Denso Window Motors, Warning - Don't use with Jaguars !

[Ether]

Since it's been a while since there has been any activity on this thread, and there were over 70 posts, I took the liberty of excerpting some of the observations and problem descriptions that have been posted. The number before the right paren is the post number.

Considering DavidGitz's post#55, it would be most interesting to get an answer to EricVanWyck's question in post#74

Also, has anyone experienced this problem with BLACK Jags and window motors? See post#4.

1) diviney

...Denso window motors that came in this years KOP. ...This motor used a Jaguar controller...

...the motor will occasionally simply fail to respond to the controls. When the motor fails to respond, there is a voltage present on the input to the motor. We could hear a high-pitched sound from the motor as further indication that it was being powered.

There was no mechanical interference, yet we found that there was sort of a mechanical hysteresis taking place. If the arm was commanded to go down, but was unresponsive, we could gently push it up with our finger and that would cause it to properly drive down in response to the command. Likewise, if the arm was commanded to go up, but became unresponsive, we could nudge it down and it would respond by driving up as commanded.

We tried a spare motor, but if anything it was worse with the replacement motor.

This is not a fluke due to a bad Jaguar or a bad motor because we saw it with 2 different motors and 2 different Jaguars.

we substituted a Victor speed controller, and everything then worked perfectly.

One final observation - we were not able to get the motor to fail by simply commanding it on and off. By using the joystick to vary the speed up and down, forward and backward, it would fail readily. If you are not varying the speed and just want forward / reverse on / off, you [might] be OK.

Both of the Jaguars we tried are the older brown ones. We have not tried this on one of the newer black ones.

4) big1boom

We are running 3 Denso's off of 3 Black Jaguars on CAN, and have had absolutely no problems with them.

5) Mr.G

We are using all victors this year... The problem occurs for us when the motor gets hot.

9) diviney

switching to a Victor has completely eliminated the problem.

54) Kingofl337

We have noticed the stalling issue which causes the motor to stop moving but keep overheating.

Our fix was to monitor the wheel and disable the PID control for 1 second if it stalled. Once the PID is re-enabled the motor behaves normally

55) DavidGitz

sometimes when the robot is rebooted (after allowing a lot of time to cool down, i.e. the motor is cool to the touch) the window motor will not move anyways. If we disable and re-enable it will come back and start working.

61) billbo911

We know the Victors work well with the window motors and have for years.

The window motors work well with the Spike relays.

66) diviney

The Denso motor fails to start reliably even when 100% drive is applied (and the PTC is not tripped). The voltage waveform is correct, and the current is high. It just acts like it's stalled even though there is no mechannical load. We can easily get this to happen with just the motor (nothing connected to the output shaft).

The motor does not start even if you try to "help" it move in the commanded direction.

When the motor is "stuck" like this, you can coerce it to start by turning it in the OPPOSITE direction. A slight nudge in the opposite direction makes it suddenly free up and turn in the commanded direction. It is as though there is some sort of backlash in the worm gear, and shifting this backlash causes a release of tension, freeing the motor to turn in the opposite direction.

We can NOT get the motor to fail in this way with a Victor powering it. There was some mild evidence of sticking, but it always freed up with a command authority much less than maximum (maybe 25%) wheras the Jag could not start even with maximum command authority, happily drawing > 10 amps (until the PTC tripped after many seconds).

With the Victor, the motor growls as it begins to start. With the Jag, it's a high pitched squeal. Could it be that the growling vibrates the worm gear enabling it to move the backlash just enough to start when the high-frequency of the Jag cannot?

[Gdeaver]

When this happens we are running competition code and can not set the PWM to 0. We can switch directions and this has no effect. In the beginning of the season, I pulled the pwm cable and reinserted. This should have caused a time out and set to zero. Put the cable back in and nothing. Power cycle solves problem. Have not tried pulling breaker. We can go many matches and not have it happen. Happened to a replaced window motor. Seems to happen with any window motor. This is very irritating because now now that we have the swerve dialed in the robots great except for this last issue. We are using tan jags. Because there is PID involved switching to victors is not the best solution but it's the only thing we know to try. Any other ideas?

