A Schuur thing?

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Just about every big race you attend or hear about, you almost always find a class where the motor is specified as being 17.5 turns. Some people call these classes the “Stock Class” which is ok but most sanctioning bodies prefer to refer them to the number of turns on the motor. Sometimes, old guys like me, do the same thing. So going forward in this review when you see me say “Stock” think 17.5 turn motors and not the 27 turn brushed motors.That brings me to what I will be doing today and that is testing out the SchuurSpeed Extreme SPEC V3 17.5T Brushless Motor.

Everything can be found inside, including a sensor wire.

Everything can be found inside, including a sensor wire.

At the most recent Electric Off-Road Nationals, at SRS Raceway, SchuurSpeed powered two of the three Stock Class Top Qualifiers. Fifty percent of the Buggies and Short Course in the A-main and thirty percent of the Stadium Truck class were powered by SchuurSpeed motors.* While this is only off-road, I can attest to the fact as a tech guy at the IIC, that I did see a lot of the SchurrSpeed motors in use as well. I don’t remember their results because I had other responsibilities at that race but I do know they took home some hardware.

So let’s get to it shall we. Let’s start with the visual observation first. The can itself is well ventilated to allow air to circulate around it to help keep everything cool. The metal sleeve around the stator provides ample room for tech measurement, especially at big events where they measure everything. The solder tabs are very robust, meaning thick and do not bend.

3 screws to disassemble the motor.

3 screws to disassemble the motor.

It only takes three screws to open up the motor for maintenance. Yes you still should do maintenance on brushless motors, especially with the amount and size of vent holes in the can. It just so happens that the three screws take the same size of wrench that you use to adjust the timing. Pay attention to the amount and size of spacers on the rotor as that is a critical piece when you reassemble the motor. You don’t want to lose a spacer because the rotor could come in contact with the sensor board while it is rotating.

There is a non-conductive material underneath the solder tabs to prevent shorts when too much solder is used.The sensor wire plugs in from the side, opposed to the top on other motors, for added protection for the wires. There are timing marks with numbers that you can use for a reference point when reassembling the motor after you clean it. Two screws are used to adjust the timing and three screws are used to hold it all together. The weight of my motor is 170 grams.

Components that make up the Schuur Speed Extreme SPEC V3 17.5T Brushless Motor.

Components that make up the Schuur Speed Extreme SPEC V3 17.5T Brushless Motor.

Now that I have the motor apart let’s look at some of the readings of the motor.

Motor I-Gauss Reading Rotor* Rotor Size* Resistance Reading
Max Difference*
Timing Mark/Measured* Stator Length*
SchuurSpeed Extreme SPEC V3 +1516 / -1505 12.4mm .5 35/40 Avg. 20.0mm

 

*Disclaimer: Each piece of testing equipment that I am using is to be used for reference only just like yours should be used as a reference only. You should never compare numbers between machines because you never know the conditions surrounding my testing and I don’t know yours.

That little black thing at the top is the sensor. Rotors are drill balanced.

That little black thing at the top is the sensor. Rotors are drill balanced.

I have found that when you have a Rotor reading around +/- 1500 it is a good rotor. This rotor is also drilled balanced which is sometimes called dynamic balancing.Just like your car tires are balanced, this balancing allows for a smooth running motor when running. This particular rotor measured at 12.4mm with my caliper. I should probably be using a micrometer to measure the size of the rotor but I found the caliper to be sufficient.

When you look at the size of the hall-effect sensors a slight misplacement can make all of the difference in the timing readings. To the naked eye you won’t be able to tell. That is where the G-Force Timing test comes into the picture. This particular motor had a reading of 39, 40, and 40 for Phase A thru C. That is pretty darn good placement on the board.

Easy access to Stator measurement.

Easy access to Stator measurement.

Now when I look at the stator one nice thing that I mentioned earlier is the ability to measure the stator length without having to take the motor completely apart.This only applies to those races where they will perform this measurement. But you shouldn’t have to worry with this motor not being legal because it is well within the minimum measurement specified by ROAR. This particular stator had a max resistance reading difference between poles of .5 on my MMS. Normally, I would like one to be no more than a difference of .2 but that is just me and it doesn’t mean this motor will be good once everything is working together.

So how does it run? Well, this particular motor does not have the RPM of some of my other motors, but it does have plenty of torque which would allow me to gear up, i.e. bigger pinion. Don’t go overboard on the pinion though because one would probably be sufficient. While we tend to give a lot of credit to the speed control as to how smooth the response is, this motor is more than capable of delivering that power to the track. It brought my bone stock drivetrain in my Kyosho RB6 up to speed without acting like a light switch when exiting corners (on/off) and starting the A-main on the tone was smooth.

Let’s take a look at the high and the low points of this motor shall we?

High Low
Heavy Duty Solder Tabs Resistance reading a little far apart for me (I am picky)
Solid Rotor Strength Measured Electrical timing is ~5 degrees off (seen worse) from can markings
Timing Sensors No external access to bearing by sensor board (Bad for maintenance)
Flat Sensor wire included
Sensor wire comes out the side of the end bell
No external access to bearing by sensor board (No dirt to contaminate it)

 

Overall the SchuurSpeed Extreme SPEC V3 motor, when purchased over the counter that isn’t handpicked, is a competitive motor. Sure for a few dollars more you can get the Signature edition motor and bling it out but if you choose to go with this motor I don’t think you will be disappointed.

*Source: Ron Schuur post on Facebook.

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About Author

I have been involved in R/C since the early 90’s. I have participated in dirt oval, carpet and paved oval, on-road and off-road racing.

I have found ideas that work and ideas that seem to be good on paper but fail for one reason or another.

I have been involved in the rules decision process and tech inspection for one of the largest indoor on-road only events held in the U.S.

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