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

JDNovak thank you for your post. When I took them apart last time I didn't go far enough and remove the black retaining plate. The locking pins and collar are right there. Tonight we disassembled the window motors and removed the pins. We where able to do this without removing the steering motors from the robot. I did one then the students did the other 3. It is not very difficult. Forget the electrical theories. This is a pure mechanical issue. We ran the robot with the modified steering motors tonight with Jags and have not seen any problems. We are going to an off season competition this weekend and will give it a good test. We took pictures and will create a page on our website to view the evil pins. The problem goes beyond latch up. At low speed and under load the pins cause considerable friction. Other teams noted having hot window motors when driving 2 swerve modules. I bet that with the pins removed their problem would not be as critical. Thanks everyone for your input on this problem. Going forward if this solves the problem FIRST needs to be made aware it. Will pin removal be legal if we get the window motors next year? What is the best notification path for FIRST on this matter.

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

Gdeaver

If it isn't too hard, can you post a couple pictures of the process for those of us who will inevitably end up following your footsteps?

Thanks!

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

Since the GDC (Game Design Committee) has authority to interpret and change the rules, I would think that posting to the official FIRST Q&A forum would be a good way.

Access to the Q&A forum is restricted to one designated person per team. This person has a username and password for access. See this link:

http://usfirst.org/roboticsprograms/...nt.aspx?id=456

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

You might also consider mentioning this on one or more of the official FRC surveys linked here: http://usfirst.org/roboticsprograms/....aspx?id=17127

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

The best thing to start with would be to try to take some pictures, post them here, and explain what's involved. FIRST has been reluctant to allow teams to detach or modify the gearboxes on the window motors (since forever—some of the older window motors weren't so convenient to disassemble, as you probably recall), so it would be great if you could demonstrate that it's no big deal.

Then, we can ask FIRST to have a look (either via the Q&A, frcteams@usfirst.org, or personally to the appropriate GDC members).

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

Gary,
Follow the leads to the Q&A. The GDC has allowed some modifications in the past when it was presented with a benefit to teams to make the modification. Locking pawls in the drill motor transmissions and wires on the Bosch motor are two that jumps to mind.
So did you test with Victors before modifying the motors? That would give us a little more data to actually see if there is some interaction.

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

The steering motors continued to work fine last night. We did not switch to Victors. We took several pictures and put them on a web page. Remember, the window motors were not removed from the robot so the picture quality is not perfect.
Here is the link.
http://wiki.team1640.com/index.php?t...r_Locking_Pins

This is a simple procedure. The window motors allow FIRST to provide a motor and gear box at a economical cost. I think they should continue to be in the KOP as long as First approves the removal of the evil locking pins.

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

Quick update for teams planning on removing their locking pins:
1640 competed at Bridgewater Raritan Battle Royale on Saturday with the locking pins out as above (using black Jags), but still suffered from intermittent steering lock-up. I'm not saying removing them is a bad idea (or a good one for that matter, I have no idea as of yet), but unfortunately it hasn't solved the problem.

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

Nice write up. A few questions.

Does the lock ring have a maximum torque limit? If one continues to add load force does the ring just wedge tighter or will it eventually give?

When the drive shaft engages the locking pin cage, would the command required to move depend strongly upon the direction? This could be estimated by using a JAG step command with increasing amplitudes and seeing what command will break the lock in both directions.

A comment on this diviney statement: When the maximum JAG command authority was applied, I assume it was from a Joystick moved by hand. If so, this would lessen the impulse applied by the motor upon the lock. There just doesn't seem to be any reason that a JAG with a proper waveform input could not duplicate the Victor capabilities unless there is an internal JAG command rate limit that I'm not aware of. With a 100% PWM step input, both the JAG and Victor will reach 10 amps around 2 ms. To reverse and create a matching shutoff like the Victor at .2 duty, the JAG could react within a ms (JAG control iteration rate). It seems plausible that a startup lock breaker pulse could be synthesized for the JAG.

