10th-Sep-20, 06:12 AM
You have slot car and you race competitively.
You have a selection of motors and you'd like to test them.
I have never found a motor that meets the published specifications.
All motors vary one way or the other, from new, and also change with use.
1. Power supply
I have a fusion PSU as shown in the link below
2. Tachometer
You can either buy a laser tachometer like the one below
Or use a Mobile app such as GiRi. See pic
Take an old wheel or crown wheel and place a fluorescent tab on it.
https://ibb.co/2KDytJS
3. Torque arm
Static torque : A 10cm arm can be made of a kebab stick and an old ripped up crown wheel
Dynamic torque measurement requires tools I've not seen in the slot car market.
https://ibb.co/nss58CR
4. Weigh scales
Decide on a voltage.
Manufacturers often state rpm (speed) and G/Cm (torque ) numbers but often fail to state the voltage that these specs are meant to reflect. Some manufacturers quote numbers for 12v , others higher. Some omit the voltage numbers altogether.
Whatever you decide ( I suggest 12v) test all of your motors at the same voltage.
‐-------------------------
There are two factors to consider when measuring motor performance
A. Speed
Revs per minute at fixed voltage
A motor that does not rev at a sufficient RPM will not be very quick.
B. Torque
How hard does the motor pull at a fixed voltage?
If the torque is low , the motor may not be able to pull the skin off a rice pudding, the acceleration will be poor and it is likely that the braking will also be poor.
------------------------------
Testing motor SPEED
Power up the motor and take a reading with the Tachometer.
Job done? Not quite.
Motors often run at different speeds clockwise and anti clockwise.
It is always good to know if a motor has any bias that might be leveraged by installing it in a car where that bias is beneficial, not detrimental.
This bias occurs because of a build quality control issue. The commutator is not perfectly aligned with the armature stack.
Testing motor TORQUE
A simple way to test torque is a "stall-test".
However, stalling a motor at 12v is risky. High current draw can burn the motor.
Thankfully, torque is linear , so test at 4v and multiply the result by three. Easy.
Take the readings at various points in the motor's cycle.
Motors do not produce the same torque at all points in their cycle so take many readings and record the best result you see.
If you take an average you may find your reading are much lower than the mfr. Spec.
I use a 10cm torque arm , so, if a motor is pushing 10 grams on the scale at 4v.
10g x 3 x 10 = 300 G/Cm (the calculated torque reading at 12v)
How to make the best of your readings:
Always try to install a motor so that it runs in the direction in which it runs fastest.
Motors that are clockwise biased are better suited to left hand drive sidewinder&anglewinder or inline installations with the crown wheel teeth on the right ( as viewed from the rear of the car)
Motors that are anti-clockwise biased are better suited to right hand drive sidewinder&anglewinder or inline installations with the crown wheel teeth on the left. (Viewed from the rear, above the car)
Always take a record of your motor testing readings.
The records allow you to monitor the performance of a motor as it ages.
It's good practice to test and record each time a motor comes out of its motor pod.
I have found that motors improve with age but their best performance appears to be just prior to the performance "falling off the cliff".
Be aware that manufacturers often design their cars with no way to install the motor in the direction in which it runs best, even if fitted as an inline installation.
NSR inline crowns can support left and right drive inline crowns but the crown size is more limited by the chassis design on the triangular "evo" pods.
Slot.IT inline offset crowns are designed to be installed in one direction only.
You may have to take your motor and run it in another manufacturer's car to get the most from it.
Don't get tripped up by the installation orientation. Some designs fit pinions at the can end, others at the commutator end.
(Clockwise at the can end is anti clockwise at the comm end and vice versa)
Don't assume that manufacturers optimise their motors to run in the direction that suits their cars.
Eg, most of my NSR motors that show a bias, run fastest clockwise.
Get on top of the information above and implement it.
It won't take long before other racers are aiming that slotters lament at you " Wot've you got in that??"
