Originally Posted by stumax

Is yours an 8mm or 5mm version? You get very little tweakability with the 8mm versions, and I've found with the 8mm motors that unless everything is 100% perfect they have a "hard" feel to them compared to a 5mm version at the same level of balance (or imbalance to be more precise, as everything has a tolerance to it). I've also found that even though my rotors are dynamically balanced to within 0.1gmm, sometimes when you put them on a motor it just doesn't feel right, perhaps the slight imbalance of the rotor and motor are aligned out of sheer bad luck and work together to double the imbalance. Have you tried removing the rotor, rotating it 180deg and putting it back on? What motor are you using? I've recently been trying (for 3 weeks now) to get a 110-47 with Neu 1527-1.5Y to run smooth enough, I even took the rotor to a friend's turbocharger shop and we balanced it on his $30K Schenke dynamic balancer to about 0.02gmm, which is about as good as you can get without spending a week doing it. It made no difference, this rotor/motor combo just won't run smooth, I need to change the design a little to change that system's natural frequency. Put that rotor on a HET 700-98 series motor and it's like a turbine, you could balance a coin on edge on the shroud, it seems the Neu 1527 has so much cogging torque (I can see this massive cogging torque with an accelerometer stuck on the shroud whilst running it) that even though it's balanced it just doesn't feel as smooth as it should. I think the cogging torque, the frequency of which is a whole number multiple of the rpm, is exciting a resonance mode in phase with the rpm.

What you can do is loosen the M3 capscrew holding the spinner in place, just a little bit, then push the spinner over to the side where your tape is. It's a bit hit and miss, but the final tweaking sometimes is. Note that you can't take the spinner off, that screw is what holds it all together, but you can get a bit of adjustment by doing that. Alternatively, you can add a small spot of something like JB Weld (alum or steel filled epoxy) inside the rear of the rotor hub. If you can weigh the piece of tape accurately enough you can calculate how much mass of epoxy to add, it will be in the ratio of the distance of the centroid of the piece of tape to the axis in proportion to the radius of the rear of the rotor hub. As a guess, I'd say the centre of the piece of tape may be twice as far from the axis as the radius of the hub, so that means you add twice as much mass inside the hub, ie mass1 x distance 1 = mass2 x distance2. This will only be approximate as the tape won't be in the same plane as the inside rear of the hub, but it should be close enough.

The new 80mm and 89mm rotors have been very much redesigned recently, and are now 25% lighter than before (which means with the 5mm shaft the whole unit is about 1oz lighter), and the rotor's CG has moved closer to the motor, reducing the overhanging mass considerably. This now means that we don't need 8mm shafts, a 5mm shaft works just fine, no more resonance issues, and you have the tweakability it offers. I still do plug and play SM89-45 units with 8mm shafts for now as I set them up and tweak them to be perfect, but non plug and play units and all SM80-45's will come with the new style rotors.

Stu.

Hi Stu, thanks for your expansive reply! It's a HET 700-68 1125 motor with a 5mm shaft. I will try rotating the rotor on the shaft and also the spinner trick.

Originally Posted by pavcon

Does that mean they will also pull less amps???

Nope, nothing else has changed, although I have found that a fan which vibrates does absorb power.

Stu.

Originally Posted by Kwahn

Hi Stu, thanks for your expansive reply! It's a HET 700-68 1125 motor with a 5mm shaft. I will try rotating the rotor on the shaft and also the spinner trick.

With the 5mm shaft, make sure the rotor is pushed as far back as possible to reduce the overhung mass. I'm surprised the rotor is a tight fit on a HET motor, their shafts are usually 10um smaller in dia than Neu's, which makes them easier to tweak. I find they nearly always run dead smooth at full throttle, but at about 800W or so they sometimes hit a resonance mode which can be tricky to iron out, I can usually do it on one battery.

Stu.

Stu can you do some 6s and 8s setups too?
the 1400kv het motor also comes in 8mm shaft now
have you got any numbers for those setups??

Originally Posted by stumax

Nope, nothing else has changed, although I have found that a fan which vibrates does absorb power.

Stu.

I was reffering to the lighter rotor.. if because it's lighter it will draw less amps.. or =does this makes the rotor spin faster so the difference is covered ?
don't know just assuming here.

Originally Posted by stumax

With the 5mm shaft, make sure the rotor is pushed as far back as possible to reduce the overhung mass. I'm surprised the rotor is a tight fit on a HET motor, their shafts are usually 10um smaller in dia than Neu's, which makes them easier to tweak. I find they nearly always run dead smooth at full throttle, but at about 800W or so they sometimes hit a resonance mode which can be tricky to iron out, I can usually do it on one battery.

Stu.

