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Good suggestion Hank.Here we go guys, any and all E-36 topics. I will begin building next years model in a couple of weeks. I will post the progress. I encourage any and everyone else to do the same. If you already have a model built, post it. If you cannot post an image, describe it. Hopefully it will inspire others to build. I think that the efforts of Vic Nippert and the others that put this provisional class and it’s rules together should be applauded. I think the best way to show our appreciation is by participating.
I have ordered a motor/gearset from Balsa Plus and expect to build a Sparky for it. I will report the motor performance when it arrives.
I am wondering just how much current these tiny 1/3AAA cells can deliver. I tested a BP 4.8 volt motor on a GWS gear set on a 8×4.3 prop and got 8000 RPM on a battery pack made with 1/3AA cells. When I tried the 1/3 AAA cells, the RPM was under 4000. I was pulling about 1.6 amps. I have a MG 1 about assembled for testing.
What is the gear ratio on the gearbox? I tested a GWS 4.8v “A” motor (2.8:1) with an 8 X 4 prop using Sanyo N150-N cells resulting in a 4amp current delivering 16watts. I cannot measure RPM. So far it is my opinion that this is the best off the shelf combination for E-36.
I also tested the MM-1 in the GWS 300 size gearboxes and N150-N cells with the following results:
2.8:1 / 8X6 delivered 21w drawing 6a
6:1 / 10 X 8 delivered 10w at 2.1a
6:1 / 11 X 8 delivered 11w at 2.5a
6:1 / FIG blades delivered 19w drawing 6aIn every instance where the current was above 4a the performance tapers off way too fast. The MM-1 geared with the GWS out weights the the GWS “A” motor 3:1. I am sure that there are lighter options for gearing the MM-1, Penn-Vally has one. Gearing the MM-1 may still offer the best performance, but I have yet to find the optimum gear /prop combination. The play, I mean work continues 😀 continues………………………………………
Jim,
How are you gettting the watt numbers? Using a watt meter? Reason I ask it your data shows two 6 amp draws at different watt numbers. This woulds say the voltage is dropping on the lower watt reading.I have yet to see any currrnts that high. I may make up a pack using larger cells so I do not exhaust the battery so fast during testing.
Wow, an 11 inch prop.
What is the only important number is thrust. And that is the hard one to measure.
BMJR sent me an MG 1 which is (I think) a MM 1 with a 4.8:1 gearing. I will get some data on it today.
I sure wish this stuff had some markings. I hate having to count gear teeth. And the motors all look the same. I can tell a difference in resistance, but that is all.
Where did you find the Sanyo cells?
Hank
I am using a Astro Whatt Meter Model 101. It measures voltage, watts, amp draw and cell cap. I bought the Sanyo cells at Muncie Hobby. Balsa Products has a instrument to measure thrust that transfers the force from the motor to a digital scale. It looks pretty neat. http://www.bphobbies.com/view.asp?id=A0320107&pid=V786359
I am holding the motor in my hand to gauge thrust (you might be a redneck if…….. 😆 ) Can you use RPM, prop dia. & pitch to calculate thrust? What are you using to determine the RPM?
Each time I test I top off the batteries and take readings every 5 sec. You are correct the voltage drop with big gears and big props is huge. It has to have a negitive effect on the cells. I like smaller dia. props at higher RPM’s. It keeps the weight closer to the CG. I hope to start building tomorrow.I tried to get some data on my MG1 today, but I have no faith in the battery pack. At only 1.5 A draw, the voltage sucks way down. And that is fresh ovv the charger.
And, I found something that disturbs me. I have a pretty costly digital meter and the motor RPM is noticeably lower when my meter is in the circuit to measure current. With out the meter I am truning the supplied prop ( 7×8?) at 3000. With the meter in it shows 1.5 A and RPM of 2400. This is not good data.
I have a digital optical tach that I have used for many years. Have to do test outside as it needs sunlight. Or a flashlight inside.
I do not know how to convert RPM and prop data to thrust as prop blade shape as a big effect.
Why don’t you buy one of those thruist devices and do testing for all of us? 😉
Jim, I looked at the thurst unit and it seems very simple. You could make one in an hour. I expect most of us have a postal scale or similar that would work fine. You just tare out the torque due to the weight of the motor before taking a measurement. If you make both arms of the lever the same length, there is no math to do. I do not see what you are expected to do with the battery and stuff. I think I would make the platform larger to hold it as well as the motor.
You might want to put a heavy base on it or the unit could topple over.
My watt meter has an option to use power from a second source when measureing lower voltages as we are. It is very accurate. It sounds like you may have bad cells. I went to the NAT’s last year with bad cells and did not discover they were bad untill I got the Sanyo cells at Muncie Hobby on the way home.
The thrust meter does look easy to build. My scales are triple beam balance scales. Perhaps Santa will deliver one. Untill then I will continue the redneck approach.I have a real wattmeter too,with the external power provision, but the connectors on it are all Deans Ultra for high current, so until I make some adaptors, I was using the current measuring feature with my digital multimeter. In theory, the way it measures current is no different than that used in the wattmeter. You measure voltage drop accross a very tiny known resistance value.
I am going to order some Sanyo N cells.
Wow, I thought everyone had a digital scale. They are so inexpensive and so quick and easy to use. I have a single beam balance scale that is only used when I need accuracy down to the grain level. (use to load red neck ammunition)
For most needs, I use a red neck scale. I pick up a piece of wood and say “this feels good” or “this is too hard”.
I realize this is supposed to be E-36 but I have been in contact with Ron St. Jean and some of the information is applicable to E-36.
If you go to the link below you will be able to read some of Ron’s experiences with converting his Ramrods to electric power.
As soon as I get the time I will also be posting a link to his thoughts regarding the E-36 rules and its effect on the promotion of free flight.
I’m a two fingered hunt and peck typist so it takes time
http://www.newg.info/stjean_f1q.html
Bob Sisson
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