AlanW
Do you have alternative testing methods?
You have a selection of motors and you'd like to test them.
I have never found a motor that meets the published specifications.
All motors vary one way or the other, from new, and also change with use.
1. Power supply
I have a fusion PSU as shown in the link below
2. Tachometer
You can either buy a laser tachometer like the one below
Or use a Mobile app such as GiRi. See pic
Take an old wheel or crown wheel and place a fluorescent tab on it.
https://ibb.co/2KDytJS
3. Torque arm
Static torque : A 10cm arm can be made of a kebab stick and an old ripped up crown wheel
Dynamic torque measurement requires tools I've not seen in the slot car market.
https://ibb.co/nss58CR
4. Weigh scales
Decide on a voltage.
Manufacturers often state rpm (speed) and G/Cm (torque ) numbers but often fail to state the voltage that these specs are meant to reflect. Some manufacturers quote numbers for 12v , others higher. Some omit the voltage numbers altogether.
Whatever you decide ( I suggest 12v) test all of your motors at the same voltage.
‐-------------------------
There are two factors to consider when measuring motor performance
A. Speed
Revs per minute at fixed voltage
A motor that does not rev at a sufficient RPM will not be very quick.
B. Torque
How hard does the motor pull at a fixed voltage?
If the torque is low , the motor may not be able to pull the skin off a rice pudding, the acceleration will be poor and it is likely that the braking will also be poor.
------------------------------
Testing motor SPEED
Power up the motor and take a reading with the Tachometer.
Job done? Not quite.
Motors often run at different speeds clockwise and anti clockwise.
It is always good to know if a motor has any bias that might be leveraged by installing it in a car where that bias is beneficial, not detrimental.
This bias occurs because of a build quality control issue. The commutator is not perfectly aligned with the armature stack.
Testing motor TORQUE
A simple way to test torque is a "stall-test".
However, stalling a motor at 12v is risky. High current draw can burn the motor.
Thankfully, torque is linear , so test at 4v and multiply the result by three. Easy.
Take the readings at various points in the motor's cycle.
Motors do not produce the same torque at all points in their cycle so take many readings and record the best result you see.
If you take an average you may find your reading are much lower than the mfr. Spec.
I use a 10cm torque arm , so, if a motor is pushing 10 grams on the scale at 4v.
10g x 3 x 10 = 300 G/Cm (the calculated torque reading at 12v)
How to make the best of your readings:
Always try to install a motor so that it runs in the direction in which it runs fastest.
Motors that are clockwise biased are better suited to left hand drive sidewinder&anglewinder or inline installations with the crown wheel teeth on the right ( as viewed from the rear of the car)
Motors that are anti-clockwise biased are better suited to right hand drive sidewinder&anglewinder or inline installations with the crown wheel teeth on the left. (Viewed from the rear, above the car)
Always take a record of your motor testing readings.
The records allow you to monitor the performance of a motor as it ages.
It's good practice to test and record each time a motor comes out of its motor pod.
I have found that motors improve with age but their best performance appears to be just prior to the performance "falling off the cliff".
Be aware that manufacturers often design their cars with no way to install the motor in the direction in which it runs best, even if fitted as an inline installation.
NSR inline crowns can support left and right drive inline crowns but the crown size is more limited by the chassis design on the triangular "evo" pods.
Slot.IT inline offset crowns are designed to be installed in one direction only.
You may have to take your motor and run it in another manufacturer's car to get the most from it.
Don't get tripped up by the installation orientation. Some designs fit pinions at the can end, others at the commutator end.
(Clockwise at the can end is anti clockwise at the comm end and vice versa)
Don't assume that manufacturers optimise their motors to run in the direction that suits their cars.
Eg, most of my NSR motors that show a bias, run fastest clockwise.
Get on top of the information above and implement it.
It won't take long before other racers are aiming that slotters lament at you " Wot've you got in that??"
AlanW
Do you have alternative testing methods?
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