Resonant Frequencies

After successfully spinning the flywheel and pressure plate at 9000 RPM, I felt confident that things were looking good with the motor. I re-installed the clutch friction disk and bolted on the transmission. After spinning up the system, it started rattling and skittering across the floor around 5500 RPM. Geez. This is a royal pain.

After pondering this a bit, I tried the following experiment: I unbolted the transmission, removed the friction disk inside the clutch that attaches to the transmission shaft and bolted the transmission back on. After revving the motor up to 5500 RPM, whole thing still vibrated.

So, by just spinning the motor, flywheel and pressure plate at 5500 RPM, I get no vibration. By simply attaching the mass of the transmission (again, no friction plate in the clutch), I get vibration. Resonant frequencies anyone? I'm guessing that the added mass of the transmission brought down the resonant frequency of the system from above 9000 RPM down to 5500 RPM. There also may be some loose parts in the transmission that resonate at 5500 RPM and cause the assembly to vibrate.

I'm somewhat uncertain what to do at this point. I can put the car back together, program the AC motor controller to limit my RPMs so I never get into the resonant zone, and drive on with reduced performance. The other option is to find a new transmission (or borrow one) and see if it has the same resonant problems. Given all the effort and money I put into this transmission, I'm not looking forward to dealing with another one.

I suppose I could try adding some resonant dissipation material (like a dynamat) to as many places as I can on the motor/tranny to dampen things out. I don't know if materials like this would be able to dampen things enough. I'm probably going to sit on this for a bit... Rats.

Hub is back but EE1SpeedoDiv is not there

Today had some ups and downs. I got the adapter hub from Electro Automotive back today. I installed it on the motor shaft and, to my delight, it had less than 1 mil of runout and wobble! That's how the hub is supposed to work. I put the flywheel and clutch back on and spun them up to 6000RPM without much vibration, so things are looking better.



Before I mated the motor to the transmission, I wanted to try out the SPEEDO output on the DMOC445 that Beth at Azure Dynamics talked about in the previous post. I was really happy to hear that there's an RPM signal I could tie into. So, I got out the oscilloscope and tied it to pin 25 (SPEEDO_BUF) on the DMOC445 and spun up the motor.

Wait a minute, there's no pulses coming out. The signal is at ground. Azure said it was a push-pull circuit. The documentation said it was an open emitter output (implying a transistor that pulls up to 12V). Perhaps I didn't properly set the EE1SpeedoDiv variable in the controller. Okay, fire up the laptop and tap into the DMOC --- There's no variable remotely close to the name EE1SpeedoDiv! Argh! It's too bad that it's late Friday since the folks at Azure have already gone home, but I'll fire off an e-mail anyway and see if Beth will respond on Monday.

In the meantime, I have a (hopefully) working adapter hub and I can put the car back together and drive it. Perhaps I'll run down to Radio Shack and get an infrared emitter/receiver pair of LEDs to see if I can generate my own RPM pulses. I get frustrated when my hopes are dashed based on expectations. I guess that's just human. Ugh.

An E-mail from Azure Dynamics about the DMOC445

I recently sent off an e-mail to Azure Dynamics, the maker of the DMOC445 AC motor controller in the 914 kit. I asked how I could tap into the motor encoder signals to create an RPM signal for the tachometer on the dashboard. It turns out that the DMOC controller already has a PWM (Pulse Width Modulated) output that can be used for this. There are also some LED signals that display system status without having to use the serial port.

I would like to express my sincere appreciation for all the tech support that Azure Dynamics has provided. Beth Silverman, the support person, has been very quick to respond with whatever information she can provide from the controller designers. Here's the e-mail:

9/21/07

Hi Tim, inserted below in blue are our answers to your questions. I understand you've been communicating with Randy Pollack; is it ok if I pass your questions on to him along with our answers?

Thanks

Beth Silverman

*******************

---

From: Tim Kutscha [mailto:tim_kutscha@yahoo.com]
Sent: Monday, September 17, 2007 8:34 PM
To: Beth Silverman
Cc: tim_kutscha@yahoo.com
Subject: Re: tapping into the encoder signals to drive the RPM gauge

Hi Beth,

I hope you had a good two days off last week. Thanks for the info on the SPEEDO_BUF output on the controller. Since this wasn't listed in the Pedal_Controlled_DMOC445_User_Manual_v3.pdf file, I didn't think it was active. From your e-mail, it sounds like the SPEEDO_BUF output is active on my pedal-controller DMOC.

Feature is active on both pedal and CAN controlled

From one document it says the signal is 12V open-emitter. I'm guessing its a PWM (pulse width modulated signal) that pulls an external resistor up to 12V through a transistor. Is this true?

SPEEDO_BUF is push-pull 12V, and it is a frequency modulated signal.

Is the SOC_BUF signal also active on my DMOC445? What is the format of its output? PWM? Does it get its state from the battery voltage or does it require the amp-hour counter to be attached?