Today I went back to messing with the fan. Nothing changed after rotating the rotor on the motor shaft, and loosening the spinner and pushing it toward the lightest blade didn't do anything for me, nothing my hearing or my phone with vibration meter app could pick up anyway. Without tape, an audible and measurable vibration was present. After some fidgeting with the spinner I noticed that it could be turned and thus would enable balancing by giving it a small imbalance to compensate for that of the rotor. I removed the spinner, drilled a little hole and put it back in. Marked the spinner and made test runs with it lined up with all the blades one by one. It turned out that I had removed too much material so I drilled a counter-counter-balance hole of maybe half the size opposite the first one. Some more test runs and adjustments and voilą, smooth as silk! Just whoosh!

Originally Posted by pavcon

Stu can you do some 6s and 8s setups too?
the 1400kv het motor also comes in 8mm shaft now
have you got any numbers for those setups??

Do you mean with 8mm shafts? Why? A 6S setup is likely to be 2500W max, no reason to use an 8mm shaft then. With the new lightweight rotor there's no reason to use an 8mm shaft unless you're really pushing it, ie >4kW.

The 1125kV motor on 8S gives about 2.4kW, depending on cells, that's a pretty good option for most medium power setups.

Stu.

Originally Posted by pavcon

I was reffering to the lighter rotor.. if because it's lighter it will draw less amps.. or =does this makes the rotor spin faster so the difference is covered ?
don't know just assuming here.

No reason for less mass to translate into less current, all else being equal. Mass affects acceleration only, so a heavier rotor will draw more current for a fraction of a second as it's rpm increases, but once at full rpm it will behave the same as for a lighter rotor.

Stu.

Originally Posted by Kwahn

Today I went back to messing with the fan. Nothing changed after rotating the rotor on the motor shaft, and loosening the spinner and pushing it toward the lightest blade didn't do anything for me, nothing my hearing or my phone with vibration meter app could pick up anyway. Without tape, an audible and measurable vibration was present. After some fidgeting with the spinner I noticed that it could be turned and thus would enable balancing by giving it a small imbalance to compensate for that of the rotor. I removed the spinner, drilled a little hole and put it back in. Marked the spinner and made test runs with it lined up with all the blades one by one. It turned out that I had removed too much material so I drilled a counter-counter-balance hole of maybe half the size opposite the first one. Some more test runs and adjustments and voilą, smooth as silk! Just whoosh!

Good stuff! I'm still puzzled as to why it was vibrating, as it was balanced here to a very high spec. I'm wondering if the motor itself has an imbalance, or if the shaft has a slight bend. Good to know it's running well now, though.

Stu.

I have the 1125kv built by Stu in-stock

Originally Posted by stumax

Do you mean with 8mm shafts? Why? A 6S setup is likely to be 2500W max, no reason to use an 8mm shaft then. With the new lightweight rotor there's no reason to use an 8mm shaft unless you're really pushing it, ie >4kW.

The 1125kV motor on 8S gives about 2.4kW, depending on cells, that's a pretty good option for most medium power setups.

Stu.

Originally Posted by BILLYDSRC

I have the 1125kv built by Stu in-stock

and here I thought you were selling the CS copy?

LOL... Come on Mike we all know that the CS are a peace of CRAP

Originally Posted by Mike Warren

and here I thought you were selling the CS copy?

LOL Mike

Originally Posted by stumax

Good stuff! I'm still puzzled as to why it was vibrating, as it was balanced here to a very high spec. I'm wondering if the motor itself has an imbalance, or if the shaft has a slight bend. Good to know it's running well now, though.

Stu.

Isn't it also a matter of how the fan was mounted during your in house balancing? I mean if it sat just a little out of center on the shaft there then it would only run well with a different motor if one happened to replicate the same angle. Anyway, which exhaust diameter is good for the sm89?

Nicolas

Originally Posted by Kwahn

Isn't it also a matter of how the fan was mounted during your in house balancing? I mean if it sat just a little out of center on the shaft there then it would only run well with a different motor if one happened to replicate the same angle. Anyway, which exhaust diameter is good for the sm89?

Nicolas

For my balancing I have a piece of hardened ground steel shafting 100mm long which is dead straight (10microns/m straightness) and the rotor is a light press fit over it, I heat the shaft adapter up and let it shrink on, when it cools it's pretty tight. That way there are no grubscrews to tighten and possibly put it off centre. The front of the rotor is machined in a similar fashion, pressed onto a short stub shaft held in a collet chuck in the lathe, then the front of the rotor blades and front clamping ring are machined to located the spinner locating ring so it's all concentric within 0.01mm.

The exhaust dia depends on what model you have and what the inlets are like. I'd start with 74mm and if you want a bit more speed you can close it down. Smallest I'd go would be 68mm for a small, light, clean model wanting high speed. Not sure what size Billy D is using for his Viperjets, Billy?

Stu.