Robot Motors- Ampflow Motors Information
Ampflow Motors have been specifically designed
and battle-hardened for use in the BattleBots robot combat competition.
They have also been used in applications like motorized scooters,
electric bicycles, and small electric motorcycles with excellent
results. Take a look at the specifications of the Ampflows.
We think that you will agree that these are the ultimate motors
for combat robots.
We offer three different motors for combat robots:
|3840 oz-in Torque
||3720 oz-in Torque
||1970 oz-in Torque
to go back to the main Ampflow motor page or to purchase
quest for the perfect motor is one that all BattleBots competitors
have gone through. There are several choices available but as many
competitors have found, only a few of them will work well in battle.
What makes a good motor?
There are several things you should consider when choosing
a motor. The most obvious are power, weight, and efficiency, but
there are several other factors that are just as important.
Does the motor have a usable RPM range?
Will it put controller-destroying voltage spikes
on your electrical system?
Is the thing solidly built, or will it fall apart
in the middle of a battle?
Can it withstand the heat build-up of high-Amperage
Will the motor use the limited power you have on-board
efficiently, or will it drain your batteries before the match
Does it produce radio noise and interfere with
your radio control?
Is the motor and shaft designed for easy mounting?
Let's look at each of these questions
in detail and see how the Ampflows handle them.
Horsepower and Torque
Raw horsepower is very important in combat. If you watch
the battles carefully, you will see that the robot with the most
pushing power is often the one that wins. The horsepower and torque
of these motors are higher than other reversible, permanent magnet
motors in this size range. Some gearmotors can't even
achieve 3840 oz-in, and that is after multiplying the torque with
a gearbox. Remember our torque figure is taken directly from the
motor shaft before any gear reduction. (Please note that this is
the theoretical peak torque when stalled. Operating any high-performance
motor while stalled will damage it). Other popular motors put out
1 to 2 horsepower each. With two Ampflows you will have up to
9 horsepower at your command!
Usually, the higher the voltage and RPM of a motor, the
higher its efficiency will be. Some motors have high efficiency,
but at a no-load speed of 20,000 RPM or more. Gearing such high
RPM down to a usable wheel speed takes several stages of gear reduction.
This is heavy and wastes power and the efficiency advantage usually
disappears. The tricky part is making a moderate speed motor that
is also highly efficient. The relatively low RPM of our motors
makes the speed reduction much easier. Most people use one or two
stages of roller chain and sprockets to achieve the speed reduction.
Gearboxes for the A28s are available here.
Solid Construction - Easy Mounting
The Ampflow motors are made from two sturdy aluminum castings and a seamless
body. Some motors use a rolled can with the magnets glued in place.
Motors with rolled construction have been known to rip open under
severe full-throttle direction changes. That can't happen with
our seamless design. The output shafts are 1.75 inches long and
5/8" diameter for the A40 and 1/2" diameter for the A28s.
The long shaft length and a 3/16"
keyway (1/8" for the A28s), make it easy to mount pulleys, sprockets,
and gears in just the position you need them. A second 1/2" diameter
shaft extends 3/4" from the rear of the motors. This is very
handy for mounting encoders, fans, tachometers, brakes, or any other
devices you might need. If you don't need the rear shaft, you can
cut it off flush with the face of the motor.
Some motors use an internal fan to keep
them from overheating. The Ampflows are efficient enough to operate
without a fan. This has three advantages: (1) The motor housing is
completely sealed so nothing can enter the motor and damage it; (2)
The sealed motor tends to contain interference-causing radio frequency
noise that would otherwise escape through the ventilation holes;
(3) The power that would normally be used to run the fan can go directly
to driving your robot.
The armature rides in two large high-quality
ball bearings and it is dynamically balanced using epoxy rather than
by the normal method of drilling the laminations. Drilling can cause
eddy currents in the laminations, which increase motor heating.
Each of the four brushes has its own
heavy-duty motor lead made from mil-spec 10-gauge flexible stranded
wire, (12-gauge for the A28s). Each copper strand is coated with
pure silver to protect against oxidation and to get the lowest possible
resistance in crimped connections. These leads are flexible but not "floppy",
so they tend to stay where you put them. The four leads have high-temperature
Teflon insulation rated for 200ƒ C, (392ƒ F), so they can
handle high current without melting.
Getting high efficiency from a low-Voltage motor is not
easy. There are many factors that will have an effect on efficiency.