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

The Victor's output PWM frequency is 150Hz. The Jag's output PWM frequency is 15000Hz. The far-lower PWM output frequency of the Victor produces a very "noisy" current waveform in the motor coils compared to the smooth current waveform produced by the Jag's much higher frequency output PWM.

It is possible that the 150Hz "noise" created by the Victor is responsible for preventing the lockup problem. Perhaps 150Hz is close to the resonant frequency of the rotor.

The only way to simulate the Victor's 150Hz output PWM frequency with the Jag would be to create a periodic task running at least 300Hz in the cRIO (to simulate 50% duty cycle at 150Hz). I don't think this is practical.


~

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

Yes..we don't know yet. But it is possible that a single pulse from the JAG that mimics the Victor would suffice to break the static friction and drop the friction to a dynamic value. This is what I wanted the testers to try.

If you held a JAG at 100% pwm for duty/120 sec then the current waveform of the JAG and Victor at the same duty would look identical for a single 120 hz cycle. So whatever the Victor is doing to rattle the lock loose can be duplicated by smart control of the JAG. This JAG breakout waveform could precede any manual command for regular control. Hence a lower duty smooth command to the JAG could then be used in theory since the static lock would be broken.

If that didn't work, then conceivably the JAG command could be Victor shaped continuously. The only limitation is the 1khz JAG command cycle. This is doable as Ether hinted if you insist on using a JAG, but why do it if the Victor works.

By the way, I was able to duplicate the waveforms posted by diviney with my recycled Hbridge waveform simulator that we used in the JAG linearity vs frequency discussion last year. I put in the 2010 Denso , tweaked the i_free to be 1.4 amps (spec 1.8 amps) and upped the motor inductance to 500 uh (was 200uh ) to get a pretty good match of the 20% Victor response. See Fig 4 in Diviney post http://www.chiefdelphi.com/forums/at...1&d=1268192689 and the attached Fig 4. What is unknown is the friction drag...so I assumed that static and dynamic friction currents were equal and added some inertia load.

Using these parameters with the attached denso hbridge vi I ran a 100% JAG pulse for 1/240 sec. ( See attached Fig A. ) and a 50% duty Victor (Fig B). As expected, the current plots match very close. So, if a single pulse Victor can shake it off the lock... then why not the JAG?

PS. Sorry the figure titles aren't showing... just mouse over them to get titles

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

Chris,
Interesting premise... The only difference would seem to be the refresh pulse for the bootstrap cap in Jaguar. The manual does not list the refresh rate for the charge circuitry. Only this...

"This state only occurs when the motor is running full-forward or full-reverse. The MDL-BDC software intermittently switches to the low-side MOSFETs for a short duration to replenish the bootstrap capacitor. The short duration has no impact on motor speed."

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

This thread has grown cold but, I'm reviving it one more time to update our summer experience. As mentioned, we did have random and intermittent wheel lock up at a off season competition with the locking pins removed. The Denso motors run much cooler with out locking pins. We replaced the jags with Victors before IRI. Since we went to the Victors we have not had a Denso motor problem. The only guess to the problem with Jags and window motors is that the high switching frequency and the motor PTC cause a self heating of the PTC. After this experience I would strongly suggest that any team that uses window motors should only use Victors. We did not test with locking pins in and Victors but, the performance with out locking pins is much better.

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

We had a similar experience with a black Jaguar driving a flywheel.
The Jag couldn't handle full current after it heated up a little without faulting.

The problem could be avoided by ramping up slowly, but it wasn't a sure thing. Swapped in a Victor and the issue went away, if a tiny bit noisier as it maintained a set tach reading. The Victor didn't show any stress via excess heat.

I suppose the lesson is to test the Jaguar rigorously in the application ahead of competition if possible.

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

What kind of motor was the Jag driving ?