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Take a look at this modified Amazoom. The fuselage on the original model was destroyed. The new fuselage was built as a profile over the plans with a carbon tube as it’s backbone. The motor is a GWS LPS 4.8v 4:1 with a 8 X 4 folder. The motor timer is a mosfet type, the DT is a viscous. The batteries are SR 190’s. It has been flown 3 times in high winds with promising results. I am building 2 other prototype models. More to come.
What is the RTF weight, Jim? Have you thought of just using a carbon boom fuselage? Is that some sort of heat sink I see on the mortor? Nice looking.
Thanks for the kind comments guys. Hank, that is a heat sink, good observation. The motor does not realy need the heat sink, but I missed the CG when I placed the battery and the heat sink brought it back. The model also needed the additional weight. The model is 5g light right now. This model was put together primarily to get an idea of how the LPS motor would climb a 150g model. The cord on the Amazoom is a little narrow for 150g min. weight. The model that I am currently working on does have a carbon tube fuselage. Ed, I agree, this is already a lot of fun!
😆 Not quite. I am still torn on the power package. If we did not have the min. weight it would be easy. I am working on getting the geared MM1 lighter.
Jim, I just noticed that you said LPS motor. Did you mean IPS? The GWS part naming system is terrible, IMHO. I have spent hours on their web site and still do not understand it.
Yes, LPS motor. I agree about the confusion. I have purchased and tested both and have determined that there are three basic differences.
1) LPS (Light Power System) is eight grams lighter than the IPS (Indoor Power System). The weight difference is due to the larger dia. prop shaft on the IPS (3mm). Both still accept the same props. The prop is centered on the nut, not the shaft.
2) The LPS is designed to mount on a round tube. The IPS is designed to mount on a rectangular stick.
3) On the IPS the actual motor is press fitted into the gearbox. On the LPS it has two mounting screws. This is not of importance to us now, but in the future, if brushless motors can be used it will be important. FYI Feigao has a brushless motor that will mount in the IPS that cost $22.There are several aftermarket GWS clones if you do not like plastic.
The most important thing to remember is the motor. Untill very recently the IPS was not offered with a 4.8v motor. The IPS is only offered with a 4.8v motor in one gear ratio( 4.1:1 ). You can purchase the gearbox and motor separately if you want a different gear ratio.
The LPS is offered with a 4.8v motor in three different gear ratios. LPS or IPS, if you are not useing a 4.8v motor in E-36 the performance will be less than it could be. The real confusion is in identifing the difference between a 4.8v can and a 7.2v can. I have been told by a GWS rep that the markings on the can have nothing to do with the voltage rating. I believe him. Every 4.8v that I have has different markings on it. I mark them with a sharpie. I hope this helps.
Jim, thank you for a finally understandable picture and explanation of the two gear sets. I have been takikng to Taiwan and it seems we can obtain added gear sets if we order them. I have heard already of bent prop shafts so I wonder about using the LPS even with the 8 gram weight savings. What is your experience?
It would seem that props up to 10 inches with a higher gear ratio may give higher thrust on 4.8 volts.
I believe we should be able to measure the resistance of the motor windings and see a marked difference between the 4.8 and 7.2 volt motors.
Of some interest is that GWS says the RLC motor is really 2.4 volts and we are just running them harder.
There is also a RXC motor that is not acceptable for our need.
How can the LPS be lower weight than the IPS? My IPS is 8.6 grams without the motor and the motor is 17.8 grams including a pinion gear and wires with connector. If the LPS is 8 grams less, it is made of negative gravity. 🙂
The LPS is lighter because it has less steel in the prop shaft. Which gets us back to your question about strenth. I too have bent the prop shafts on LPS gearboxes. It is not difficult to change the prop shaft, and they are not expensive, but who wants to do that at a contest? I have not bent a shaft on a trimmed model. It’s the trimming that is risky. It gets down to risk management and weight.
