Excuse II
Four
ML-30 12 Volt 30:1 motors were ordered from
The Robot Marketplace.
Excuse was completely disassembled. The original .060" carbon
fiber laminate chassis was reinforced with a second piece of .060"
carbon fiber laminate. A new fixture was made to hold the motors
in align while they were epoxied together. The original optical
mouse was removed and it's hole filled in. New mounting points for
the motors were drilled and everything was mounted. A set of Kokam 1050
ma-hr batteries was ordered for the larger motors.Once running, the speed of Excuse was less than before at 31.6 inches per second on twelve batteries. Even though the speed was down, acceleration was noticeably improved. The simple solution to increasing speed is to add batteries, but the H bridges were limited to 20 Volts maximum. Any more than twelve batteries would harm the MOSFETs in the bridge.
The
bridge circuit was redesigned to allow higher voltages. The additional
resistors, Zener diodes, and Schottky diodes did not add substantially to the size of
the control board. The
schematic on the left is one H bridge. Two are required for the
total installation. The optical mouse PAK was removed. No
other changes were made in the control.
The
original Pololu driver schematic is also printed here. Notice that
there are several "pull down" resistors added to assure that the MOSFETs
do not inadvertently turn on. One of these Pololu controls will
drive both of the H bridges. Also, since the voltage is
increasing, a switching voltage regulator was used to replace the
original LM2940. Both Excuse and Sticky have experienced occasional
resets due to the LM2940 thermal shutdown.
The
sensor package remains the same. Here is the schematic for both
the bumper mounted electronics and the control board mounted
electronics. The adjustable voltage regulator has proven to be
extremely handy for adjusting to local lighting conditions and other targets
outside of the Sumo rings (judge's legs and things).
With the new, higher voltage H bridges and sixteen batteries, Excuse now has a speed of 43.2 inches per second. This is acceptable. Also, from test results, it appears that Excuse reaches full speed in much less than one inch. On the Exert-O'Meter, the 4.1 pound Excuse pushed 15 pounds and was very stable. That is 3.66 times the weight of the robot...a new record. While pushing at 15 pounds, the total current draw from the batteries was just 5 amperes. This compares to 10 amps for a heavier, slower Sticky pushing the same amount.
Videos of the Summer, 2004 NEIRG competition:
2A Excuse vs Mad Dog (0:11 - 0.5Mb) 2B Excuse vs Mad Dog (0:27 - 1.2Mb)
10A Excuse vs Shunji (0:11 - 0.5Mb) 10B Excuse vs Shunji (0:07 - 0.4Mb)
14A Excuse vs Shunji (0:07 - 0.4Mb) 14B Excuse vs Shunji (0:08 - 0.4Mb)
At
the Summer, 2004 NEIRG, it was clear that a "kill" switch would be very
handy due to the speed of Excuse. A remote switch identical to
Flaming P'nut was added, but electrical noise from the motors made the
switch very unreliable. The normal method to control electrical noise is
with small capacitors from the motor wires to the motor case.
There was not sufficient room to add the capacitors, so the motors were
cut apart and the capacitors were added. Since the motors were
apart, the rear "suspension" was modified for two reasons. First,
more clearance was needed so that the rear of the chassis did not drag on the ground
(lifting the rear tires) when Excuse would climb onto an opponent's scoop. Second, in an
attempt to control the jumping around of the rear wheels, the mass of
the batteries were added directly to the rear motors. Since there
was more room,
seventeen batteries are glued to the redesigned motor mount.
The
capacitors did not help the kill switch operation. A new
transmitter module was available for the kill switch which was
advertised as increasing the range to 1 Km. The transmitter module
was installed and worked flawlessly. No receiving antenna is
needed on Excuse.The seventeen batteries increased the speed to 45.7 inches per second and increased the weight to 4 lbs. 3.8 oz. An Exert-O'Meter test produced 11 lbs. of push and still much jumping around. This was a big disappointment! That is four pounds less push. It is possible that the higher tire speed is affecting push. The motors were run at full speed, then the speed was slowly reduced. Push remained constant down to 70% of full speed, then slowly dropped. At 37% of full speed the push was still 77% of maximum. So it doesn't appear that the higher speed is a detriment to push.
Excuse won the Heavyweight Autonomous Sumo class at the 2004 CIRC Competition.
Videos of the Peoria Competition:
4A Excuse vs Dozer (0:08 - 0.4Mb) 4B Excuse vs Dozer (0:07 - 0.3Mb)
5A Excuse vs Brutus (0:07 - 0.3Mb) 5B Excuse vs Brutus (0:09 - 0.4Mb)
8A Excuse vs Brutus (0:15 - 0.7Mb) 8B Excuse vs Brutus (0:07 - 0.4Mb)
Two
changes were made for Excuse in preparation for the 2005 NEIRG.
First, in the constant quest for more speed, six more cells were added
to the battery pack to make a total of 23 cells. Second, a lead
weight was added directly over the rear motors to reduce the rear wheel
bounce when pushing hard.
The
higher voltage (31 to 32 volts) was over the rated limit on the Power
Trends voltage regulator that was used, so a new 5 volt switching
regulator from Datel (7805SR) was used. Datel recently combined
with
C&D Technologies and the
7805SR is available on their web site.
The twenty three cell battery increased the speed to 53.3 inches per second and increased the weight to 4 lbs. 10 oz. The speed was a little disappointing since I was expecting something over 60 inches per second. There was way too much rear wheel bounce to measure push, so the hunk of lead was added to try to settle down the bouncing. The lead brought the total weight up to 2.9 KG for the heavy weight class. A Final Exert-O'Meter test produced 12 lbs. of push and the extra weight only slowed the frequency of the bounce.
Excuse did not win the Heavyweight Autonomous Sumo class at the 2005 NEIRG Competition. After an easy match against Dozer (the eventual second place winner), Excuse went up against the ultimate winner, Titan.
Watch the Video: 5A Excuse vs Titan (0:26 - 0.5Mb)
As
you may have noticed, Excuse stopped pushing and was eased out of the
ring by Titan. Excuse's two left side motors stopped running.
After the event the motors were disassembled and all of the solder was
melted off of the armature and sprayed onto the motors magnets.
Without the solder, the armature wires just slipped off the terminals
and the motors stopped. I guess that twenty three cells may be a
little much for the 12 volt motors.
The motors have been replaced, the battery pack is back to seventeen cells, and the lead weight has been removed. Excuse is now a test mule for future experiments.