 – Added extra comment about CF vs Alu boom

Revision 1.2 – 2009-05-09 – Added info about extra resistor against short circuit. Added info about boom case in metal, Extra comment in the ending comment section

Revision 1.1 - 2009-05-07 – Translated to English

Revision 1.0 - 2008-09-14 – First revision (Swedish)


This document also exists as a PDF here: http://www.incedo.eu/~sjoholmp/helis/t-rex500-anti-static-modification/t-rex_500_and_the_anti_static_problem.pdf






At the end of the summer 2008 my friend and me switched our T-rex 450SEv2:s against T-rex 500:s. My friend was (lucky me) airborne before me. After just a few flights he got a ”brown out” and crashed hard. After some searched (black belt in Google searches) we saw that many people had this problem. So after we had solved all issues I decided to write down what we did to solve the problem and a few other ”nice to know” things in this matter. This document was first published in Swedish in September 2008. The Swedish version will no longer exist, as this translated one will have some updates that the Swedish version doesn’t have. Hopefully you can save your self some time and avoid spending the amount of time we have spend in this matter, which is a lot.





Static problems that can cause "brown outs" and a reboot of the receiver with a crash as the consequence seems to be a bigger problem on the T-rex 500 than on other helicopters.


Possible causes could be: The tail boom is to tight compared to other helicopters, which leads to the fact that the belt is very close to the boom and therefore easier build up electrical charge that could cause electrical problems. Another thing could be that the rear and front belt pulley is by default mounted in plastic cases that isolates the pulleys more from each other. This could then easier build up potential and in the end easier cause an electrical high voltage problem. The well-known Finless mention in a forum that electrical problems often decreases as the size of the helicopter goes up. This as the electronic parts no longer are so close to each other and to the pulleys, main gear etc that generates static electricity. To change from a belt driven system to the new "torque tube" decreases static electricity in the helicopter. I have however seen posts in forums (but very few) that states that they have had so called ”brown outs” even though they use the "torque tube". You should be aware of the fact that the main gear in nylon on _all_ helicopters _always_ generates _more_ static electricity than the tail with the belt drive (I have measured the static electricity on a couple of helicopters). And you don't exchange the main gear when you go over to the ”torque tube”.



Do you want to check the static electric yourself? I am sure you have seen this tool on youtube... In Sweden it can be bought at Clas Ohlson http://www.clasohlson.se/Product/Product.aspx?id=88598217








Ok... The people that have problem then....? Well... These modifications works perfect:



Alternative 1:


Use silicon spray on the pulleys, belt and the main gear on a regular basis. Some people claims that the gears and pulley will then suck up dirt and shorten the life of gears, belt and bearings. I did however not have any problems with my earlier T-rex 450SEv2 when looking at the parts in a magnifying glass after 50+ flights. The bearings were also still tight and perfect after _many_ flights. Draw your own conclusions....



Regarding silicon spray:

Use silicon spray and not antistatic spray. It simply seem that silicon spray is better against antistatic in the helicopters... Sounds weird...But I have done my own test with the above mention anti static measuring tool. The test have been done with Teslanol antistatic spray (art no: 18309) http://www.kjell.com/?item=18309 and Teslanol silicon spray (art no: 18318) http://www.kjell.com/?item=18318. The silicon spray is simply better than the anti static spray!



If you do not like alternative 1 above, you could go for alternative 2 below...


Alternativ 2:


Do the anti static modification as stated below.


# 1 # Switch to the metal tail unit and ground it to the boom


Buy the metal tail unit and use a piece of sandpaper or any tool of your choice to remove the pain/varnish from the surface for best electrical contact. DO NOT CHANGE TO CERAMIC BEARINGS in the tail case as the connectivity between the pulley and the tail case is lost (measure with an ohm meter or similar).  Also… remove the paint/varnish from the boom where it touches the tail case. See the pictures.



You could still use a plastic original tail case and modify it in the same way as the boom case with a small cable (see boom case pictures modification further down)












# 2 # Make sure that the boom in the boom case is grounded on to the front pulley and the motor mount.


Ground the front pulley against the boom through the boom case. Then ground the boom through the boom case further on to the motor mount.


I made two small ditches with my dremel for the cables in the boom case. I put some tin on the cable ends and glued them with CA into the milled ditches in the boom case. By doing this I do not have to think about this modification if I have to open the boom case.



Copter-X 500 has this boom case in aluminum. By using this instead of the original plastic you can don the modification of the boom case as easy as for the metal tail unit. But do not forget to use an ohmmeter or similar to check the connectivity. Its part number is CX500-03-08 and can be found at http://www.ehirobo.com/shop/product_info.php?cPath=173_236&products_id=6219








# 3 # Also ground the ESC ( - ) against the motor mount


Let the cable from the boom case and the cable from the ESC minus meet at the same spot on the motor mount. Note that you have to remove the varnish with a dremel or piece of sandpaper to ensure electrical connectivity. I removed the varnish on both chassis sides and the motor mount to ensure connectivity between the motor mount and the outer chassis side.



It could be a good thing to use a resistor to avoid a potential short circuit. As you ground the frame, a broken cable can cause a short circuit and in the end, a fire or broken electronics. I use a 2k-ohm resistor. I have however not done any deeper calculations of the resistor size, but think it will do. Unfortunately I do not have an updated picture of it. I will maybe add an updated picture later. These are old pictures from September 2008, which is even before my Scorpion 1600kv motor ;-)












·      Paranoid people can of course use the above-mentioned modification and the silicon spray at the same time.


·      Note that it could be the case that you do not have to modify everything according to this document. For example, maybe you do not have to ground the frame itself. We do not know… We did however not try one thing at the time (didn’t want to crash a few times to find the exact limit of what was needed). We did all at the same time. Now we are a few people using these modifications as stated above. A summary of all our flights is approximately 300-400 flights and no static electricity problem. SO IT WORKS!


·      You could use a CF boom instead of Alu. The same applies…. In either case you have to remove the paint/varnish and check the connectivity with a multi meter.


·      You can also use an opto isolated BEC to better resist spikes. You probably need a separate battery to take fully advantage of this. This is not in any way a guaranteed solution, but one of many small positive modifications (I don’t have it…)



·      Spektrum 2.4GHz receivers seem to be more sensitive to “brown outs” than others. By reading different forum threads is also seems Futaba 2.4GHz receivers are a little more tolerant. 35MHz also seems to be more tolerant than 2.4 GHz in general. NOTE: This statement is not mine, but a summary of all forum threads I have read regarding this matter!


·      There is also a new solution that according to the info should discharge static electricity into the air. It’s called “GFA7088 G-Force Static Wick For Trex 500” http://www.fast-lad.co.uk/store/gfa7088_g-force_static_wick_trex-p-3652.html I have not done any deeper investigation into this. This maybe works. It did not exist at the time we investigated and solved our anti static problems. If it works it is of course less work to implement….