[FTC]: New Fuse Protected Motor Power Cables

Other FIRST Tech Challenge
1

Looks like there is at least one new part already available for the new season:
http://parts.ftcrobots.com/store/detail.aspx?ID=6402

Is this the end of burnt-out Tetrix motors in FTC (& FRC mini-bots)? :wink:

2

Weā€™ve been running those cables on our robot since mid January. Sadly didnā€™t seem to help all that much.

3

Us too. Only thing they were good at was power limiting the motors and going bad at the wrong time.

4

Those arenā€™t really new, they been around for sale since the 2010-11 FTC Season. I donā€™t see any new items around yet. Even the 2011 FTC Resource Kit isnā€™t new IMO.

5

I would love to have more than three gears to choose from. I would also welcome better motors. Then it might not be necessary to worry about burning them up as much.

6

More gears would be welcome, for many reasons.

Most motors will burn up if they are stalled at near full voltage. Itā€™s just how motors work. If not, they need large gear reduction just to get enough power to do anything.

Iā€™d rather have a motor that provides the power that I need, but have to take care with it, rather than one so wimpy that it just sits there when you apply full power.

What we really need are some appropriately sized breakers that can be used to protect the motors when they get mechanically locked. Or, it would be nice to be able to rely on the control system to use the encoders without glitching and running the motors into hard stops at full power :slight_smile:

Phil.

7

I have found that using the encoders to detect if the motor isnt running when it is supposed to be running is a great way to cut off power to prevent the motor from burning out.

In psuedo code:

  • recieve command to run motor
  • wait 30 msec (completely arbritraryā€¦ First number i picked, it didnt shut off too soon, so i ran with it. I plan to experiment and get this number as low as possible)
  • if motor is not turning after this point, shut off power to motor, play error noise on nxt.

This system doesnt work too well with geared systems with a lot of gears where the motor could still be spinning it just would not be spinning the axle needed

Perhaps a shaft encoder would let us detect if both were spinning which would be good. I was contemplating making a shaft encoder but i dont have access to a cnc mill/lathe so it wouldnt be accurate enough to use with the existing encoders. We need these to be provided by LEGO or some third party sensor companyā€¦

8

Youā€™re 100% Correct.

Iā€™ve not tried doing that on a ā€œmove to positionā€, but on our fork lift system last year, we used the encoders to detect when the lift had reached the end of itā€™s travel (and stalled). It would also protect the lift motor if something (eg: a baton) got jammed.

This let us call the raise and lower lift functions with good safety in autonomous and teleop.

When all else fails, Software often comes to the rescue of Hardware :slight_smile:

Phil.

ps: Iā€™m told that the LabVIEW DC Motor Controller interface code is more robust this year, and that many of the glitch modes I reported last year have been mitigated.

It will be interesting to run some tests.

9