I am building my first robot, and since I aim for a rather heavy robot (10 kg) I will need powerful motors. I have found 2 DC motors with 5Nm nominal torque, which should be enough I think, but these pull 3 amp nominal, with startup and stall peaks up until 17 amps. I want to drive these motors with the dual high current motor driver from Polulu.
Now I have following question: Since I want to drive my motors with a serial port, is it possible to use the micro dual serial motor controller to generate a drive signal for the dual high current motor driver? As far as I understand, this micro controller generates a PWM output, which I guess you can use to drive a second heavier controller instead of small motors. This combination is a lot cheaper than two SMC04 high-power motor controller with feedback.
The VNH3SP30 and VNH2SP30 motor drivers take three inputs and have one output, so you cannot directly use them with our dual serial motor controllers, which give you only two outputs (per motor). We will be releasing a VNH version of our dual serial motor controller (probably in early 2007) that will allow direct control from a serial line; until then, you will need to program your own microcontroller to do the serial-to-PWM conversion. The main feature of the SMC04 is the feedback-based control, so you’d be paying for something you don’t need if you got those.
I have been thinking about a way to convert the two output signals of the micro controller to the correct three inputs for the VNH controllers. I think a simple flipflop (to generate the correct 01 or 10 combination depending on the direction of the current) and a rectifier (to rectify the PWM signal) should do the trick. Is this possible you think, or am I missing something obvious or less obvious?
I suppose that sort of thing could work (OR gate between the two PWM outputs to get the one PWM for either direction would work). It seems like an inefficient solution since you can get a microcontroller with a hardware UART and PWM for under five bucks for just about any 8-bit architecture. That way, you could also PWM faster, use the current sense, and so on.
But I guess it’s quicker to try a few flip-flops and or gates. If you try it, let me know how it works!
I agree that this is not the most efficient or cheap solution, but I have several reasons why I want to do things this way:
The micro motor controller is not so expensive either.
It has a nice interface, already programmed in the controller, and with source code for linux available, so there is almost no low-level or PIC programming required.
It works together with the pololu servo controllers, which I would like to have on the same serial bus.
So I do not mind spending a couple extra dollars (or euros in my case) for a lot less work and learning
I will let you know how it works out, but I still have to order everything, so it might take a while before everything is up and running.
