Motor Tips |
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Break-in
Each motor is tested before it leaves the factory, but it is a good idea to make sure that the motor is fully broken in before using it under high loads. Just run the motor at 12 Volts for about 10 minutes with no load. Let it cool and do the same in the opposite direction. You might also want to run it a few minutes at 24 Volts with no load.
Repair
You can order replacement brushes here.
Here are some tips if you ever decide to take the A40 or A28 motors apart:
- Remove the brushes and mark them for location and orientation.
- Scribe a line across the rear end-bell and the black magnet housing. When you reassemble the motor use this scribed line to realign the rear end-bell and the housing in exactly the same orientation as it was originally.
- When you reassemble the motor put each brush back into the slot from which it came and make sure to orient them the same as they were originally. If you get new brushes or if you change the orientation of the old ones, you should break the motor in again.
- While you have the motor apart you can check for damage in the brush assembly. Check to see if the spring is still "springy" and the brush slides easily in the slot. You should also make sure that the little felt insulating washers are in place under the brush cap. If you have pressurized air you can blow the carbon dust out of the bush holes. If the brushes don't slide easily you might be able to loosen them up by filing the inside of the brass brush tube. You should take the whole motor apart if you file the tubes.
- Tighten the screws very well. The extreme levels of torque possible with these motors can twist the magnet housing relative to the mounting plate if the screws are not tightened properly.
Timing Adjustment
You can adjust the timing of the A40 and A28 motors by rotating the magnet housing relative to the rear end bell. Your scribed line, (from step two above) will be for neutral timing. Advancing the timing will cause the motor to speed up, retarding the timing will cause it to slow down and run rough. If you plan to use the motor in just one direction you might want to try advancing the timing to get two to three hundred extra RPM. Do not operate the motor with retarded timing. For neutral timing, rotate the magnet housing so that the motor draws the least amount of current. The no-load current should be about 3.5 Amps (A40), 3.4 Amps (A28-150), and 4.5 Amps (A28-400).
Overvolting
We don't recommend running our motors at more than 24V but many people have done it with mostly good results. More voltage is not really a problem for the motors - it's the higher current that causes motor heating, and using higher voltage will cause a motor to try to draw more current. If you are careful about limiting the current or the duty cycle you can get away with higher voltages without damaging the motors. You can limit the current by using a battery that can't supply super-high current, or you can use an AmpFlow current-limiting speed controller, or you can use a torque limiting device like a slip clutch.
For example: The best power to weight ratio for a spinning weapon in a lightweight robot is probably going to be a single A28-150 with a single 36 volt NiCd or NiMh battery pack. At 36V the motor develops 3.2 horsepower at 80 Amps. You probably won't need that much horsepower to keep the blade spinning unless it has very poor aerodynamics or a lot of friction. The battery is six pounds and the motor is 3.8 pounds for a total of less than 10 pounds. The RPM at 36V and 80A will be about 7820 so you need to use an appropriate gear ratio. You probably can't overheat the motor with a single Battery pack, but if you try 36V with two or more packs, you run the risk of overheating the motor. In that case we recommend either torque, current, or duty-cycle limiting. If you don't use any form of current limiting, you should consider using the A28-400 motor instead, (it will handle higher current for longer than the A28-150. For even higher current handling, consider using the A40-300).
Battery Choice
Just as every motor has a maximum horsepower figure, every battery can also be thought of as having a maximum possible "horsepower". Batteries that have very low resistance, can supply nearly all the current the motors can draw. Other batteries have a lower limit to the amount of current they can produce.
Generally, you should choose a battery that has low internal resistance per weight, and use enough of them in parallel to give sufficient run-time. If the resistance is still too high you can reduce the internal resistance of the system even further by adding more batteries in parallel until you achieve performance that is satisfactory. For each configuration, you should check that neither the cost nor the weight go over budget. You should also make sure that the maximum current ratings of the batteries are not exceeded for anything more than brief periods of time.
Technical Specifications
| A40-300 | A28-400 | A28-150 | E-150 | |
| Diameter | 4" | 3" | 3" | 3" |
| Length | 6.9" | 6.7" | 4.0" | 3.8" |
| Peak Horsepower | 3.8 | 4.5 | 3.0 | .5 |
| Peak Torque | 3840 oz-in | 3720 oz-in | 1970 oz-in | 430 oz-in |
| Peak Efficiency | 83.7% | 83% | 81.9% | 74% |
| RPM @ 24 Volts | 4000 | 4900 | 6000 | 4700 |
| Shaft Diameter | 5/8" | 1/2" | 1/2" | 12mm |
| Shaft Length | 1.75" | 1.75" | 1.75" | 1.75" |
| Keyway | 3/16 | 1/8" | 1/8" | 3mm |
| Built-in Capacitors | Yes | Yes | Yes | No |
| Magnet Type | Ferrite | Neodymium | Neodymium | Ferrite |
| No Load Current | 3.5 Amps | 4.5 Amps | 3.4 Amps | 1.2 Amps |
| Terminal Resistance | .050 Ohms | .042 Ohms | .064 Ohms | .375 Ohms |
| Torque Const. (Kt) | 8.05 oz-in/Amp | 6.57 oz-in/Amp | 5.32 oz-in/Amp | 6.77 oz-in/Amp |
| Voltage Const. (Kv) | 168 rpm/Volt | 206 rpm/Volt | 254 rpm/Volt | 196 rpm/Volt |
| Rotor Inertia | .25 oz-in-sec^2 | .05 oz-in-sec^2 | .02 oz-in-sec^2 | .01 oz-in-sec^2 |
| Thermal Resistance | 1.3 degC/Watt | 1.8 degC/Watt | 3.2 degC/Watt | 6 degC/Watt |
| Weight | 11.9 pounds | 6.9 pounds | 3.8 pounds | 3.4 Pounds |
| Cost | $390 | $449 | $344 | $79 |