We have tweaked each of these factors to achieve the amazing efficiency
of the Ampflows.
|Peak Efficiency (PE)
|RPM at PE
|Horsepower at PE
|Current at PE
|Range of 80%+ Eff.
||.6 to 2.0 HP
||.7 to 2.3 HP
||.6 to 1.4 HP
|Range of 75%+ Eff.
||.4 to 2.6 HP
||.5 to 3.1 HP
||.4 to 2 HP
As you can see from the above chart,
the efficiency of the motors is very high over a broad range of power.
Please note that all our performance numbers are from motors that
have neutral timing. Most motor manufacturers quote efficiency numbers
from motors that have advanced timing. Advanced timing is a bad idea
when you need to run the motor in both directions. Our motors are
shipped with neutral timing for good operation in both directions.
If you use the motor in one direction only, you can advance the timing
and get even more RPM and power. (But do not run the motor backwards
if the timing is advanced). Timing adjustment is easy with the Ampflows.
The armatures are wound with very heavy
gauge wire, and all the space in the armature is used. We left no
power-robbing "empty air" in the slots; they are packed
with copper! The A28s have skewed armature laminations to eliminate
"cogging" that results from using the extremely powerful
neodymium magnets. The A40 motor uses straight laminations, but the
cogging is kept to a very low level by using a 42-bar commutator.
The huge 1.75" diameter of the commutator combined with the
four massive brushes and the 42 bars enabled us to get high power
and high efficiency from this smooth-running motor, (the A28s have
21 bars). As far as we know, the Ampflows have the highest efficiency
of any 24-volt reversible permanent magnet DC brush motors in their
Another benefit of the four-brush, 42
and 21-bar designs is the absence of excessive electrical noise.
While all motors produce some electrical noise, cheaper motors with
fewer commutator bars are more likely to send noisy voltage spikes
back to your controller. This can destroy your expensive electronics.
With more bars, each time a brush comes into contact with a new bar,
the timing of the winding connected to that bar is closer to being
optimal. In low-quality motors with fewer bars, each winding will
pass through a wider range of angular offset from the magnets. This
causes the brush to spark more and generates more electrical noise
and voltage spikes.
BattleBots veterans know how important it is to reduce the radio
frequency noise. Without capacitors most motors will produce enough
RF noise to shorten the range of your radio control. This RF noise
can sometimes make it impossible to control your robot. The Ampflows
come with four capacitors built right in to the motors. Each of
the four brushes has a capacitor wired to its nearest neighbor
on each side. There is no connection to the motor housing. Shunting
your RF noise to the housing, (and ultimately to your robot's frame),
has unpredictable results and we don't recommend it. Mounting the
caps inside the motor works better than mounting them on the outside
but it can be difficult to do. We do the work for you so your motor
is ready to run as soon as you get it!
Efficiency is important for several reasons. A high-performance motor
will convert most of the power it draws into torque and horsepower,
while an ordinary low-efficiency motor will turn much of your battery
power into heat. The weight limits are strict in BattleBots and
it is important to make the best use of every pound of battery
you have on board. Two 12 volt, 16 Amp-hour lead-acid batteries
should have enough capacity to power your dual Ampflow-equipped
robot to victory in a three-minute match. Some other motors require
36, 48, or even more Volts to get sufficient power. More Voltage
means more batteries and more weight. 24 Volts is all you need
with the Ampflows.
Motors that are used in the heavy and
super-heavyweight classes range from about 8 to about 26 pounds.
Motors for the light and middleweight classes range from about 2
to about 8 pounds. The A40 weighs in at 11.9 pounds. The A28-400
tips the scale at 6.9 pounds, and the A28-150 is just 3.8 pounds.
- Just 3.8 Pounds!
Using Your Ampflow motor
The high current these motors are capable of drawing requires the
use of high quality controllers. The terminal resistance of the A40
is .050 Ohms. The A28-400 has a terminal resistance of .042 Ohms,
and the A28-150 has a terminal resistance of .064 Ohms. That gives
theoretical maximum current draws of 375 Amps (A28-150), 480 Amps
(A40), and 570 Amps (A28-400). But in practice, you will
never see this level of current. In order to draw that much
current you would have to use a battery that stays at 24 volts while
supplying high current; you would have to have no resistance between
the motor and the battery; the motor would have to be totally stalled;
and it would have to be at room temperature (the resistance of all
motors increases when hot).
