Ste's Robot Project - Motor and controller selection help

Thread Starter


Joined Sep 23, 2009
Hello all,

I have been planning to build a robot for ages now. I have drawing "cigeratte packet" designs for literally years, but although I am good in some areas, I am hopeless at actually picking a product off the shelf and getting a circuit going.

I am going to finally take the plunge and get buying components to build with.

I have a few questions in this topic (which i know is taboo, but they all lead on from each other)

I intend to build a modular system, where a module is responsible for a specific area's control, these modules will then be linked with a serial bus communication newtork (probably a long time in the future!)

So every journey must begin with a first step, and mine is the motors and motor control module.

What type of motor should I choose? I am thinking that a brush/brushless DC motor is the best choice to start with. I plan to strip this out of a portable car compressor pump (£7.99 from ebay). Will this be a DC Br/BrLess motor?

What type of feedback system would be best? I think that adding an encoders to gain a feedback, thus creating my own servo and design a PID to run it all. Does anyone know of some good position encoders, that are avalible off the shelf?

Would you just shell out and buy a servo?

I don't want to build my own H-Bridge, because I want an all in one package that does all the options i could build anyway, however, there are millions around. Does anyone have a suggestions of a controller they have used?

Additional transistors? will I need to add transistors to allow max unregulated current to flow to the motor, or do controllers have those built in?

So to summerise:
Will it be a DC Brush/Brushless motor in a car compressor?
Is that the right choice of motor for my project?
Are there some good position encoders avalible which will work with the above motor?
What H-Bridge controllers are good, cheap and readily avalible?
Will that H-Bridge come with "everything I need"?

Thanks for you time, and any help would be much appriciated...


Steve Mulvenna :)


Joined Apr 20, 2004
With no parameters, not much accurate input is possible.

One thing can be answered -
will I need to add transistors to allow max unregulated current to flow to the motor, or do controllers have those built in?
Nope - just pull in a relay and let the contacts pass the current.

Thread Starter


Joined Sep 23, 2009
Hey there, sorry about being ambiguous...

I am going to make a little bot, track driven approx 30cm long and 20cm wide.

stage one is to get the base together with the tracks and motors running and controllable with speed and direction. I would like to at this stage add in a PID and gain precice control over the speed and angle of the motor.

I guess that the whole thing is going to weigh around 5kg, and I would like it to have a top speed (on the flat) of 8-10mph (not really fussed about the top speed though).

<quote>Nope - just pull in a relay and let the contacts pass the current.</quote>

I am sure that the best way to control speed is with PWM, and a relay would not be suitable for the high frequencies required... I have just checked and the quickest response time i can find is 7ms and that would play havock if I was to use a 10kHz PWM frequency

Thanks again...


Thread Starter


Joined Sep 23, 2009
Hi again,

this is the type of motor controller that I want, but I don't want to build one out for discrete components.

I have heard that there are ready build IC that controlls the motor speed and direction based on the duty cycle of a PWM input. (10%DC = full reverse, 50%DC still, 90%DC full forward - DC Duty Cycle)

I have been having a look, but there are too many to choose from, and I don't know which one will do the job.

I have attached a flow diagram that may clarify what I am after:

Recommendataions on the motor controller would be great
Do I require a transistor arrary to get enough current to the motor?




Thread Starter


Joined Sep 23, 2009

That is 100% perfect, I have been trawling through data sheets for ages now, and when I find one that looks ok, it is normally too expensive.

This one is both in stock and reasonably priced. also example circuits in the data sheet are good.

Thanks a lot.

I will now be researching LIN bus controllers, LIN bustransevers and simple microcontrollers...

Thanks again.



Joined Sep 26, 2009
Try the LMD18200T by national Semiconductors >> << I use this in plenty of robotics and motion control, the LMD18200 accommodates peak output currents up to 6A. An innovative circuit which facilitates low-loss sensing of the output current has been implemented also so you will be able to tell when the motors stall, it only requires a TTL compatible input for Brake, Direction and PWM.....

I used this H-Bridge to develop a 2 speed PWM driven PM DC Motor controller (for this company for their automated recycling machines. I also use another variation of the same H-Bridge without the current sense output the LMD18201T....

My .02
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