PDM: M400 PWM and CAN addresses

[Rex Chan]

Hi MoTeC, I am from the Melbourne Uni FSAE team (MUR 2010). This year's team are interested in getting an M400 and PDM15; I have some questions relating to how we could use them.

We would like to use the M400/PDM15 combo to power, among other devices, a DaviesCraig EWP115 (10A max) and thermo fan (10A max), via PWM to control their speed, based on engine temps. We can get the M400 to send PWM signals from the AuxOutputs, but obviously don't have enough current to power all these devices. Can we use the PDM? I can't find the max switching freq in the user manual, and the sample PDM file has switch delays of 0.10s. We could use a DHB, but they are expensive, and considering we already have the PDM, will introduce more parts that could fail.

The second question relates to how to setup the M400 and PDM to communicate with each other. The PDM lets you configure where to look on the CAN bus for data (base address, offset, hexmask, etc), and the M400 can be setup to send on any base address. However, it sends a preset list of values. How do I know where to look in the CAN data for the value I want? Is there a list somewhere? For example, I we can set the M400 to send the "ADL Dash Logger" data set, which contains ET, RPM, etc, but I don't know how to set up the PDM to read these.

Thank you very much for your help.

[Holmz]

...I can't find the max switching freq in the user manual, and the sample PDM file has switch delays of 0.10s. ...

Rex

25Hz max...
http://www.motec.com.au/forum/viewtopic.php?f=17&t=1106

[DarrenR]

Hi Rex,

Holmes is correct, the highest frequency the PDM outputs can switch at is 25Hz.This can be achieved but using the flash operator with on and off times set to 0.02s (the minimum times) giving you 25Hz at 50% duty. This can be used to give a 'half speed' operation, but this is not recomended if the motor is drawing close to the maximum current, not so much for overloading the output, but just the amount of electrical noise this creates.

The correct method is to use a DHB, or you can use a solid state relay (check the switching times) or even get someone doing electrical engineering to setup a mosfet (switching ground) for you.

As for the CAN setup, read the attached doc and if you have any further questions let me know.

Cheers,

[Rex Chan]

First, thanks a LOT for that document - it's helped us out greatly to get our initial PDM config file setup! Is there a MoTeC page where all the DTN#### pdf's are availiable?; seems like the only way to get them is via links in these forums?

Second: we're going with a solid state relay (SSR) to regulate our motors (power from PDM15 and PWM signal from M400). I'll let you know how that goes.

Now for some more questions: we are only running an M400 and PDM15 (no ADL or SDL until next year, maybe). We've set up sending ECU CAN data to the PDM. However, we would also like to send CAN messages from the PDM to the M400. The main reason for doing so is to monitor PDM outputs through the ECU Manager screen when running the engine on the dyno. We have found that running both the ECU Manager AND PDM Manager at the same time, on the one PC with one UTC, doesn't work smoothly. We were also hoping to get warning messages on the ECU Manager screen if there were problems with the PDM outputs. Additionally, until we get a proper logger, we will be using the M400 to log data.

I can see where to configure CAN out messages in the PDM software (default messages over 6 CAN IDs, and 4 custom CAN ID messages). However, we can't work out how to receive these CAN messages in the ECU Manager:

Under CAN setup, there are 7 settable CAN IDs. The only option to choose what comes over that CAN ID is under CAN # Data, and in the current, software, there is no PDM option. We think that it may be possible to use the ADL Receive option, but I'm not sure if we can set up the PDM to mimic the ADL CAN outputs. It appears that the ADL Receive template uses compound CAN messages (and using Bit Masking), and I'm not sure we can do this on the PDM. Even using this method, we would be not fully using all the CAN out messages on the PDM (10 CAN IDs in total).

Anyway, it seems like the easy way to allow the M400 to receive data from the PDM would be to have its own template/option. Does this already exist somewhere, or if not, is it likely to be availiable in the future?

Thanks for reading my long post, and hopefully CAN happiness will result!

[JamieA]

There is really no way to get the PDM CAN messages back into the M400. The adjustable CAN transmit messages in the PDM software is only new, and was intended to help primarily with PDM to PDM comms.

The M400 hasnt really been updated to allow for this new PDM feature, and I am not entirely sure when that would happen.

At present, the only way I can see you being able to send information from the PDM to the ECU is to use an unused PDM output, and wire that to an ECU switch input... Not exactly high tech, but it would work.

regards

Jamie

[DarrenR]

Using the new CAN transmit messages from the PDM you should be able to transmit 6 channels from the PDM back to a M800. I only say 'should' because I haven't physically tried it.

Setting the M800 to receive messages from ADL and ECU2 allows you to setup two messages in the PDM to send data. Match the CAN receive addresses in the M800 to the CAN transmit addresses in the PDM. Don't forget to do the conversion from Hex to decimal.
The data you send must be as follows-

Message 0 -
Channel 0 - Blank
Channel 1 - Blank
Channel 2 - Blank
Channel 3 - Channel 1
Channel 4 - Blank
Channel 5 - Channel 2
Channel 6 - Blank
Channel 7 - Channel 3

Message 1 -
Channel 0 - Blank
Channel 1 - Blank
Channel 2 - Blank
Channel 3 - Channel 4
Channel 4 - Blank
Channel 5 - Channel 5
Channel 6 - Blank
Channel 7 - Channel 6

The channels that are left blank must be that way.

The data will appear in the M800 as input sources ADL 1, 2 and 3, and ECU2 1, 2 and 3. These can be assigned to channels and calibrated accordingly in the input setup.

Hope that makes sense!