Dynamixels And Herkulex.again

 
#1

Love digging up a horse and beating it again? Well fellas I'm here to help you out!

Lets start another up to date discussion about the use of, and the support of, Dynamixels and the HerkuleX line of professional servos. I'm moving up a level with some upcoming projects and steering away from the hobby style servos. I've spent days researching, using geared stepper motors, geared DC motors as servos and have come back full circle to serial servos. Due in part, by all the unknowns and unreliability associated with creating a servo from scratch.

Tell me about your success and failures of using the Dynamixel and HerkuleX servos with EZB. Please be detailed in your experience and add something to what is already written in the prior threads about subject. What needs to change/improve for better support? Perhaps this is adding to existing plugins or writing new ones? Speaking of plug ins (this is probably another topic), but i wonder if there would be more incentive to create plug ins if there was a pay for development? Like how the app store works? Just a thought there.

I really believe in everything EZ robot and want to continue using the products, because well its so EZ and the results are amazing. I'm well aware the majority of sales is in the education market for EZ Robot and therefore guides their company. But, how can we work together as a group to build support for the next level of servos and professional robotics? And ask ourselves what is the motivation to do so?

#2

Install the dynamixel plugin and the dynamixel servos will simply just work. Easy as that.

You bet ezrobot is focused on education, and has been since day 1. Are you saying that you've learned nothing using the platform? Tongue

#3

Let's see if I remember everything wrong with dynamical plug in as I'm the one who pushed pretty hard for it to work.

So my design includes mx 64 servos , 2 for the elbow joints. These run of of Ttl logic.

Then I was using the classic ax12a servos for elbow rotation and wrist rotation. These should be able to run off of the same buss. In all the robotis videos I have seen there are all different size dynamixels including the ax12a daisy chained together and working. However....

That did not work. And still does not. I then upgraded the ax12a servos to the mx 28t to be daisy chainable. That seems to work but the resolution of these servos is much greater than Standard Servos so the positioning is way off. I will dig back thru my notes to see what else is not working correctly.

I can say with 100 percent certainty after spending 2,000 on dynamixels that there are still a lot of issues when trying to be controlled with ezb. I have a bunch of ax12a servos laying around now.

Edit: digging back a little the ax12a has a different bit resolution (8) bit? 1024 count while the mx series servos have (12)bit 4096 resolution. There was no way to control the 2 different types having the different resolutions. I could control one servo or the other. As I dig more I'll post more. This issue as well as a couple of personal issues has caused this project to stall.

#4

The way to control two different types of dynamixel servos would be the same as you'd have to do with arduino or any other platform, write some code. The native support for dynamixel servos in the ezrobot plugin does not include mixing models/versions.

The resolution can be fine tuned as well in the plugin. As mentioned in numerous threads and your thread, the plugin can always be modified to change the maximum servo position globally of the entire EZ-Builder project.

#5

@Dj,

You bet I've learned alot!

So with the plug in I should not have any issues with any of the dynamixels (as long as I don't mix versions unless i code)? Thats great news. My project will use the $500 a piece Dynamixel MX-106 servos. There are two flavors, the rs-485 ver and the ttl ver, I'm assuming the ttl ver will be the one I need?!

@kamaroman68, so you are saying that you are unable to get the fine resolution (12bit) with the EZB? I assume it defaults to the 2 degree per step in EZ builder? Have you tried getting this controller and have the EZB control it?

http://www.trossenrobotics.com/p/arbotix-robot-controller.aspx

I like the HerkuleX but its a lot of plastic (horns, gears etc), the Dynamixels have an all aluminum choice. My project will have to be continuous duty for 52 weeks out of the year, and these servos offer warranty as well.

#6

What do you mean by "2 degrees per step in EZ-Builder"?

#7

Sorry max pulse width of 2 MS or 180 degrees max. Some of dynamixels travel 360 degrees and the HerkuleX have 720 degrees at 12960 steps of resolution.

#8

Dynamixel doesn't use the same protocol as a pwm servo. So the degrees isn't related to the pwm (pulse width). What you configure the plugin to scale for degrees will make the actual values different.

#9

I guess all I am saying is ... although watching trossen videos of mx64t and mx 28t and ax12a all being controlled on the same buss I was unable to do so. So I upgraded ax12a servos to the mx28t servos so they shared common resolution (12) bit 4096 counts. I guess I was misled by the trossen videos. As to coding plug ins Im not there yet.

#10

Ok well I've placed an order for both servos and control boards. I'll report back on my results when I get them running in virtual servo mode. Hopefully I can get these working.