Not active

Do the amp-hour counter input/outputs work? If so, do you sell a device that I can connect to them?

Not active; we do not sell amp-hr meters.

Do the BRAKE_PEDAL,BRAKE_LO inputs work? If so, what is the proper potentiometer to attach to them?

Not used

Is there any customer useful behavior on the ANAIN3/LED_OVERTEMP, ANAIN2/LED_MALFN, NONISO_ADIO1, NONISO_ADIO2, ANAIN1 or ANAIN0 signals?

LEDs are 3.3V (unfused outputs). If an LED is connected to it, a current limiting resistor is needed.

LED0: Fault-Signal on pin 34:

- (________): off = no fault

- (_______x): one short blip = motor overheating

- (_____x_x): two short blips = controller overheating

- (___x_x_x): three short blips = motor and controller overheating

- (_x_x_x_x): continous blink = not implemented

- (xxxxxxxx): continous on = powerstage fault

LED1: Ready-Signal on pin 11:

- (________): off = controller disabled (pin 8 = low; or pin 8 = high and pin 30 = high)

- (_______x): one short blip = controller enabled, but pre-charging

- (_____x_x): two short blips = controller enabled & pre-charged, but interlocked

(for example due to gear-selector being in forward at powerup)

- (___x_x_x): three short blips = N/A

- (_x_x_x_x): continous blink = relay closed, but power-stage in fault state

- (xxxxxxxx): continous on = ready (relay closed, power-stage disabled or enabled)

The car is basically running at this point and I'm try to activate as many gauges as I can. Thanks for all your time on this.
Have a great week!

Tim

----- Original Message ----
From: Beth Silverman
To: Tim Kutscha
Sent: Monday, September 17, 2007 10:26:05 AM
Subject: RE: tapping into the encoder signals to drive the RPM gauge

Hi Tim, sorry, I was out Thurs and Fri. Are you already using the DMOC output signal -- it can be adjusted with the parameter called EE1SpeedoDiv ?? It doesn't work with all speedos/tachs, but we have had luck with the Siemens VDO "Cockpit" series, 85mm. Please see

http://usa.siemensvdo.com/NR/rdonlyres/2B56C91E-EE58-45C6-9A1B-DB89524EA0DC/0/ProgrammableSpeedometer.pdf

Regards

Beth Silverman

*************

Getting the Heater Relay and Sending Back the Hub

Rats. After putting the adapter hub from Electro Auto onto the motor shaft no less than twenty times, I'm pooped. I tried filing down several different faces of the hub to get the runout and wobble down and failed. It's going back to EA tomorrow morning for a new one. I'm thinking that attaching the flywheel shouldn't be this hard.

The flywheel and clutch assembly has been balanced by two different shops and the second shop said the first shop did a fine job, so I'm pretty sure it's not the flywheel.

The bearing on the AC24 motor just behind the adapter hub was squealing ever so slightly when I spun the motor up, so I fear the vibrations might have damaged the motor. Perhaps against my better judgment, I sprayed WD-40 into the bearing and the squealing stopped. I'll contact Azure Dynamics to see if there's a particular lubricant I should use. I thought these things were supposed to be sealed...

On a slightly lighter note, the high-current DC relay for the hair-dryer defroster system came today.

Here's the 125VDC relay. Notice the magnet in the center of the relay. The field from the magnet is used to blow out the arcing from the DC current when the contacts open up. With an AC circuit, the zero-crossings of the voltage allow the arcing to stop; not so with DC current.

Off to package up the adapter hub... (sigh).

Addendum: For those of you who wish to order one of these relays, you can get them from Newark: www.newark.com
Type prd-11dh0-12 in the search box and the relay should display (one leaded and the other lead-free).

Balancing the Flywheel...Again

I took the flywheel/clutch to Dan Halls Machine Shop this morning and just picked it up half an hour ago. Dan basically said that it was fine. He spun it as fast as the machine would go and it was only out of balance by 2 grams on the flywheel and 2 grams on the clutch pressure plate. Apparently this really isn't a lot for flywheels.

The motor adapter hub from Electro Auto still has 4 mils (thousands of an inch) runout, so I'll try to attack that next. Dan suggested that I try attaching the hub without the shaft key to see if the runout goes away. That way, I can see if I need to modify the inner cone or just the shaft key or its slot.

On a brighter note, I got an e-mail from Beth at Azure Dynamics mentioning that there was an RPM output on the DMOC445 controller that I might be able to tap into and drive the RPM gauge with (given some external converter circuit). There's also an SOC (state-of-charge) output and amp-hour counter inputs that I might be able to try out as well. There's no documentation on these pins, of course, but I'm happy that they're there to try out.

Next Up: fixing the tiny (4mil) runout on the adapter hub...

Those (Not So) Good Vibrations

Well, it's time to bite the bullet again and see what I can do about the car vibrations. My friend graciously helped me remove the motor/tranny from the car again this morning and assisted with crude vibration measurements.


