Drill Motors and HEAT!
 

Posted by Anton Abaya at 2/2/2001 12:00 AM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.



Okay here's the deal...

we were playing with the drills and found out after intensly driving it for like 5 mins, that the left motor gets twice as hot as the right motor.

in other words, the left motor which is the one that goes in reverse is heating up more than the one that goes forward.

Question is: IS THIS NORMAL? i dont know if it's related to the reverse/forward mechanism....i didnt think so. my guess is that the left side is just creating more friction somewhere?

what do you think? thanks..

^anton^

Smells fishy to me...
 

Posted by Joe Johnson at 2/2/2001 4:55 AM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Drill Motors and HEAT!
Posted by Anton Abaya on 2/2/2001 12:00 AM EST:



The differences in the motor from CW to CCW should not
be enough to explain your mixed heating observations.

Friction is the likely culprit.

Have you put the machine up on blocks and tried
backdriving the 2 sides by hand? My guess is that you
will find a very different backdrive effort which will
reflect the variations in efficiency of the two
drivetrains.

Report back the results of the above tests. We will
noodle some more about it if you don't find the
expected results.

Joe J.

Re: Drill Motors and HEAT!REASON.....
 

Posted by nick237 at 2/2/2001 11:10 PM EST


Engineer on team #237, sie h2o bots, from Watertown high school ct and sieman co.


In Reply to: Drill Motors and HEAT!
Posted by Anton Abaya on 2/2/2001 12:00 AM EST:



Anton there is a reason a drill gets hoter in reverse than in forward.
A drill is designed to go forward most of the time so there for the fan that cools the drill is designed to "suck" rather than "blow"
When the motor is ran in reverse for a long period of time the fan is unable to cool faster than when in forward.
The answer is to get a fan that has rotated fan blades.
nick237


: Okay here's the deal...

: we were playing with the drills and found out after intensly driving it for like 5 mins, that the left motor gets twice as hot as the right motor.

: in other words, the left motor which is the one that goes in reverse is heating up more than the one that goes forward.

: Question is: IS THIS NORMAL? i dont know if it's related to the reverse/forward mechanism....i didnt think so. my guess is that the left side is just creating more friction somewhere?

: what do you think? thanks..

: ^anton^

differences in friction still seems more likely...
 

Posted by Joe Johnson at 2/3/2001 4:52 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: Drill Motors and HEAT!REASON.....
Posted by nick237 on 2/2/2001 11:10 PM EST:



It is possible that the fans are more effective in one
direction than another (though I have never seen a
Johnson Electric or Mabuchi spec that mentions this),
but I still think that it is much more likely that
differences in friction between the two drive trains is
the culprit.

I know of a lot of teams that spend a lot of time
worrying about the differences between the Johnson
Electric motor (a.k.a. the Bosch drill motors) when run
clockwise vs. counter clockwise.

In my opinion this is mostly wasted effort. I can tell
you honestly that we have never worried about such
small variations in light of the much larger variations
we expect from the typical drive systems that FIRST
teams make. Many teams spend a lot of time trying to
compensate for this small difference instead of looking
for more important sources of varying output.

But then again, what do I know?

Joe J.

Re: differences in friction still seems more likely...
 

Posted by Brian Cholerton at 2/5/2001 9:56 AM EST


Engineer on team #311, Red Jammers, from East Islip High School and KeySpan Energy, Multiline Corp., Computer Assoc..


In Reply to: differences in friction still seems more likely...
Posted by Joe Johnson on 2/3/2001 4:52 PM EST:



: It is possible that the fans are more effective in one
: direction than another (though I have never seen a
: Johnson Electric or Mabuchi spec that mentions this),
: but I still think that it is much more likely that
: differences in friction between the two drive trains is
: the culprit.

I agree that drive train friction is more than likely the main reason for heat buildup in the motors. Especially when they are used in this application.

One other item that may be adding to the heat buildup in the motor rotating "backward" is the timing of the commutator. DC electric motors are designed to make maximum power, or efficient use of power when rotating in one direction. The cummutator is timed in relation to the magnetic field to achieve this. If the polarity is reversed the motor will still run but will not be as efficient which will result in additional heat buildup.

Just my 2c worth based on a few years of racing slot cars and tinkering with much smaller motors.

Think Backwards
 

Posted by Dodd Stacy at 2/3/2001 9:29 PM EST


Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.


In Reply to: Drill Motors and HEAT!
Posted by Anton Abaya on 2/2/2001 12:00 AM EST:



: Okay here's the deal...

: we were playing with the drills and found out after intensly driving it for like 5 mins, that the left motor gets twice as hot as the right motor.

: in other words, the left motor which is the one that goes in reverse is heating up more than the one that goes forward.

: Question is: IS THIS NORMAL? i dont know if it's related to the reverse/forward mechanism....i didnt think so. my guess is that the left side is just creating more friction somewhere?

: what do you think? thanks..

: ^anton^

Try repeating the intensity and duration of driving you describe, but do it going "backward" in the robot frame of reference. This will invert which of your drill motors is going forward and which backward, in the drill frame of reference.

If the identity of the hot and not-so-hot motors also inverts from your earlier experience, then we can continue the speculation about motor and/or fan directional directional efficiency effects. Otherwise you will know that the driveline is sour on one side of the bot.

It is also possible that the motor itself is sour on the hot side, independent of which direction it spins. Swapping motors (but not gearboxes!) and repeating your original trial (robot going forward) would answer this.

It's called suck and see, Anton. Try it. By the way, you guys who are driving your robots around at this date have my sympathy for your problems!

Dodd