Home made speed controllers

[NumberXVIII]

Good day everyone!

I'm an electronics engineer just starting out in the world of fighting robots, having had a fascination with them since 1998, and I wanted to ask about PWM speed controllers.

Looking around it seems that these things aren't overly complex in concept, but to get decent reliable bits of kit you need to spend a reasonable amount of money. Being in the electronics industry I have the access to the components required to make my own, But it isn't a field I've ever dealt with before SO

Has anybody got any experience with self built PWM's? Any not so obvious do's and don'ts I should look out for in my design work? This is pretty much the last thing I need to straighten out in my head before I start commit to a featherweight build and the photo/video build diary that will come with it.

Any help or advice is much appreciated guys.

XVIII

[typhoon_driver]

My advice? Unless you can build a speed controller for less than 25 quid then I wouldn't bother. Easier to buy some turnigy 85a esc and convert them

[NumberXVIII]

As far as I can tell, its only going to cost around a tenner per unit thanks to the company account with RS. I'll likely start the dev-diary later and put the diagrams on there for evaluation.

[daveimi]

Just buy one lol. I work with electronics and computers and the hassle of making a Mosfet based motor controller isn't worth it unless your building something special.

[NumberXVIII]

Fair enough. I'm struggling to come up with something I'd consider reliable, so when it comes to it, I'll buy them unless some flash of inspiration has hit me.

Cheers gents

[typhoon_driver]

I think the best way would be to get a machine going and then look at making custom parts down the line.

Oh and the only DIY controllers I know the ins and outs of use a pic chip, interfaced to an H bridge driver with the H bridge appropriately mounted

[daveimi]

Agree with Gary, use off the shelf stuff to get going and have a go with home made stuff as you go on.

[NumberXVIII]

Much appreciated gentlemen, Thanks.

[RobotExtreme]

Hi,

Since a few years, i'm trying to project my own ESC.
And until now i'm on this "project".

This year i used my own ESC to control the claw of Rabid, a FW that used a RS550 on the weapon, i tested the ESC with REAL 150A of peak and ~45A during the "holding time". None problem.

At this moment i'm using the TZ85A and the PY25A on my FW's.

I never had problems with the TZ85A, with the PY25A i burned 3...all without load, i just turned on and then, burned.

Project and make a viable ESC requires a LOT of time, money and patience

Ending this, lets start the "how build"...

First of all,

- You need a uC to convert the PPM signal from the RX to a PWM signal that will control the H bridge.

- The PPM signal have (normally) a width between 1ms and 2ms;

1ms= -100% PWM(reverse)

1,5ms = 0% PWM (stoped)

2ms= 100% PWM (forward).

- The period of this signal (normally) is 18-20ms.


I advise you to use just N-channel MOSFET's on the H bridge, for this you will need of a "pump charge" to saturate the highest side of the H bridge.

- Use a mosfet driver to control the H bridge with feedback, NEVER a "pnp/npn arrangment" (problem of the PY25A), this will burn the H bridge because the delay and "shoot-through" effect.

- If you use parallel mosfet's, use a low resistance ( 47ohm to 150ohm) on the gate of each mosfet and a fast reverse diode. The resistence to produce a "equal" saturation and the diode to a fast discharge when you invert the rotation.

I could give you a LOT of information and advises, but i don't know what you already know .



Any question, feel free to ask.

Guilherme Ferreira

[Marien]

- The PPM signal have (normally) a width between 1ms and 2ms;

1ms= -100% PWM(reverse)

1,5ms = 0% PWM (stoped)

2ms= 100% PWM (forward).

There are also transmitters that are opposite (1 ms = forward) or different bandwidth (1,2 - 1,5 - 1,8 ms or 0,9 - 1,5 - 2,1 ms)!

[RobotExtreme]

Hence o said normally,

1-1.5-2ms is a example, even with this width of pulse, if you don't use a margin in uS to reverse, stop and forward...never will stop and you run thr risk of enter in fail safe on extremes, if you program this...thr better way is use a osciloscope to measure the width of the RX.


Guilherme ferreira

[NumberXVIII]

Much appreciated. I've not got round to drawing these out yet, since the software I'll be using is only licensed to my company and work has been hectic recently. When I get round to it, I have the vague idea for the PWM mapped out in my head but I haven't yet thought about the translation between the Rx and the PWM itself. That's what I'll likely need the help with.