Even the best 12-volt batteries in the
16 Amp-hour size range have an internal resistance of at least .007
Ohms each. Your controller will have at least .002 Ohms. The motors
have between .042 and .064 Ohms. Add to that another .004 Ohms for
your connectors, switches, and wiring, and you will have a circuit
with between .062 and .084 Ohms. This gives theoretical maximum current
draws of 285 Amps (A28-150), 340 Amps (A40), and 390 Amps (A28-400).
The actual figures will be even lower if you have any other load
on the battery (due to battery voltage droop).
This puts the current draw within the
range that some commercial speed controllers can handle. We suggest
that you use controllers from Vantec, IFI, Robot
Solutions, or Robot Power . The motors
have seen action in the BattleBots competition with the Vantec RSFR38E,
RSFR47E, the 4QD-300, and the OSMC and all controllers worked fine.
We have also seen the motor used with two IFI Victors or Thors per
motor (one on each set of motor leads); this has also worked fine.
The motors have also been run with the Vantec RDFR47E and RDFR38E
"dual" controllers that can operate two motors independently.
We don't recommend the dual controllers, but they have worked.
In a recent survey of all the people who used the Ampflows at BattleBots,
there was not a single report of a controller failure!
There are a few ways to reduce the wear
and tear on your controller. One trick is to gear your robot so that
it would be impossible to stall the motors. The more speed reduction
you use, the easier it will be on your motors and controllers. Ten
MPH might not sound very fast, but in the cramped BattleBox it is
very difficult for the larger robots to take advantage of speeds
much in excess of this (unless your primary mode of attack is ramming).
More gear reduction will also give you faster acceleration and maneuverability.
Another trick is to use batteries that
can't produce this high current. If you are worried about your
controller - just don't use those batteries. You should still
get close to the full 4.5 horsepower using most other batteries because,
(like all PMDC motors) the Ampflows produce their maximum power
at 50% of their maximum RPM, and the current draw at that speed is
no more than 240 Amps, (280A for the A28-400, 180A for the A28-150).
Here are some tips for battery selection.
The A40 and A28-400 have tested fine
with momentary current draws of over 500 amps but if you are using
any high-performance motors in your weapon and your weapon becomes
stalled, you must back off on the throttle to prevent damage
to the motors.
By the way, one of the "rules of
thumb" for determining if a motor is high in quality and efficiency
is the difference between the no-load current, and the maximum current.
A good motor might be able to draw 50 times its no-load current when
stalled. Some very inefficient motors can do no better than 10 times
or so. With a no-load currents of of 3.5 Amps (4.5 Amps for
the A28-400), the Ampflows can draw an amazing 110 to 137 times
their no-load currents!
Here are some tips for break-in,
repair, timing adjustments, and technical specifications.
The A28-400 Ampflow
It has long been the tradition in robot combat to use double the
motor manufacturer's recommended maximum voltage. At 24 Volts the
A40 Ampflow is already very powerful. At 36 Volts it will develop
8.6 horsepower, but you run the very real risk of damaging your
motor. If you decide to take the risk, we can offer the following
suggestions: Limit the maximum current to no more than 350 Amps
(lower for the A28s); Use the highest possible gear reduction;
Use the motor in one direction only, do not try to reverse it;
And time the brushes for optimal operation in that direction. The
A28-400 puts out a respectable 1.1+ horsepower at 12 Volts and
over 2.5 horsepower at 18 volts. If you are using this motor in
a light or middleweight and you are bumping up against the weight
limit, you might want to consider eliminating some battery weight
and running the A28s at a lower voltage. More tips on overvolting.
Choosing your motor
Which motor is best for your application? The A28s have
incredible power to weight ratios and for most weight-sensitive
applications these would be the best choice. The A40 weighs more
than the A28s, but in some cases this is advantageous. The higher
motor mass will decrease the rate of motor heating for a given
level of power. If you need high power for several minutes (as
in a continuously spinning weapon), the larger A40 might be a better
choice. The following chart gives some general guidelines for selecting
the best motor.
|Super H.W. Drive
*NCW = Non continuous weapon (hammer, lifter etc.)
These motors are custom manufactured for us by AmpFlow. The motors are warranted to be free from manufacturing
defects, and fully operational when you receive them. The object
of the BattleBots competition is to destroy or immobilize your opponent.
