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Model Forum / Radio Controlled / Air Models / May 2004Fried IPS
Hi All; I was out at the schoolyard some time ago flying the Rare Bear with an IPS DX-A setup and two Lipo cells. It was pretty blustery and overcast, and I was trying to get some altitude - I kept it full throttle all the way up, and it had to fight to get there. After that, I just shut down the throttle and let it come down in a nice, long glide. Near the ground, I went to apply some throttle again, and noticed the prop wasn't spinning! I managed to get a nice landing in, but the motor never turned under power again. I could turn it with the prop, but it was definitely stiffer. So, when I put the new motor in, I decided to check the temperature after some minutes of flying the other day. It was too hot to touch, although since then I've given this one a workout too, and it hasn't siezed yet. Is it normal for these little motors to get that hot? This is the stock setup, except for the battery pack (7.4 lipo versus 7.2 Ni-something). I did recently switch from a 750 E-Tec to a 730 Thunder Power. Great little plane, though! Dan. Dan, A few of us are just getting started on pylon racing with the Fan-Tastic AT-6 which was designed by the same guys as the Rare Bear. Mine also has the DX-A power unit and I'm flying it with a Etech 700 two cell pack. We are using the GWS 9x7 slow flyer props which provide decent speed and the power system seems to handle this well. What are you using for a prop? You may need to prop down some to decrease the load. Try reducing either the prop diameter or pitch somewhat. The Rare Bear should fly well on the 9 x 7. Keep in mind that GWS recommends a 150 mah 7.2 volt battery for this motor. Perhaps their logic is that the motor will get a chance to cool after every 150 mah of fuel consumption. I've gotten over 70 hours out of one of these $9.00 motors in another application (slow flyer). But I don't expect that kind of life in a warbird racer. The plane flies for at least 30 minutes on the Etech pack, but I stop every 7 or 8 minutes to let the motor cool. I bet you're right Mike - the plane's performance on the LiPo's is surprisingly greater than on the NiMH's (attributable to the .2 volts?), and I have flown for twenty solid minutes at a stretch some days. The day I seized the motor I was fighting the wind exceptionally hard, and trying to reach the cloud base - which I believe I did! I'm using the supplied three-blade, which, I believe is a 9x7, but maybe going to a two-blade would lighten the load on the motor. Pylon racing! I'll bet that's a blast, particulary with Bearcats and Texans! Is this indoor or out? Dan. > Dan, > [quoted text clipped - 14 lines] > racer. The plane flies for at least 30 minutes on the Etech pack, but I stop > every 7 or 8 minutes to let the motor cool. Dan, The performance increase was probably not due to the negligable increase in voltage, but rather the lipoly's ability to put out the amperage required by the motor. These things need cells that can reliably put out 2 amps over the complete discharge cycle to get full power. That takes a pretty big nimh pack (relative to this tiny airplane). We have been trying to settle on a non-lipoly cell (recent AMA terror alert scared off some club members) for the racing events and found that 160 mah nimh cells were no where near up to the job. Going up to eight of the 160 cells (9.6 volts nominal) still couldn't get performance anywhere near the performance of the 700 mah, 7.4 volt lipolies. Next experiments will be with (6) 150 mah nicads and (7) 300 mah nimh cells. Track down a GWS heatsink as another poster suggested. Limit full throttle runs with the 3 blade prop, or get the two blade prop. We are racing outdoors. It sure is a hoot to see a group of these things rounding a pylon! It is also fairly easy to convince others to make the meager investment to join in after they have seen the spectacle. > Dan, > [quoted text clipped - 14 lines] > racer. The plane flies for at least 30 minutes on the Etech pack, but I stop > every 7 or 8 minutes to let the motor cool. If you want to see some real performance out of that combo (IPS A) slip in 3s Kokam 340 and drop to a 7x6 prop. Same heat, almost twice as much out of the motor...Ideal for small warbirds and racers. I suspect one mistake was to just shut down after a hard work out. I would have run at low throttle for a few minutes to help cool the thing down. Keep thing circulating so to speak. Also, I do hope you have adequate cooling holes for the motor! Chuck > Hi All; > [quoted text clipped - 19 lines] > Great little plane, though! > Dan. I think you're right - had I let it idle, it may have cooled in the "moving" position - when I disassembled the motor (post-mortem, you know) the end-cap plastic around the bearing was melted and wallowed out, not to mention all the metallic flakes that appeared inside the can. That's a bit of a "design flaw" with this model - the spinner meets up almost exactly with the cowl and the fuse behind the firewall is pretty much airtight - there is NO AIR moving around inside this plane! I may have to put a scoop to the side of the cowl and cut an exit hole in the fuse somewhere... > I suspect one mistake was to just shut down after a hard work out. I would > have run at low throttle for a few minutes to help cool the thing down. [quoted text clipped - 26 lines] > > Great little plane, though! > > Dan. > Hi All; > [quoted text clipped - 16 lines] > setup, except for the battery pack (7.4 lipo versus 7.2 Ni-something). I > did recently switch from a 750 E-Tec to a 730 Thunder Power. yes, they do get up to near boiling point. Try a lttle oil on the bearings now and again. > Great little plane, though! > Dan. Does GWS make a heat sink for this class motor? if so, might want to add one, assuming that you have some decent airflow around the motor to carry the heat away from the sink!! The small GWS motors are very sensitive to heat so you must provide adequate cooling . A friend has one of the Fantastic Models AT-6's. Can't wait for him to get it together. Brian Allen |
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