[Ether]

Originally Posted by Gdeaver

We are using tan jags.

Because there is PID involved switching to victors is not the best solution but it's the only thing we know to try.

Any other ideas?

Do you have a black Jag you could try? See post#4 in this thread.


~

[Al Skierkiewicz]

Gary,
I had received no further reports of issues with Window motors. However, I reviewed the waveforms Tom posted on the previous page. If his captured waveforms are correctly identified, there would seem to be a typical inductance current waveform on the Victor pictures at less than full throttle while the Jaguar waveforms show no sign of inductive current which they should at 15kHz. Since there is no reactive component to the Jaguar waveforms, is it possible that the temperature protection has some fairly high impedance at 15 kHz?

[Gdeaver]

We changed the tan jags to black jags with coast last night and it still happens. If I catch it as soon as the motor locks and pull the PWM cable and reinsert the motor functions. With the black jags once a motor locks it heats up faster with the black jags. < than a minute till the PTC resistance goes high. It heated slower with tan jags. We will install victors Wednesday night and see if victors are the answer. I took apart a spare window motor and there are 2 chokes and 2 caps in addition to the PTC. We could short the PTC now that it is off season but will do the victors to test. If the victors work then there has to be some weird resonance setting up between the filters, PTC and the jags frequency causing the PTC to heat. If the victors work then the jags will always be suspect with emi filtered and PTC protected motors. Maybe this is one reason IFI never went above 2000 HZ switching frequency.

[Jester Jackster]

all we had was a winch connected to a regular andymark gear box.

[Al Skierkiewicz]

Gary,
The chokes and caps are for brush noise RFI suppression and should not pose and significant impedance at 15kHz. The core of the chokes would need to be really big to be effective at that low a frequency. Is there any markings on the PTC?

[Ether]

Originally Posted by Gdeaver

We changed the tan jags to black jags with coast last night and it still happens. If I catch it as soon as the motor locks and pull the PWM cable and reinsert the motor functions. With the black jags once a motor locks it heats up faster with the black jags. < than a minute till the PTC resistance goes high. It heated slower with tan jags. We will install victors Wednesday night and see if victors are the answer. I took apart a spare window motor and there are 2 chokes and 2 caps in addition to the PTC. We could short the PTC now that it is off season but will do the victors to test. If the victors work then there has to be some weird resonance setting up between the filters, PTC and the jags frequency causing the PTC to heat. If the victors work then the jags will always be suspect with emi filtered and PTC protected motors. Maybe this is one reason IFI never went above 2000 HZ switching frequency.

Great post Gary. Thanks for the data. This really helps narrow down the problem... assuming everything works fine when you use the Victors.

Al: I know you have lots of documents. Do you by any chance happen to have a circuit diagram of the chokes and caps in the Denso? I'd like to see how they are arranged.

[JDNovak]

The first problem you are dealing with is a mechanical one. The window motor interface to the gearbox pinion has an anti-backdrive mechanism that locks the shaft. if there is intermittent back pressure on the gearbox output shaft it locks easier. This was probably to keep someone from prying the window down because the worm gear pitch isn't steep enough to negate backdrive.

If you are driving a load and the load doesn't keep up with the motor, it sets the mechanism and locks. if nothing detects the lockup and stops the output within a few seconds the motor protection takes over and you're done until it cools down. If you remove the output soon enough and then drive in the same direction again, the mechanism will unlock assuming the load will move. Driving in the opposite direction does not unlock the mechanism unless the load relieves on it's own.

I believe the theory that the motor shaft vibration caused by the Victors at 120hz aids in unlocking the mechanism while the Jaguars smoother output doesn't.