Obviously we can not offer a refund policy for motors that have been
used in these conditions.
Please note that our custom motors are NOT the same as the standard
motors from the Magmotor Company. These motors are not available
directly from Magmotor. Modifications include: High-current brushes
and shunts, brush holders and insulators, high-temperature springs,
custom windings, capacitors, rear end bell, shaft, and oversize
commutator. About the only things the custom and standard motors
have in common are the armature laminations and the front mounting
plate. We do all the customer support for our custom motors. Please
send all questions, billing, shipping, and customer service inquiries directly
to us. (All inquiries to sent to the Magmotor company will
be forwarded back to us).
Price and Shipping
One of our hardest goals was to pack all of these features into a
motor that could be priced reasonably. Using rare earth magnets
is normally the only way to get high efficiency from a low-Voltage
motor. While these magnets are very strong, they are also extremely
expensive. The cost of rare earth magnets in a motor the size of
the A40 would have been astronomical. We studied the alternatives
and decided to go with a high-energy-product ferrite magnet known
as "T9". The T9 magnet material along with the other
design features listed above have enabled us to achieve the same
high efficiency of rare-earth in a much less expensive motor. Our
cost cutting has enabled us to price the A40 at a very reasonable
The A28-400 is smaller than the A40
so we can use neodymium rare earth magnets in that motor and still
keep the price reasonable.
The A28-150 uses less neodymium than
the A28-400 so we are able to price it even lower.
If you calculate the cost per horsepower,
and the horsepower per pound of other available motors, you will
see what great values these are.
a beautiful motor! Wow. Good work. Great price. This should
become standard equipment for all large robots."
--Edwin Wise. Mad
Scientist and author of Applied Robotics
"As the BattleBot
competitions continue to grow, participants are constantly trying
to make their robots quicker, stronger and faster. With nearly
four horsepower and 3840 oz-in torque, the 11.9-pound A40 Ampflow
is ideally designed for our participants. Since power is often
the deciding factor in BattleBot competitions, more and more participants
are selecting Ampflows to power their robots with a lightweight,
high-efficiency motor that provides plenty of power on demand."
Roski. CEO of BattleBots.
"As the first motor
designed specifically for robotic combat, the Ampflow performs
fabulously! It combines incredible power and some of the best features
you could ask for when looking for a high-end motor for a BattleBot.
It is the most powerful and finest constructed DC permanent magnet
motor that I've ever used. I chose Ampflows for the weapon motor
in Nightmare and I am definitely a very satisfied customer!"
--Jim Smentowski. BattleBots
Champion (Nightmare, Backlash)
"The Ampflow packs
a lot of power into a light-weight package. They give Minion the
power it needs and I still have weight to spare!"
Carlberg. BattleBots Champion (Team Cool Robots)
"Get the best motors
you can afford. Good motors are the foundation upon which all else
rests. People can win with hokey electronics or even with inoperative
weapons, but good motors make good robots."
Gurstelle. Author of Building
Bots : Designing and Building Warrior Robots
"We were extremely
pleased with the performance of the 4" Ampflow in our middleweight Heavy
Metal Noise at BB 4.0. The motor supplied an insane amount
of energy to our kinetic disk weapons. Time to spinup was minimal
and after combat the motor was never more than mildly warm to the
--Jay Johnson. BattleBots
Competitor (Big Bang Robotics)
"I've been building
robots as a hobby for about 30 years and this is definitely one
of the best motors (power, weight, cost, quality), that I've ever
encountered. Since I've never built a 'BattleBot' before, I decided
to focus most of my attention on other aspects of the design and
having this motor meant that I didn't have to spend many hours
'tweaking' an inferior motor just be competitive."
Moon. BattleBots Competitor
"I can attest to their
super high quality of craftsmanship and design. We tested them
with a few different controllers and monitored the results using
a Tektronix digital scope and a digital ammeter. Results: This
is the largest motor we have tested and amazingly it had the cleanest
feedback signal of any motor yet. Generally the higher the quality
of motor mechanics, windings, brush and commutator, the cleaner
this signal is. This means these motors are less likely to blow
a speed controller due to transient voltage spikes.
are VERY well built. We saw no appreciable heat up in the testing
we did. We did a lot of stall and near stall testing. These are amazing
motors and are ridiculously powerful."
4/2001. BattleBots Champion (Toro, T-minus, Matador)