Hyperion Z3025 Shaft Length

[DKNguyen]

How long is the shaft on the Z3025? ie. is it long enough so that a pinion can slide onto it and leave some shaft sticking out on the opposite side (while still having the pinion far out enough to to mate with the transmission gears)? The reason is for use on the RC4WD aluminum CLod gearbox. I wanted to place an absolute magnetic encoder through the gearbox hole normally covered by the dust cover on the opposite side of the motor and couple the two shafts together with a shaft coupler to get sensored commutation for the brushless motor. I don't think sensorless is so good at low speeds especially where there are lots of stop/starts and starting up under high torque.

Otherwise I would have to use a pinion on the encoder shaft and mate it to the motor pinion which is more prone to wearing and slip my poor meshing skills.

[JohnRobHolmes]

How much room do you need? The clod gears take up a lot of room on the shaft. You could get away with using another shaft though, like a drill blank.

[DKNguyen]

I need just enough room to square or flatten a side of the shaft a little bit to mate it with a shaft coupler. It's not load bearing so it doesn't need to be very much...5mm? I am talking about the 5mm pinion:

http://rc4wdstore.com/product_info.p...roducts_id=481

Not the long RC4WD pinions that would take up most of the shaft (that is, unless you can get them with 5mm bores. I'd just rather have a stronger shaft and a regular gear than a really strong gear and a thinner (lathed) shaft.)

Custom shaft eh? The Hyperion shafts are just plain metal rods with some little knick milled in it all the way around?

I also just read your Revolver Hyperion Comparison. Very nice. Do you have more detailed descriptions or experience with the so-called "hunting" of the poles when the motor revs up? It's one of the unpredictabilities that has made me want to go with the much more cumbersome sensored commutation rather than sensorless (it's really hard finding some type of small compact absolute encoder that can fit onto an outrunner or fit onto a Clod gear box!) I just really like the idea of being able to lock on and startup right at zero speed. Do you have any idea the minimum RPM a Z3025-12 needs to spin to generate sufficient back EMF for the sensorless circuitry to detect the pole?

[JohnRobHolmes]

You really ask the hard questions! First off, unless you are successful at making the motor sensored, it will crawl horribly with a 5mm pinion because of the faster gear ratio. If you are successful at this, I will give you HUGE props! A sensored outrunner would be pretty awesome.

For a repacement shaft, #9 drill blank rod is damn near a perfect fit. Not any play in the bearings at all.

For the sensorless motors, only the worst construction makes the esc "hunt" for a good pole. This will not happen with a Hyperion. The mamba starts it up consistent every time. You would need to have a 6 or 7 tooth pinion to go really slow though, as Castle hasnt made any progress on slowing down the minimum speed. I have found the min RPM to be around 4000 to 5000 "switches" of the controller per minute. The hyperion is 42 switches per revolution, so this is around 100-120 rpm. I talked to the owner of Castle about this for about 20 minutes last week. He spoke of increasing the buffer underrun (overrun?) and increasing the bit rate of encoding to remedy this. We also spoke of controlling the motors like a stepper motor, but PWM or chopping would be needed to keep the motor from smoking instantly. I really hope Patrick decides to use stepper control, which is non-sensored anyway.

Have you considered adapting a stepper motor and controller for this?

[DKNguyen]

Odd...wouldn't a sensored motor crawl...better? Especially with a faster gear ratio since the motor is spinning even slower than normal when travelling a lot speed?

There must be more than one way to start up a sensorless BLDC then. I've only read of two ways one which was a single sentence saying to do open loop commutation until the BEMF was strong enough to detect. The other said to send an oscillating pulse to the motor to hunt down the pole.

I was thinking that the 15T 5mm pinion might require the motor to spin too slow at low speed travel for the sensorless stuff to work, but 100RPM is pretty damn slow. less than 2" per second which is probably as slow as I'd ever need it.

I haven't thought about a stepper because it's so much more convenient to go for an RC brushless since they fit into all the transmissions with minimal effort, easier to find, and are cheaper. Plus, it's very little effort for me to operate the BLDC in stepper mode anyways- just a little change in the microcontroller's coding since current sensors are already present on the motor driver. Just the inherent problem that steppers can lose synch since they are open-loop. I'll leave 3 extra pins for an encoder to see if I can get it to work and probably have sensorless on my driver anyways. (if only so I can run the motor under no load at high speed and get the driver to learn which encoder position corresponds to which winding...I certainly don't want to have to do that manually). The difference will be whether it's good for regular use or crummy for soley calibrating the encoder.

[JohnRobHolmes]

A sensored motor (servomotor) would crawl better under variable load with stepper control. If a 12 tooth/14 mag motor and controller lose synch, you would have a jump of 8.57 degrees (one phase change) per "bad" commutation. Do you have a controller that will do three phase stepper control, or is this all scratch build?

What kind of sensor are you going to use?

Some good reading if you are up for it.

http://www.cs.uiowa.edu/~jones/step/ They go through the pros and cons of servomotors vs stepper motors in the abstract.

http://www.southernsoaringclub.org.za/ Read the articles section, especially the 3rd motor writeup.

http://www.powercroco.de/

http://www.torcman.de/peterslrk/Waru...er_so_eng.html

[DKNguyen]

Scratch built. THe sensor I was going to use was an absolute magnetic encoder (as opposed to a relative magnetic encoder). The pulse width of the PWM output signal indicates the position.

http://www.usdigital.com/products/ma2/

That torcman webpage answered a bunch of questions about visualizing 12-14 motors (I can do 6-8 but that's my limit). Hard to keep track of which pole is aligned with which. IT also fixed an equation I had to come up with...my step angle was half as big as it should have been which made things really strange, hehe. THanks.