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View Full Version : Why is MX-28 more expensive than RX-28?



jwatte
09-28-2012, 12:22 AM
Looking at the specs, the RX-28, at $209, seems in all ways superior to the MX-28, at $229.
What am I not getting?

Th232
09-28-2012, 12:44 AM
In terms of speed and torque the RX-28 looks better, but I'd say that the control of the MX would be better with the magnetic encoder and all. Wonder how much a good magnetic encoder costs these days. Similar situation with the EX-106 vs MX-106, but interestingly enough not for the RX-64, the MX-64 is specc'd for both better speed and torque.

tician
09-28-2012, 01:22 AM
The MX-series servos, with 360 degree 12-bit magnetic encoders, 32-bit 72MHz ARM Cortex-M3 controllers, and up to 4.5Mbps bus speeds with your choice of bus interface, are far superior to the RX/EX servos, with ~300 degree 10-bit potentiometers, 8-bit 16MHz ATmega88 controllers, and only 1Mbps bus speeds with only RS-485 interface. The only real disadvantage of the MX-series is the slightly lower operating voltage range, and I think that is mostly because of the use of 11.1V LiPo's in all their kits.

The magnetic encoder used in the MX-series servos runs about $12 each in small quantities (Austria Microsystems - AS5045).

Now back to not writing the 1000 word Perspective for "Research Methodology" due in ~6 hours that I've known about for over two weeks and still consists of 0 words (barely have a title and no real hypothesis) (also have to give a 4 minute talk on said non-existent perspective).

jwatte
09-28-2012, 01:46 PM
I see -- the sensor and control circuitry is better. Thanks for pointing that out!

It's a shame that the MX-28 is specced so much lower than the RX-28 for torque and, especially, speed, though, as this series seems to be the next logical upgrade if you run out of capacity on the AX-12s. Btw: That sensor looks fantastic! And you only need to buy 2,000 of them to get them at $5.
Not that I have the $5,000 for a set of 18, but I'm starting a monthly set-aside...

Research methodology? I suggest you learn from the best, i e Congress:
1. Decide what you want to be true.
2. Look around until you find someone with the title "professor" who supports you.
3. Pay and promote said professor.
4. What you want is now true!

tician
09-28-2012, 02:22 PM
~$200 for 18 from digikey.



Research methodology? I suggest you learn from the best, i e Congress:
1. Decide what you want to be true.
2. Look around until you find someone with the title "professor" who supports you.
3. Pay and promote said professor.
4. What you want is now true!
The rep for my district (http://politicalcorrection.org/blog/201003190002). ಠ_ಠ

I need to build it an asylum (http://www.terindell.com/asylum/docs/asylum.html).

lnxfergy
09-28-2012, 06:00 PM
The only real disadvantage of the MX-series is the slightly lower operating voltage range, and I think that is mostly because of the use of 11.1V LiPo's in all their kits.

I think of this as actually an advantage across the whole MX series -- the older RX series ran at different voltages, and so it was very difficult to mix different RX series servos and actually get the full torque/speed out of them. The new MX series is basically all designed for 12V busses -- which means you can actually just slap whichever servo you need in. The new brackets are also pretty much able to connect any MX servo to some other MX servo without too much difficulty.

-Fergs