Redundancy of motors

[Brandis]

I was wondering how the redundancy of the motors works. I thought that each motor is connected to one wheel only. So if one motor fails, how can the other take over? Wouldn't you just start to spin because only one wheel is further turned?

Marc

[solotrek]

Hi Marc,
Here's a link for more info.

http://www.segway.com/segway/component_details.html

[Brandis]

Thanks!

My mistake was to think of redundancy between the two motors, but now I understand that EACH motor has 2 separate windings where one can take over the load if the other fails.

Marc

[polo_pro]

Has anyone actually been on a Segway when they're sure a motor winding failed and the system saved them by switching over to the spare winding on the motor? I'm curious how "smooth" the transition is.

ps - As many people have pointed out on this board before, don't go into alot of details if things didn't go well. We'd like not to be the source of bad press.

[bystander]

Originally Posted by plomoh

I'm curious how "smooth" the transition is.

It doesn't switch to the other motor winding and keep going, it switches AND shuts down. Safety shutdown would be initiated as soon as the winding fault was detected. It has to use the other winding to accomplish the shutdown. A user experiencing this symptom would get a red wrench, and the HT probably would not re-start unless the open winding was intermittent.

[Dragan]

Can't say that I have, nor do I know of anyone who's had that unfortunate experience. If I read your question correctly, it implies that the expectation would be that the machine would just transition to single motor operation and continue on it's way.
Not the case; if a motor fails the dual windings will allow the fully functioning system to take the load while bringing you to a controlled stop in a safety shutdown. The redundancy here is not multi-layer..you can't expect safe performance with that much systems degradation, so the best thing for your safety is to stop and shut down
Wayne

[macgeek]

"To protect the human"

If a motor fails, I would hope the rest of the machine would do what it could to save my life.

Thats why there are 'crumple zones' in cars, the heck with the car
... protect the human

Jonathan

[polo_pro]

I was aware that upon winding failure the segway does a safety shutdown. I was trying to avoid saying that term as I delved into this type of problem.

But since my vagueness led to some confusion, I'll be more explicit. When a winding in the motor fails, a segway will go into safety shutdown. This is a very jarring event if you've been travelling at top speed. I was curious if this type of safety shutdown would was more "dramatic" than other safety shutdowns.

Upon losing a winding, I'd think that that motor would momentarily lose some ability to deliver torque to the wheels. Hence as you glide to a stop, would one motor deliver less power causing a turn? Or would their be a sudden jolt (due to less power being delivered to one motor) beyond the usual jolt associated with a safety shutdown?

Maybe I just need to apply my "shorting wire" to the frame and keyport and try out some safety shutdowns on some cushy lawn around here, eh? (Though I'm not sure how I'd cause a motor winding shorting out!)

[Gihgehls]

Originally Posted by plomoh

Upon losing a winding, I'd think that that motor would momentarily lose some ability to deliver torque to the wheels. Hence as you glide to a stop, would one motor deliver less power causing a turn? Or would their be a sudden jolt (due to less power being delivered to one motor) beyond the usual jolt associated with a safety shutdown?

Well, you know..... the control boards in the Segway HT have 3 times the power of a PC, and has for 5 years now! Thats pretty impressive considering how much faster PC's have become in that time. </snark>

But seriously, if they are updating the wheels 1000 time per second, I doubt there will be any noticable difference between a winding-related Saftey Shutdown and any other shutdown.

[bystander]

Regarding loosing a winding,

The following is speculation.

The "other" winding may not be completely idle while the HT is in operation. The controller boards may switch windings at their discretion. Perhaps when one winding is running hot (has higher resistance), the controller switches over to the other one until the temperature evens out.

The precedent is that the batteries are used in an alternative fashion. The controller boards draw power first on one battery, then the other. That way, when one battery gets low, the other can be used for shutdown. Also, when one battery has more "juice" left, it can be used for a higher percentage of the time (say 60/40) until it evens up with the lower one.

In addition, the blinky range indicator always shows the range of the "lower" battery pack. Range estimations are made while using each pack, and the lowest one of the two is sent to blinky.

If the batteries were used in parallel, a shorting fault in one would cripple the other and the safety redundancy would be lost. Therefore power is only being drawn (at any given instant) from only one pack at a time.

Since there are no high power connections between the two controller boards other than the six power wires going to the motors, I would conclude that the way the HT "alternates" using each battery, is in fact, to use the alternate windings of the motors.

Just my observation, it could be incorrect.

I have thought up a way to test the open winding fault. It involves opening the powerbase, adding a relay, and a little soldering. If you're interested, let me know and I'll post it.