Motors

Hello all,

I need to "soup up" the motor outputs from the H-bridges in some way to allow them to control battery drill motors which can apparently draw up to 20A running and 60A stalled!!  Whether or not these figures are correct I don't know.  I was thinking of using MOSFETs as they can switch large currents. However, how would I connect them to the motor outputs???

If anyone has a better idea, let me know.  Nothing has been finalsed yet, including the motors, so if there is a better motor/gearbox combo i can use let me know!  It is for a fairly heavy floor-trundling robot which may get outside at some point, so would need powerfulish motors if it got onto grass.

Thoughts/criticism/ideas??

Cheers,

Moosey

I would use MOSFETs to drive the motors. If you end up doing this its not a bad idea to send the outputs from the controller to some optoisolaters, which will completely isolate the controller from the power network so that there aren't any voltage spikes coming back into the controller.

IGBTs can also be used, but usually are used in extremely high voltage/current situations (think like 250A industrial motor), and they have a larger voltage drop i believe, which is negligable in a high voltage environment, but in your situation, would cause more power to be consumed than MOSFETs. (Also i think there switching speed is not as fast)

Make sure you rate the transistors well over the range that you will be using, since the max current/voltage given for the package/transistor are pretty much the breaking point, and will cause them to wear out over time much faster if they are put in that range.

I would also put somewhere in your logic a stalled function, when if the motor is not moving under maximum current over some time period then to cut it off, so you can save power.

This can be implemented in a PID control somewhere if you are using it. (PID = Proportional Integral Derrivative = Controlling the power based on how the motor is performing).

Previously Kevin Grant wrote:

I would use MOSFETs to drive the motors. If you end up doing this its not a bad idea to send the outputs from the controller to some optoisolaters, which will completely isolate the controller from the power network so that there aren't any voltage spikes coming back into the controller.

<snip>

Make sure you rate the transistors well over the range that you will be using, since the max current/voltage given for the package/transistor are pretty much the breaking point, and will cause them to wear out over time much faster if they are put in that range.

<snip>

Yep, I thought of using the MOSFETs.  I don't get how to connect them though as the motor/PWM outs on the board require a current to be sinked as well as sourced.  Optoisolators are a good idea I suppose. How do I connect the MOSFETs?

Cheers,

Moosey