Just some of the frustrations of mating devices and technologies that were never designed to go together but enabling kids to keep after it until something works will hopefully pay off down the road of developing the next generation of stuff.

To test these theories, you might try driving the system into a load that is controllable (like pushing back and pulling on the steered module) and see what happens.

[Ether]

Originally Posted by JDNovak

The window motor interface to the gearbox pinion has an anti-backdrive mechanism that locks the shaft.

John,

Is it fairly simple, and non-destructive, to separate the motor and gearbox in order to see this?

If not, did you guys take any pictures you could post ?

Thanks.

~

[JDNovak]

Just remove the phillips head screws that hold the motor on.
The motor shaft will have a three-lobe coupling on it that interfaces with the gearbox. I believe the gearbox side is metal. There is a brown plastic ring around the metal that contains locking pins. When the brown ring and metal coupling are misaligned they lock. as long as the pieces are rotating together they turn freely. I think the rings are retained by a thin metal plate.

I'm reciting this from memory as I haven't looked in one for three months so there may be inaccuracies but I think if you play with it you will see how it works. Turning the output shaft locks the coupling. turning the coupling with the motor drives the locking ring with it to keep it from locking.

[Al Skierkiewicz]

I have not found any schematics in my files. Typically, chokes are wired in series with each brush and capacitors are wired across each electrical input wire with the other end tied to the motor case. In this configuration (looking from the brushes) the two components form an L/C low pass filter that filters out RFI before it leaves the motor.

[Jon236]

Thanks to everyone on this thread who has contributed to the body of knowledge here on CD!

I know there are a number of white papers and PPP available on motor selection, examining power curves, etc.

Has anyone posted a comparative table evaluating the KOP motors in a qualitative sense? In other words, 1-5 stars for use in various applications, such as drive, winch, steering, etc? I know it would change from year to year and need updating, but a general guide would be useful to rookie (and some veteran) teams to start the selection process.

We need to have the students more involved in these decisions, and lifting the veil of mystery would be helpful.

This doesn't stop them from doing the actual calculations to see if they can lift 3 robots with a window motor!!

[EricVanWyk]

Ether - Thanks for compiling all those. It sparked a thought.

Theory:
Some Denso motors brushes are failing in such a way that too many windings can be active at the same time. This may be due to a winding-winding short, a brush deformation, or simple poor design. This state is limited to a limited portion of the rotary travel.

Direct Result:
While in this state, several things occur:
* Current increases: More windings means more mhos.
* Torque constant greatly decreases: Windings fight, reducing effectiveness. Imagine a shaft with a keyway in it: This is the extremely over simplified diagram of the torque constant vs angle that I'm imagining.*

Matching Symptoms:
* The motor will tend to lock into the keyway, given a load that is between the depth of the bore and the outer radius.
* Applying extra torque can pop it out.
* If the bore is deep enough (and it could be very deep), "smooth" current won't do anything.
* "Rough" current has the advantage of being little bursts of torque. This has the possibility of pushing a little harder momentarily (duty cycle <100). It also has the advantage of giving up, letting it roll the wrong way (out of the bore) and then charging forward over the valley.


Does this match up with other folks thoughts?

* Sorry for the weird bore analogy. Better wording of it would be appreciated.

[Gdeaver]

We removed a window motor in the beginning of the season. I disassembled and inspected the motor. there was no visible wear or signs of a mechanical problem. That was before we realized that all window motors were having very random and intermittent lock ups. We can go for hours of practice and not have a lock up. The randomness makes this hard to track down. When I took the window motor apart on Monday night, I did not see any locking pins. I thought that that was just a flexible shaft coupler. Tonight we will install victors and test a new autonomous mode. We are also going to a competition this weekend and should get more data. One thing I noticed and do not want to state as fact is that when the lock happens the jag stayed solid red even when an opposite direction input was applied. I want to consult others before this is stated as true. If so this is a really weird one. If we can resolve this then we can consider the 1st season 4 wheel independent steering and drive swerve system a success.