Motor Tester - Printable Version
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+--- Thread: Motor Tester (/showthread.php?tid=3871)
Motor Tester - JMay - 26th-Aug-23
Motor Tester
The following is a motor tester to find that elusive motor in your collection that has more rpm and torque than the motor next to it in the drawer. This system gives a rpm count at the flywheel by using a sensor and digital RPM display from Ebay/Amazon. By adding a second flywheel which increases the rotating load also gives a broad indication of which motor can sustain rpm better due to its higher torque.
[attachment=31565]
Basis of the system is a magnetic sensor commonly used as an add on to obtain a rpm readout to small internal combustion engines and the like. These are available with or without digital readout from around £5 upwards from various sources. The sensor is built into a 3dp frame to hold the motor and shaft for the flywheel, which in turn holds the magnet to trip the sensor as shown. The motor holder will take any S can (FC130), Boxer or short Boxer and depending on gearing will check up to @40K rpm motors. The sensor and display need a power source 8-12 volts and there needs to be a means of powering and controlling the motor, i.e. using a slot car controller fed from a track power unit.
The 3dp parts are shown below, consisting of a tower, motor holder, flywheel boss, 2 different sizes/mass of flywheels and the sensor disc which holds the magnet. I included some spacers to adjust the motor height above the cog to ensure the correct mesh or to use different diameter cogs, and an adjuster knob which takes a small hex allen driver to quickly tighten/undo the motor clamp allen bolt. Lastly the digital unit has a 3dp receptacle to hold it and can be angled for a better viewing angle.
[attachment=31564]
[attachment=31563]
[attachment=31572]
Purchased parts are
BRM 3mm dia axle
3mm ID flanged ball races
Scalextric 3mm axle SW cog set (other SW cogs will do, need 36T+)
Sloting Plus grub screw pinion 10-12T (rapid & easy changeover)
Fasizi DC 8-24V 4 Digital LED Tachometer RPM Speed Meter with Hall Proximity Switch Sensor NPN 10-9999RPM (Amazon UK)
Additional items
M2 6mm or longer grub screw (Flywheel boss to axle)
Allen bolts M3-M4
Body screw & washers
Wood screws
12v PSU
Slot car controller
Track PSU
Cables
Connecting clips to motor
Volt meter to monitor motor voltage.
Wood, chipboard or MDF block for the tower to be screwed onto
Rubber feet, sponge etc for block to dampen vibrations.
The sensor disc needs to be balanced to offset the magnet weight, and this is done by a small car body screw and washers 180 degrees on the flywheel from the magnet. Balancing can be checked once the sensor flywheel is fitted to the tower axle and ball races, and the wheel spun to find the rest point and then adjusted using small washers. The sensor fits in the tubes in the framework and can be positioned using the lock nuts provided to give the correct gap to the magnet.
Check the sensor and magnet before installation by powering up the sensor, checking the LED changes state when the magnet is presented at the business end. The sensor is polarised to a certain magnet orientation so need to ensure the magnet is assembled into the sensor flywheel with the right face toward the sensor. For the magnet the recess is sized for the Fasizi supplied magnet so may need adjusting for different magnets or for printer tolerance. Lastly glue the magnet in, otherwise as I found during testing at @7000 rpm on the flywheel the magnet detached and was flung across the loft and only found because it was embedded in the loft insulation...
The flywheel boss has a hole to take a M2 6mm grubscrew to secure it to the shaft, the boss has a holes suitable for using a 3mm axle. The flywheels can be left off to establish free running rpm and then added to the sensor flywheel as required to check torque, as the S cans have far less torque the smaller wheel is more suitable and boxers can use the larger one. Note the flywheel boss OD and shaft hole plus the flywheel hole is zero gap so printer dependant this may need to be adjusted to give the required tight but removable fit of boss to axle and flywheel to boss.
When motor testing it is best to back off the brakes on the controller otherwise there is a risk of chewing the flywheel cog if not fully meshed or the clamp is loose. A voltmeter is also handy to check the motor voltage is not sagging under load and affecting rpm.
The above is a simple motor comparative system that can be built for @£40 (depending on what you have to hand) to check rpm and compare torque between motors, to find the best in the drawer.
Cheers
John
Files
[attachment=31566]
[attachment=31567]
[attachment=31570]
[attachment=31569]
[attachment=31568]
[attachment=31571]
RE: Motor Tester - Kevan - 26th-Aug-23
Nice one John.
What is yours printed in?
RE: Motor Tester - JMay - 26th-Aug-23
Kevan,
Printed in Bambu Labs hi flo PLA at 40% fill for the tower etc, the wheels are 60-85% as was aiming at round numbers for each flywheel weight.
Cheers
John
RE: Motor Tester - KensRedZed - 26th-Aug-23
That's a very cool looking motor tester.
Moving the magnet and sensor closer to the rotating shaft would greatly reduce the centrifugal forces at the same RPM... preventing the magnet from taking out an eye.
