Well, summer is over and it's time to get back to work. My team has
been busy the last few weeks attempting to finalize the selection of
components that will comprise the motor controller circuit. Here's
some of the pieces that we're considering right now:
Current Range - 0-6A
Max Cont. Current - 6A
Voltage Range - 5-45V
This Sounds like a good start , but I would recommend MOSFETS instead of
the integrated Hbridge.
4 Mosfets can easily handle the 6 amps and if the user later wants to add
a heat sink or fan he can go to 20 or more amps. Cost is about the same.
I think the PID could be nicely integrated into the PIC 18f2431 at 20Mhz
and if the PIC is fild programmable then the user could change the PID
I think 24 Volts at 20 amps will support better than 95% of Amateur robot
OC Systems Team wrote:
Thank you for the responses. We will be sure to check into your
Since this project is based around the requirements of our customer,
and since our customer IS robot hobbyists and enthusiasts, I want to
make sure I have the okay from you guys before I go ahead and change
something. Two of our specs for the controller are as follows:
Maximum Motor Supply Current: >5A
Maximum Motor Supply Voltage: >=48V
The 48V requirement was set due to a suggestion from an early post in
"Finally, I note that there are some attractive motors
rated for 48V (see the Maxon catalog). If you are going
to tackle the high-end, maybe you want to push your
maximum Voltage rating just a bit higher." - G.W. Lucas
It was also mentioned in the same post, however, that most hobbyists
would never need that much voltage. Which brings us full circle to a
more recent post:
So then, in order to officially change the customer requirements of
our project and proceed with prototyping the controller, I would like
a few more opinions on the matter.
WOULD YOU LIKE OPTION A, OR OPTION B?
OPTION A - Maximum Motor Supply Current: >5A
Maximum Motor Supply Voltage: >=48V
OPTION B - Maximum Motor Supply Current: >=20A
Maximum Motor Supply Voltage: >=24V
Thanks again for your time. My team is looking forward to prototyping
the "motor controller of your dreams", but we want to make sure we
have all the right pieces to work with from the start.
In my 20-something years of building hobby robots, I have never
used, nor have any of my buddies used a motor at more than 24 Volts DC
(Except a 190 Volt DC scooter I built. Wheee!!!!)
I think you would sell a LOT more with the higher current, lower-Voltage
Be sure you understand what you mean by 48 V. For example, if I take four 12
V lead-acid chemistry batteries to make a nominally 48 V supply the voltage
can be as high as 72 V (18 V per cell). If you look into this further you
will find there are many 'saftey' issues with such a system (sorry, I don't
have a good reference to suggest). If you are skeptical about this take a
look into telecommunication systems designed to be powered of 48 V lead-acid
batteries (as a backup), and thier safety requirements.
So, my advice... stay the heck away from 48 V. A nominally 24 V lead-acid
battery supply can be as high as 36 V which is still a 'safe' voltage.
Still not convinced? From a practical point of view, you will have little
trouble finding ICs that work in a 36V maximum system, but you will have
great difficulty finding components that work in a 72 V maximum system. A
good information source with all the technical arguments for the automotive
industry transition to 42 V maximum voltage system would be useful
I would point out that the automotive industry uses a 14 V per cell maximum
voltage whereas the telecom industry uses 18V. I can't explain why... but
the telecom guys have been playing with high voltage battery systems far
longer so I'm sticking with the more conservative (18V) number where safety
is concerned (because I'm not smart enough to know better).
Note the statement that 60V dc is the maximum 'safe' DC voltage.
I have a vaguememory that the 18V per cell condition may occur when cells
are being charged(which in telecom is whenever the AC power grid is ok).
But, its only a vague memory.
Thanks again for the responses. It looks like you guys are pretty
unanimous about the lower voltage, higher current requirement. This
really does help us out because we were spending a whole lot of time
trying to find the higher rated power components while still staying
within our price range for the end product. Also, since this is our
first experience with the motor controller market, staying away from
"unsafe" voltages is probably a good idea.
