Pagin JetJock: Servo motor info

[figgie]

JJ

got a question for you regarding servomotors.

most servo motors used in DBW throttle application get driven directly from the sender motor on the pedal.

There is a car that does not do that. In particular this car has the sender but the signal goes to a CAN bus and that then gets sent to the DBW which in turn turns it into throttle plate position.

So the question is (and I think I know the answer). The servo motor should still be the same as before but now has a CAN reciever module built in. If the schematics are shown. Can the CAN reciever portion be bypassed and have a PID controller directly attach to the DBW motor?

-figgie

 

[jetjock]

We're talking true servo here and not a stepper right? Since PID is analog it can't be connected to a stepper. Not that PID is suited to servo control anyway. I think what you want is is a true servo loop which is not PID in nature. At any rate you'd need a servo amplifier between the controller and motor. Something to drive it. Usually done with a matched set of complimentary power transistors and a circuit to handle the encoder. It's not a servo loop without feedback. Does that help?

 

[figgie]

JJ

it does.

I need to be specific with what this is.

Motec + BMW V10 engine (M5).

It has two DBW throttle on it. In stock configuration. The ECU controls the DBW's over the CAN bus and it is a true servo. Though it has the CAN module built into the servo motor circuit so I am deciphering that. Of course BMW won't release that information but being an electronic component. Not to diff to find out HOPEFULLY!

 

[jetjock]

Ja, German engineering

Ok, I thought you were trying to connect an older analog PID controller to a servo. So is the Motec throttle output analog or digital? Does it have an input you can use for dealing with throttle actuator position? A quick look at the Motec site says some of their boxes will do OEM throttle control for Bosch systems. That kind of suggests it supports CAN. Have you talked to them? Which model do you have?

 

[Ckanderson]

mercedes are the same way... i know my CLK 430 does this.

And FWIW I hate it.

When i floor it, i want full power, i dont want to give it half throtle, and have it open the throttle 90 percent. i HATE that.

 

[figgie]

Ja, German engineering

Ok, I thought you were trying to connect an older analog PID controller to a servo. So is the Motec throttle output analog or digital? Does it have an input you can use for dealing with throttle actuator position? A quick look at the Motec site says some of their boxes will do OEM throttle control for Bosch systems. That kind of suggests it supports CAN. Have you talked to them? Which model do you have?

the motec can support DBW natively without CAN chatter. They have a product called the DBW4 that allows the motec to control 4 servo motors by communicating to the DBW4 via CAN. Otherwise it the motec m800 can control the DBW directly with analog outs.

Though they said the BMW M5 does it over CAN and motec has not broke that code and from talking with thier engineers, they are not going to try (Damn FlexRay!!). BUt being in computers myself. This looks like a simpler version of the ethernet standard for network. Slower (1Mb/s) and more chatter.

 

[3p141592654]

CAN has some twists over Ethernet that make it a bit tricky. In particular, CAN prioritizes traffic (obviously important in a real-time system like a car) by implementing so-called bitwise arbitration to handle collisions. Timing is also done in a rather unique way since each node has its own clock, unsynchronized with any other node. But, if you are just using it at the application layer then its straightforward.

 

[tte]

How many wires going to your CAN receiver module?

Cheers,
Roy