Don/others, you have answered many of the sp400 questions I have had in some of your other posts. However I have many more. I am getting back into pylon (I am a retread quickie pilot), and I would like to try electric. I have designed an airframe (Don put a link my site that includes the plans) and I am more than familiar with the flying, but I am totally ignorant about the electric part. So here are my questions.

Do you suggest making your own battery packs, or buy them already soldered? What type of cells/packs should I start with, and what should a good pack cost to buy/build? What are zapped cells?
I have been offered an esc to start with. It has a built in BEC, and is rated a 30 or a 40. Is that a high enough level to handle a rocket motor on a good pack?
What kind of props are good to start with? and what keeps the prop sitting at 9 and 3 when not running to keep from breaking the prop or bending the motor shaft on landing?

I know I will think of more, but I bet that is plenty for now..

I'll quote the questions so I can answer out of order, and possibly in separate messages. I need to create a FAQ from this one because I'm going to give you detailed answers.

>> what keeps the prop sitting at 9 and 3 when not running to keep from breaking the prop or bending the motor shaft on landing? <<

Luck. There is disagreement over this one, but I'll tell you what works for me. The main runway at the field where I fly mostly is reasonably smooth grass. Normally cut pretty close. When your plane is gliding at no throttle, the prop will be windmilling. It sounds bad but actually isn't. My first ESC had a brake on it. When you pull the throttle to idle, the shaft is stopped for 2 seconds. I was breaking a prop about every third flight, because the prop would sometimes be sticking down stopped. It's like a stake sticking down, and the plane would cartwheel. I had noticed that when I came in with it windmilling, as long as I kept the wings parallel to the ground there was no problem. Then one day as I was coming in, a little long actually, I saw the prop sticking down. Balls to the wall and missed approach without incident even though the battery was beginning to weaken. As I was going around, it hit me. Normally I glide all the way from a point downwind, through the base, and then final. On the missed landing, I thought I was a little short and added a little power. So the brake was engaged and the prop was not windmilling. Several times with a windmilling prop, I had noticed that just as the belly got right at the grass, the prop just kind of bounced off the grass and there was no problem. The biggest thing with a broken prop on landing is a broken plane. The Graupner and APC props are tuff enough that having one grab the ground will cause the plane to cartwheel, turn around, etc. I often found the broken off prop blade at the touchdown point, not near the final resting spot.

I finally had to retire a Graupner CAM prop after 15 or so flights because it was starting to deform a little. I'll take 15 over 3, 2, or 1 flight for $5 any day.

Asphalt works about the same way. If your grass is taller than the clearance from the bottom of the planes belly to bottom of the wing, you are more than like not have a good landing because one tip or the other is going to catch the grass and a cartwheel/turn around is almost guaranteed. So it is better to seek out tall dense grass. Wheat in the soft stage works ok, too.

Recently someone figured out that the FF guys have a solution to this. It could lead to a nice development, and make the answer much simpler.

>> Do you suggest making your own battery packs, or buy them already soldered? <<

Buy them pre-made. They don't cost much more than making them yourself. If you defray the shipping cost over 2 or more packs, you can't make them much cheaper than you can buy them.

Try Mr. Nicad at Batteries America. Make sure you tell them it is a motor power pack so they put the right leads on it. They will also put the connector of you choice on for not a lot more than the cost of the connector. They also make them in a variety of configurations. See their ads in the mags and the web site.

Soldered connections are better if they are done properly. But it is very easy to damage a NiCad cell unless you really read up on it. Save yourself the hassle.

>> What type of cells/packs should I start with, and what should a good pack cost to buy/build? <<

It depends on the size of the plane. If it is a 16 oz or lighter Speed 400 powered plane, you will probably be limited to 500AR or 600AE packs by weight and physical size. The AR's are higher discharge rate and the AE's last longer because they don't have as high a discharge rate. BTW, the A refers to the diamter of the battery cell, as in AAA, AA, etc. One confusing one for me every time I see it is SCR. As an EE, I think electrical component, but what it actually means is Sub-C high discharge Rate. Sub-C's are a little smaller in diameter than C cells.

