Re: New Speed Controller Announced
 

eBay! Just because Victor 884s might not be allowed in FRC in future seasons would not mean they've lost all use. They are really good speed controllers, and there are always other people (especially Battlebots community) who would buy them.

Gone are the days of giving the electrical and controls people a cubic foot of space and telling them to make it work... :rolleyes:

Re: New Speed Controller Announced
 

Obviously your mechanical people have been spoiling you. They have been giving you far too much volume ;)

Re: New Speed Controller Announced
 

I would be inclined to say that these controllers use the standard R/C PWM wiring scheme the Victors employ, seeing as a) the digital sidecar for the new system has standard PWM outputs and b) the PDF explicitly states it uses the standard R/C PWM servo interface.

Re: New Speed Controller Announced
 

Since when is big the new small? First the radios, then the maxi breaker panels & distribution blocks, then the new control system, and now the speed controllers...

Re: New Speed Controller Announced
 

I have been estimating 6 lbs and about 1/2 cubic ft. for the control system alone. You can back into the size from the picture knowing that the pin spacing on the header is 0.1 inch or judging the two RJ 45 jacks. I am guessing that it is at least 1/2" wider and 1" longer than Victors.
16kHz is still audible to students and I can tell you from experience that 15,734 Hz is annoying to anyone under 50 and some over 50. I question the choice of switching frequency vs. the inductance of the motor windings though. Testing will confirm this.

Re: New Speed Controller Announced
 

Maybe more teams will use the old Victors, they are still available.

It's beginning to look a lot like Christmas...
 

The flyer (pdf) I read said 20kHz. Am I mistaken?

As to claims of linearity, that depends on what you mean. The output may actually be very linear, but the system need not respond in a linear way.

My experience in automotive systems is that when you go from low PWM freq (100-400Hz) to higher PWM freq (10-20kHz), the motors do not respond the same, especially at low duty cycles.

For example, if, in order to get a system moving, we needed say 20% duty cycle at 100Hz, we would need to bump the duty cycle up to 30-40% at 10kHz PWM freq.

This was very puzzling but we eventually attributed this our mechanical system's time constant. At 100Hz, the mechanical system's time constant was such that the system had time to react during a single PWM pulse -- These "full on" pulses provided a kick to get the motors and gears turning. At 10kHz, the system can only react to the average not the individual pulses, so it required more on time to get things rolling.

It does not say in the flyer but I hope that the H-bridge is configurable in ways that are feedback loop friendly. What I mean is that you can drive motors via an H bridge in several ways.

1. ON = 12V, OFF = Open Circuit
2. ON = 12V, OFF = MOTOR LEADS SHORTED
3. ON = 12V, OFF = -12V

#2 is very nice for feedback control of large arms for example.
#3 sounds very strange at first, but it can provide some very nice control features as well (thought it can be tough on the electronics) in this case

• "OFF" for the motor is accomplished by outputting 50% 12V & 50% -12V.
• "50% Forward" is accomplished by outputting 75% 12V & 25% -12V.
• "25% Reverse" is accomplished by outputting 38% 12V & 42% -12V.

As I said, it seems strange but it has some very nice behaviors. This type of control is called locked anti-phase motor control and I discuss this issue at length here

Once they implement CAN, I hope that they also consider some other control friendly strategies:

• using current messurements to allow for velocity (and even position) control without the use of encoders or other sensors. I discuss this here: What Dr Joe Wants for Christmas... (Man, I love referencing myself ;-).
• implementing PID control onboard the speed controller (send it your gains and from then on just give it a desired position -- let IT figure out what the PWM outputs should be)
• Diagnostics, diagnostics, diagnostics. At a minimum teams will know if a speed controller has become unplugged -- I guess that feature alone would have changed the outcome of about 20% of the FIRST tournaments ever held. But open your mind a bit and you can imagine diagnostics that tell you if your motor is overheating, if your mechanism is binding up, if your wheel treads need to be replaced, etc. etc. The mind reels at the possibilities.

It is only August, but it is looking more and more like Christmas to me...

Joe J.

Re: New Speed Controller Announced
 

I notice that this press release comes from Luminary Micro, and not from FIRST. They are bold enough to announce that they "will be included in the FIRST Robotics Competition's (FRC) official Kit of Parts (KoP) and distributed to over 1,700 teams in the upcoming 2009 international FRC." This "announcement" has not yet been acknowledged or confirmed by FIRST. But I have heard rumors that the content for the 2009 KOP, and the associated rules about what is legal to use on the robots, have not yet been finalized. Therefore, I would surmise that this announcement may be a bit premature.

I have heard tales of some members of the GDC that are devious enough to pull an item out of the KOP specifically because the community got unauthorized advance knowledge of a part, and started to do pre-design and pre-build work before the season officially started. After all, wouldn't it be interesting if the entire community got all spun up about a rumored new "capability" that was then never actually included in the KOP? That would be an excellent way to divert their attention away from what was actually going to happen.

Nah, something like that would never happen. :rolleyes:

-dave



.

Re: New Speed Controller Announced
 

I weary of the new system just because it is new, but a lot of these features are very interesting to me. I'm really interested to know more about the sensor feedback.


Brandon, can you ban his account? Please....?

Re: New Speed Controller Announced
 

One thing that I noticed (and do not like) is that there is no ventilation for the drive MOSFETs or etc inside. Driving 20amp motors will get them warmed up and those look like they will be nice and toasty.

Re: New Speed Controller Announced
 

Joe,
I was referencing a previous post with the 16 kHz. At this and higher frequencies, the combined inductance and series resistance will produce a low pass filter that will serve to limit rise times and produce triangle waves instead of the the expected square waves. Glad to see you back on the forum.
Perhaps Richard, if you are reading this, can give us a handle on motor winding inductnce. I would think it would be pretty high, on the order of 100 mH. I won't be able to do any measurements for several days.

Re: New Speed Controller Announced
 

While the new control system (including these speed controls) is more capable than the old one, the increase in physical size is a lot. We would not be able to comfortably fit these components on any of our previous four robots.

Re: New Speed Controller Announced
 

Where did you "notice" this? It's contradicted by the Jaguar's reference sheet, and the ventilation grille on the top is recognizable as such in the posted image.

Re: New Speed Controller Announced
 

From the tech at the Luminary booth here at NI Week.....

-full current sensing and feedback for position control, when they unlock the feature in '010
-onboard PID, you tell it the constants and it goes to work

The unit has a cool limit switch feature also built in. you can wire a limit switch directly to the esc for both directions of operation as a built-in software stop.

The standard pwm connection still applies for now. the CAN interface is either disabled or now allowed for our use, though the demo unit they were running was linked up via ethernet cable. looked pretty slick.

Woody said we'd be able to use victors this season to carry us through the transition. The most exciting news, is that both the FIRST rep and the NI rep said the price point for the Jaguar was going to be significantly less than the victor....."we'll be happy" were his exact words!

Re: New Speed Controller Announced
 

Any chance you can post some real photos of it with something for scale (a dollar bill)