I agree about measuring resistance. I knew that the RXC motor was rated for a higher voltage, but I did not know that the RLC was rated at 2.4v. Makes me wonder about the necessity of the heat sink. Back to risk management and weight.
I do not have a means of measuring static thrust much less dynamic thrust. I wish that I did. I have seen the static thrust set up offered by Balsa Products. I have been trusting the data thats already out there.
I canot explain the negative gravity. I weighted both motors to verfy the weights and they were within 1g of the posted weights. When I get time I will take them both apart and weigh the componets.Jim, I can understand how the smaller diameter prop shaft would reduce the weight, but it is not possible for that the account for 8 grams. If it did the LPS gear box would weigh under 1 gram.
I see no need for a heat sink with a 25 second run. Unless we start pulling some serious current.
Do you have a good ohmmeter so we could do some measurement comparisons of the motors?
What about getting a threading die and putting the prop closer to the housing to reduce bending?
What folder are you using? I recall I found a nice low cost one on the internet and mentioned it to you, but I do not recall where it was. Have you tried to make your own folder from a GWS EP?
Hank, there must be a difference in the motors. I used the weights GWS gave for the motors and weighed them myself. The only instrument I have is The Astro Flight Watt meter (Amp/W/V).
Threading the prop shaft closer to the gearbox sounds like a good idea. The rubber nose cone helps. I like to leave them long with a folder mounted close to the end. It helps get the weight of the motor closer to the CG. The folder that you mentioned is in a previous thread. I am certian that you posted a link. I like to use CAM blades from Hobby Lobby on a home made H-hub. I also have a few blades that came with Potensky outrunners that I like. I will attach an image that illustrates a coupe of mounting and blade options.
Jim, I did some resistance measurements and the 7.2 volt RLX motor we do not want (yet looks identical to the 4.8 volt RLC motor) is quite a bit higher than the 4.8 volt RLC. I am seeing 0.8 to 0.9 ohms on the 7.2 motor and 0.1 to 0.2 ohms on the the 4.8 volt RLC. I will be the first to admit that it takes a top of the line meter to make this measurement. The $30 ones will not measure that low with any degree of accuracy.
I note that the LPS has the smaller (and more prone to bend) prop shaft compared to the 3 mm shaft on the IPS. But, there is another significant difference, the IPS is ball bearing and the LPS is not. At least that is how I read the GWS data.
GWS does offer a little plastic prop saver where an o-ring gives when the prop is hit. This adds only a small weight and may be useful in saving prop shafts except in a real nose down hit.
Finally, GWS has a stainless steel prop shaft adapter that fits directly on the RLC motor and held with two set screws. This is of course for direct dirve that may be interesting to look at. But I think the hole in the adapter can be enlarged a bit to fit on the IPS or LPS gear units. One would, of course, cut off the original shaft when using the SS adapter. I would expect the SS shaft to be very hard.
Gear ratios all the way up to 11:1 are available for the LPS. According to the GWS data, thrust really goes up when used with a 10 inch prop.
GWS has suggested a way to make a folder from their standard EP prop. I have requested a drawing from them as I am not clear how this is done. I am a EE and weak in mechanical stuff.
Hank, I had a couple of ideas I tried to make a folder from the GWS Prop. I tried them on a EP1047 prop. One was to cut the blade near the hub and glue a small cut down version of a Du Bro hinge the rc guys use for elevator hinges on the back of the prop. I used CA for the glue. The other version I used was to cut the prop near the hob and attach a small piece of .062 dia aluminum tubing side of the prop with 5 minute epoxy, I put a .021 dia music wire thru the hub bent it on both sides of the tubing and attached it to the prop by binding thread around the prop and the wire and adding a drop of CA to the thread. The prop weighed 7.6 grams before modifications and 7.8 grams after, so not much weight gain. I will try to attach a couple of pictures showing the DuBro hinge on one blade on the wire hinge on the other. One of the problems might be the reliability of the glue joints. I like the tube and wire hinge the best, also a small patch of silk around the tube would be a good idea.
Ed
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