Read this article and then visit The R/C Battery Clinic .

>> What are zapped cells? <<

Applying a very high current to a cell for a very short period of time allows the cell to discharge at a higher rate. I believe it is because the resistance of the cell is lowered slightly.

It is only worthwhile for cells with a certainly amount of mass which is usually related to the storage capacity.


I'll add one of my own

>> Can I use NiMH batteries in a Speed 400 pylon plane? <<

Not if your primary goal is speed. Endurance, yes. Speed, no. NiMH's don't handle high discharge rates well. They get too hot and are permanently damaged. When I first started flying Speed 400, I bought 3 packs: 7 cell 600AE, 7 cell 500AR, and a 8 cell 550 NiMH. I tried the 600AE. It stayed reasonably cool and lasted about 5 minutes. The 500AR lasted about 3-4 minutes and was faster, but was pretty hot. I started to try the 550 NiMH, and I was ready for the hot rod output of an extra cell, but the power output was audibly much lower, so it never got flown in the pylon plane. It gets used in a park flyer instead.

>> I have been offered an esc to start with. It has a built in BEC, and is rated a 30 or a 40. Is that a high enough level to handle a rocket motor on a good pack? <<

If it doesn't weigh much more than an ounce, it may be useable. 30-40 amps is more than any Speed 400 can handle. You can run two 6V Graupner Speed 400's off of an ESC in that range. The impedance and switching rate of the speed control determines how it will perform.

Read the Speed Control section (at the minimum) of this FAQ.

Don't start out with the Rocket motors. They are less tolerant of break-in method and you're lucky to get 10 good flights out of one. Start out with the 6 Volt Graupner Speed 400 motors. You usually get at least 30-40 flights on one, and they aren't as easy to hurt.

BTW, don't hook up a 7 cell pack to a motor with no propeller on it. Also keep in mind that these things produce as much power as a 1/2A nitro engine. And also be very careful about not having them restrained properly when you apply power. Unlike a 2 cycle engine, it only takes a bump of the throttle control on the transmitter to go from silent to eating up stuff like fingers.

>> What kind of props are good to start with? <<

It depends on the motor. On a 6V Graupner Speed 400, a Graupner CAM 5 x 5 works well. You can also use the 5.5 x 4.5, but you will probably not go as fast. This depends on the airframe though. If it is a draggy airframe, the 5.5 x 4.5 may actually work better. You can also use the APC 5 x 5.

If you are using a Rocket 4.8V motor, using anything bigger than a 4.7 x 4.7 will burn the motor up, possibly/probably in one flight. The APC seems to be preferred over the Graupner CAM for this motor.

And once again, I'll add one of my own

>> How do I ever figure out what prop, motor and batteries to use?

There is a program called MotoCalc that has a large library of characteristics for props, motors, and batteries. It let's you play with "what if" scenarios. It is extremely useful for determining how far you can push that motor or ESC.

Don, thanks for the info. I know now that I will get going in the right direction.... A couple more questions if you don't mind.

I am guessing because there is an ESC, that no on-off switch is necessary for the radio and that plugging the motor battery would effectively be the switch. Is this correct?

What is a good entry level battery charger to begin with? I am working with a severly limited budget, but I imagine the charge the batteries recieve would have significant effects on motor runs, and in the end the speed of the racer...

In looking at many of the current sp400 racers on the market, I see no vents for cooling the battpack. Are they not necessary because of the short motor runs, or are people just under the impression they would just cause too much drag?

All of the current designs I have looked at have 2 ailerons. All of our old half-a pylon designs tended to have 1. Any thoughts on a single aileron sp400 racer?

Thanks again for the great answers.

How about looking at our newest racer,The T-strike.
It could be the plane you are looking for.


Greetings,

Jan
S&D Modells
http://www.valkenswaard.myweb.nl