help with some basic motor control questions??

[jaydag71]

I have a few questions regarding a motor control design I am trying to accomplish. Elements of the design have been 'scooped' from various places, ie. the h-bridge design I basically copied from an old radio-shack RC truck I had kicking around which had similar power specs to what I am trying to do now.

The posted schematic in PDF format is not complete due to the feedback circuit is not included. or that portion the basic approach I want to try splits from the transistors outputs to motor, each signal runs through a resisitor and then into an op-amp (lm358?), and onto the ADC in the PIC I am using to control the lot.

The final project is a RC platform re-designed, I'm using the posted H-bridge for the main motor and a smaller transistor h-bridge for the steering as well. I want to try the lm358 so I can use half for the motor feedback and the other half for the steering feedback? Any flaws with this basic idea?

I am also curious as to the method of control implemented originally in this design (h-bridge posted), I have a feeling that it was not PWM'd, so am wondering if I am going to run into issues when I try to use PWM for driving this H-bridge?

Any tips or hackling is welcomed, thanks in advance, jd

 

[jrz126]

Hmm, that H-bridge looks kinda funny...I would think T3 and T4 would need to be connected to a supply voltage? I could be wrong though, I always use mosfets for my Hbridges.
I saw this Hbridge on another forum:
**broken link removed**

What are you looking to get from that feedback circuit?

 

[jaydag71]

Here is the updated version of the schematic with both h-bridges and feedback sort of finished- the values are not completed on the feedback circuit as I have not calc'd them out yet- I have always had a hard time with math aspects of everything!

Anyways, I do have a TON of related motor control design questions but am going to start a new thread for them as it will be a long one, so please check it out too!

-- The feedback circuit is intended to allow calculation of motor speed only (as I have looked through the code from the project I am 'borrowing' this portion from.) the outputs from the op-amp run into the micros adc. The results are used to compensate on inclines, and functions similar. I want to use same for rear drive motor but for the front h-bridge I want to use the resulting values to only detect when the motor is starting to 'stall' from hitting the end of its 'throw' in the cheapo servo I'm using (it is a typical radio-shack servo,, small dc motor and useless mechanical pot) The pot does not shut the motor off when the end of its throw is reached, nor does it allow proper monitoring of the servos position so the goal is to couple the servos built in devices with a bit of software from the feedback to better manage the steering of the 'bot', help save a bit of battery at the same time, etc.

any tips would be great- method to cut back on hardware and accomplish same result? Thanks in advance, jd

 

[artem]

see AN894 from microchip for details :
https://ww1.microchip.com/downloads/en/AppNotes/00894a.pdf

or if you would like to detect stall condition try to check current when winding is energized .

 

[jaydag71]

Thanks for the reply, I have been reading through that particular appNote and a few similar from the microchip site-- They are excellent as a source for design infos but being a 'mostly' hobbyist who is self taught thus far, I have a hard time with interpreting the math involved!! I know that is a sad thing to admit but is the truth for me, and also the largest thing holding me back from making a career out of electronics! I guess its back to the basics for me,.... really in the end it is almost impossible to design proper electronics, read through the component datasheets and such properly without having the foundations handy!!

In my particular case I often resort to searching for the best possible online sources for 'dumbed-down' equations and step-by-step tutorials, etc, bookmark or download the content and always keep it close for when I need to figure stuff out-- lemme add that it is by far not an optimal system and often results in sluggish progression...

anyways, thanks again for the tidbit, I guess I'll end with asking for any advice about good sources for learning the foundations online with step by step examples and not miles of droning explainative paragraphs??

 

[artem]

imho, all design challenges are divided into 2 parts :
- those that are available to repeat due to someones contribution to hobbies community
- and the rest which are business related and generate money. These are mostly more complicated than above and requires either enough degree of competence and often involve math and other science knowledge

Position sensing is about latter.
Unfortunately i dont hold the key from the room where Aladin's Lamp is .)
Guess you have to dig it deeper and invest some time to study this subject.

Regards