It is our goal to finalize the component selection of the controller
by Wednesday of this week. I will post later this week with each
component and a bit of reasoning as to why we decided on it. Thanks
again for the help.
Does anyone have any history with the LS7266R1 encoder to
microprocessor interface chip? Specifics on the chip can be found
The US Digital website states the following:
"The LS7266 has two functionally equivalent halves, the X side and the
Y side, selected by a dedicated input pin Xnot/Y (pin 17). Each half
is a completely independent counting system."
Can I take that to mean that only one package is needed to decode two
seperate motor signals, or will the quality of decoding be decreased
at all if I attempt that with this chip?
We have finalized the main component selection for the motor
Now that we have our main components pinned down, we'd like your
opinion on a smaller detail:
What kind of interface connections would you like to see on your motor
controller circuit board?
The motor controller circuit board will need some sort of external
connection for the following signals:
Battery (PWR, GND)
Motor 1 Decoder (PhaseA, PhaseB)
Motor 2 Decoder (PhaseA, PhaseB)
Motor 1 PWM (PWR, GND)
Motor 2 PWM (PWR, GND)
So there will be a total of ten external connections. The previous
design of the controller circuit utilized male clip connections on the
circuit board with female connectors from the battery and motor
signals. We want to make sure that our design is as functional and
adaptable as possible. Basically, we don't want to put a certain type
of male connector on our board if you guys don't usually use the
required type of female connector. Should we just leave empty pads on
the board for your own installation? Or would a wire clamp connector
be a good idea?
We really want to make this board as pleasing to you guys as possible,
so please let us know what you would like.
I would like to explain why my team decided to go with the MC33186DH1
h-bridge instead of the MOSFETS as recommended. The main factor in
this decision was the overall safety features of the h-bridge chips
compared to the MOSFETS. Since this is our first motor controller
design, we decided that it would be better to go ahead and prototype
with the MC33186DH1. However, we will definitely keep the MOSFETS in
mind for future implementation as the project progresses.
The chip is designed for two quadrature encoders, but in all cases
(regardless of the decoder chip) the usual precautions against FRI and
power supply noise applies.
Author: Robot Builder's Bonanza
Actually, there's been a bit of a change in the final design. Due to
some last minute ideas, the LS7266R1 decoder chip was tossed out of
the design and replaced by a second PIC18F2431. Since each PIC
possesses a single quadrature encoder interface (QEI) we will use
dual-processing in order to perform accurate, synchronous motor
functions. So the new concept looks like this now.
So now we have a new question for you:
What type of microprocesor interface do you prefer to use in your
We will most likely use the SPI function of the PIC processors to
communicate internally, but we will also have external processor
connections in order to program and accept instructions from an
external processor (i.e. your processor). Some of the more common
interface types that we have run across during our research is I2C and
This week my team will begin to build our first prototype. We are very
excited to finally begin working hands on with our project, and we
appreciate the continued feedback that you have provided for us.
And here is yet one more recent reference. This one is about the 42 V
systems for cars, with some specific statements about the challenges that
42V systems present for electrical components. It also has some specific
statements re: safety issues.
Even if you aren't interested in 42V battery systems I would still recommend
checking out the website. Many intitiatives in cars have direct connection
to robotics and this is a tech oriented site.
link to the site....
I apologize for the confusion. There was a little typo when I entered
the part number. It should be MC33186. Here is a link for the data
sheet, though, so I don't take up any more of your time unnecessarily:
Thank you for your interest in the project, and sorry about the typo.
I have started a very rough webpage documenting the progress of my
team and further detailing the background behind our project. I will
continue to add more information to the site in the next few days, and
then I will update it as we progress through the project.
Basically, I wanted to give you guys a better idea of what we're
trying to accomplish and emphasize the fact that we really appreciate
all the feedback that we have received from this group.