We removed the motor/transmission from the car and re-attached it to the AC controller wires while on the ground. After spinning up the assembly to approximately 5000 RPM, the whole assembly started vibrating across the floor like those toy footbal players on the vibrating table.
I guess this is good because we can replicate the problem with the unit outside the car.

For those of you who aren't into car mechanics much, I'm going to use the following two terms: runout and wobble. Runout is the change in distance between the axis-of-rotation of a spinning disk and the outer diameter of the disk. Wobble is the change in distance on the front face of a spinning disk near the outer edge.


The next step was to remove the transmission and just spin the motor with the flywheel and clutch assembly attached. This vibrated across the floor as well, but not as strongly. We did notice that the tines on the clutch pressure plate wobbled around. The outer edge of the clutch pressure plate also experienced significant runout during a spin.

This actually concerns me quite a bit. The outer edge of the flywheel looks very smooth with little runout, but perhaps the person who machined off the teeth didn't get the outer edge centered well.

We then took off the clutch assembly and did some slightly more accurate measurements. After spinning the flywheel up to 9500 RPM, we let the flywheel slowly decelerate to zero and took note of the RPM ratings that we felt vibrations at. With just the flywheel, we got vibrational peaks at approximately 1500, 2900, 4400, 6100, and 7400 RPM. As you can see these are all somewhat integer multiples of 1500 with higher harmonics. The largest spread of bad vibrations existed in the 4000-5200 RPM range which correlated with the RPM of the car shaking.

After taking off the flywheel itself, we just spun the motor with the adapter hub on it (see picture below). While the vibrations were much, much less, we still felt measurable buzzing around 1700, 2600, 4900 and 6300 RPM. This is vaguely unsettling that the Azure Dynamics motor would exhibit vibration without any major weight attached. I suppose it's possible that the weight of the flywheel could have hurt the motor shaft bearings at these RPMs, though.
Also, keep in mind that the ISR2Hertz RPM gauge on the laptop from the DMOC controller probably had a 0.5 to 1.0 second delay from actual value to read value, so these RPMs may be off.


Here's the final mess after removing the components from the car. I'm not sure where to go from here since the vibrations got progressively lighter as I removed components. I was able to spin the flywheel and AC motor up to 10,500 RPM without getting major vibrations, but these smaller vibrations might be amplified when the clutch assembly and transmission are attached.

My plan is to take the flywheel/clutch to Dan Hall's Automotive Machine shop and have him rebalance it. (He's the only shop in town with a small enough shaft to fit the VW/Porsche flywheels). After that, I hope to put the flywheel back on in several positions on the adapter hub to see if I can cancel out as much of the runout and wobble as possible.

The current runout measurements on the adapter hub are still 4 mils and the wobble is about 1 mil. Perry Harrington, the machinist who created the Electro Auto adapter hub called me last week and suggested getting a brass hammer and tapping the flywheel on moderately tight flywheel bolts to eliminate the runout. I'll keep y'all posted as I get the flywheel back from the balancing shop...

Keeping the Rain Out

Since I live in the Pacific Northwest, I get rather concerned that rain entering the engine compartment will cause problems with the electrical wiring. Many other 914 EV'ers have protected their wiring inside conduit boxes and other shields. I just following the ElectroAuto directions and bolted the relays and terminals blocks to the engine compartment wall with wires dangling from them. This is an idea I came up with to help protect the components.


This is the engine compartment cover removed from the car. I still have the downspouts from the original car, but the original gutter that captured rain from this mesh opening was too large and interfered with the rear battery box.


I drove over to TAP Plastics and purchased a 12"x48" piece of black ABS plastic (for $4.00) to make my own rain gutter. The stuff is remarkably moldable with a heat gun. After making some measurements, I heated up the edges to make a lip for the rain to fall into.


The melting process is basically this: sandwich the plastic between two 2x4s, heat up the protruding plastic with a heat gun and use a third 2x4 piece to bend it down. You need to hold it in place for a few seconds otherwise it tends to bounce back to its original shape.


After melting the bottom and left/right edges, I made a cutout to fit around under the metal pieces to give the plastic shelf a downward slope towards the rear of the car.


Here's a closeup of one end of the finished plastic gutter that goes under the engine compartment hood. I heated up the upper right corner that goes over the downspout and used the end of a screwdriver handle to push the melted plastic into the mouth of a jar to create a depression for the rainwater to flow into. I'll cut a 1/2" hole in the bottom so that the water drains into the downspout. The slot at left (along with the barely noticeable horizontal cut) will fit around the metal struts under the compartment lid.

To hold the bottom edge into place, I'll purchase some short 6mm bolts with large heads to attach the plastic to the original gutter mount holes. My friend wisely pointed out to me that ABS plastic decays quickly in directly sunlight, so I'll probably end up spray painting the surface with an oil-base black paint to prevent the plastic from degrading.