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In Calliope we tried the NTM 28-36 750 KV. Once they go, they go like stink. Unfortunatly, getting them to go is a bitch.
I'm redoing the drive with NTM42-35 750 KV in a desperate attempt to save the idea. Weight will be my enemy in this.
An external sensor kit combined with a good sensored speedo could save the 28-36 setup. After all, those motors are in the same power-range as the common batterydrill setups.
And I have a backup plan. But that ain't for next week.
I've looked at pretty much copying the methods use by Charles for the external sensors, the problem is that you still have to tune the sensor to the motor, and this will change every time you pull the assembly apart. My currently idea is to try to develop a PCB that will fit inside the motor near the mount and stator to position the hall sensors between the stator teeth. This will remove the need to tune them in and will still provide enough cooling to avoid heat damage (A few industrial brushless motors I have seen have the hall sensors epoxied between the stator teeth)
http://alienpowersystem.com/product-...shless-motors/
I forget if this has already been posted, but still. Sensored outrunners.
They look interesting but a bit oversized for featherweights. The 42mm outrunner is about the best fit but its low KV and 22V limit makes it a bit low revving for my taste. The high voltage car ESCs also look interesting, they are the first I have seen that work up to 44 volts.
I wonder if Alien Power would consider a custom sensored outrunner for the bot community? A 35mm motor with a KV of about 1000 and a 22V working voltage would work really well with a Banebots P60 26:1 gearbox.
They seem open to custom spec motors so it is probably worth an ask.
I've seen the APS range but price and variety was the stickler for me.
I can get the NTM motors in a range of KV's and voltages from the AU warehouse for $30-45 shipped. This is pretty important if we decide to sell these as a product and it also allows people to buy replacement motors quickly from their own local hobbyking warehouse (UK, EU, AU, US).
If someone is keen to use the APS units for their own brushless drive tests, I'm keen to see the performance :)
Just trying to settle this in my own head...
There seems to be two schools of thought:
1: Go for a sensored inrunner setup with a higher KV and more reductions, the advantages being it is easier for the motor to start because of the gearing and because the ESC knows were it is.
2: Go for a large stator sensorless outrunner with a lower KV and less reductions where you rely on the greater torque of the motor to get the machine moving despite the ESC not necessarily being able to remain perfectly synchronised.
The first option seems to be having more success but needs a high reduction gearbox to make it work which is expensive (Just thinking banebots or a custom setup here). The second is easier to do as it requires less reductions but may not work at all of you get it wrong.
Is that right?
I am going to see if I can scrounge 10 minutes with one of the motor engineers at work and see if they know anything that might be able to help. Perhaps there is a way of making a sensored outrunner behave itself on start up.
What about a low KV sensored outrunner like the Alien Power motors?
I'd have thought that it gives you the best of both worlds. There's the price to consider, and I'm not sure what people's opinions are on their ESCs but then you've got your startup torque and something that's low speed enough to have a single-stage gearbox, like Speed 900s are at the minute.
Unless of course I'm missing something with it all, I've never actually used a brushless motor so I'm not 100% what they're like in practice.
I wonder if you could have a sensorless with a gearbox with a lot of slack built into the system- this would slightly reduce handling but it would give the motor a chance to get going before its put under load. Perhaps a simple clutch even!
Yeah I think backlash plays a big role in trying to use sensorless systems. Doubt it'd be at all noticeable with 1/4 turn at the wheel before anything engages, which could be several full rotations at the motor end.