I just got back from flying the Super Cub with its newly outfitted Speed 480 BB Race motor and for the first 4 minutes it was amazing. The plane flew through the air with authority and power. I could just let it climb at about a 50 degree angle and it just kept going up and up and up without losing speed. Doing big loops was no problem at all. But, within a few minutes of takeoff, the motor began sputtering and glitching, so I thought I’d give it a rest and cut the throttle and glide a bit, but when I cut the throttle, nothing happened. The motor kept purring away full tilt. I still had control of the plane, but I couldn’t stop the motor. Then 5 seconds later the motor dies, completely. I was about a hundred feet up and a 50 yards away or so, so I glided back for a gentle landing. Upon inspecting the plane I immediately noticed the smell of burned IC’s. That really gross, stays-in-your-nose for hours kind of burnt electronics smell. The motor didn’t respond to any throttle inputs, but the rudder and elevator controls were still in tact, obviously since I successfully landed the plane, but it looked as though I had smoked the ESC.
The motor felt warm, but not unlike the stock motor. It was within tolerable limits for a few minutes of full running. The batteries were also warm, but not hot. Those darn Tamya plugs didn’t melt though, too bad, but they were also warm. However what was hot was the receiver/ESC unit. I dragged the plane inside and pulled out the receiver unit, now just a bit warm, and that burnt silicon smell was strong. Upon inspection of the circuit board I noticed quite a few things gone wrong. I’ll let the pictures tell the story, but the one FET that basically is heart of the ESC, was completely cooked. It must have already been in close proximity to the jumper for the voltage cutoff because it melted right into that little jumper. The FET looked black and burned on the one side and the PCB looked charred around the 3 leads. It wasn’t until I turned it over that I realized how hot it must have got, it actually re-flowed the solder on the IC leads! One of the leads isn’t even connected to the trace on the board anymore, it’s just a lead in a hole with a big blob of solder further down the exposed trace. Instead of nice shiny solder joints, there were cold solder joints on the other leads, and the rest of the solder around the area looked cold too. Assuming the solder Hobbyzone uses is a standard 63/37, tin/lead alloy solder, the chip must have reached 183ºC (or 364ºF) to melt the solder around the leads of the part like it appears to have done. Now that’s pretty hot. As it turns out though, these power FETs are designed to operate up to 175ºC, so that’s all it took to melt the solder on the board.
I’m going to try and just replace the one FET, maybe stack two of them on there, or get one that can take the extra current, since it should only be a couple of bucks to fix. I think the rest of the receiver is still working fine, since it it still responds to controls from the radio. Download the data sheet for this power FET here. That exact same part should get my cub flying again but I’d have to I re-install the stock motor, which I might do. But they make FETs that can handle a lot more current also, so I may look into that as well. I’d like to try out the 480 motor a bit more.
In the end, even after less than 5 minutes of run time, I think the Graupner Speed 480 BB Race motor is one possible upgrade to the stock motor, however, the stock electronics need to be replaced with an aftermarket radio and at least a 35A brushed ESC. I still had a little bit of interference but a new radio would most likely clean that up. Other things I didn’t get to try was cutting a 1/2″ off either side of the prop, thus making it a 9×8 instead of a 10×8, possibly allowing a few more RPMs to squeak out and maybe a bit more thrust. Also, I think an 11T pinion would fit and still mesh with the 36T spur gear. That would provide a gear reduction of 3.27:1 instead of 3:1. This would reduce some of the stress on the motor, reducing the current draw, and lighten the load on the ESC and batteries. And lastly, I didn’t get to try out a 3S lipo, which ultimately would be the final piece of the Speed conversion for achieving ultimate flight performance. But alas, this will all have to come another day. Until then, check out these pics of one fried speed controller.
Hello Dan, I have enjoyed your blog. Just a quick question. The brush 480 upgraded is that made by Graupner and did it fit into the factory motor mount. Can you list your cub upgrades for me. I am currently working on ailerons and flaps just for fun of course. \
Patrick
Hello, I see that that motor is 7.2 volts, are you running more that a 7 cell pack? Will a 9-8 cell pack be compatible with this motor.
Yes, the 480 fits into the stock motor mount, but it doesn’t go in as far, there’s about a 0.150″ gap between the back of the plastic part where the motor is suppose to sit up against. You could put some spacers in there, I just didn’t tighten down the screws too tight. I used some longer 2.5x10mm screws to hold it in.
The voltage rating means very little with respect to maximum allowable voltage. I was running an 8-cell pack, but this motor can run with a 3S li-po pack.
I haven’t done any other upgrades other than those I’ve written about here. Just today I flew my SC for the first time with the new Poly-Quest 3S lipo and wow, it was amazing! Hands down, the best upgrade one can do. I totally want to add ailerons too, let me know how you do it when it’s done.