7 replies to this topic

[Dave_12]

What is the recommended gearing for a 4500KV motor racing on a King track? 64p. 

[Hot Slots]

The track I race at we use a 4100kv motor, we are restricted to a 11t pinion, I run a 31t spur on .780" tires. It's a Gerding King, so a couple micro blips and your around the track, 3.5 second laps with a GTP body.

I'd throw on a 13t pinion, 33 spur with .750" tires to start, see how hot it gets and go from there.

[Bill Seitz]

David, that depends on whether you want the motor and E-Comm to last through more than one qualifying session and race. The lower the effective gear ratio, the shorter any motor lives, and the faster they start slowing down. Blazing single laps usually result in slow or DNF race finishes.

[Dave_12]

Bill do brushless motors slow down?  I know heat will increase resistance  but what else is there to slow them down? 

[Hot Slots]

Tight gear mesh, excessive track rubbing, etc.

[Bill Seitz]

Heat is the primary enemy in motors, and with brushless, there's also heat in the E-Comm. Heat weakens all magnets, though in most cases they can recover after they cool. Recovery can't occur once the magnet material reaches its Curie temperature, the point where the magnet material permanently ceases being magnetic. With ceramic and cobalt magnets, the Curie temperature is sufficiently high to not be a problem for slot cars. Neo magnets used in brushless and other motors have a much lower Curie temperature - about 200C depending on material - and require a little more care particularly if soldering on the motor. There's some mass in brushed motor magnets that prolong the heating time, but the smaller magnet segments in brushless motors mean heat builds up in them faster. I've unintentionally overheated one of the latest released high performance brushed mini-motors to the point of permanently weakening the neo magnets, so there's definitely a real possibility of this occurring if the motor runs hot.

 

An ESC - electronic speed control - is for radio control. Early slot car brushless experiments used an ESC that had the throttle reprogrammed to be 100% always. Electronics specifically for slot car brushless do not need speed control, since the speed control is via the controller regulating power applied to the lane, so only electronic commutation is required - E-Comm. Throttle and brakes are entirely controlled by the slot car controller. Since the controller cuts power to the car under braking, the brushless electronics turn off under braking and need to power back on and reboot when throttle is restored. Since the E-comm is not running under braking, it has no effect. There are reverse voltage diodes built into the field effect transistors in the E-Comm that allow the reverse current that enables dynamic braking, and control of the braking effect is through the slot car controller.

[aslap]

I'm on a Gerding King at 13.1 V. Using a track DiFalco controller. 1207 5000KV motor geared at 15/37. 0.750 tires with a Westech ESC. Wing car body. Runs 3.0x- 2.9x with one micro-blip coming off the big bank and heading into the turn leading up to the donut. KC Racing chassis. This car was run hard for several minutes and the motor was a tad warm but not uncomfortably so. I've got a 1106 6500KV car ready to go geared at 12/32. It seems to me that on the Gerding King there isn't a whole lot of need for low gear ratio punch. I started off with something like 10/39 gearing and every time I raised the ratio I got faster and the motor was cooler. I also have a 1207 6000KV motored buggy ready but it has been a touch troublesome. I had it geared at 12/33 but with the tiny spur gear, the motor bell was rubbing against the axle. The bigger spur gives me clearance on the bell/axle area. X89 ESC. I'm hoping to get down below the 2.9 number with this one. The track record is 2.2xx with a brushless car. 

 

Tony

[bbr]

I was running 1.8s on Gerding king a couple years ago... this was before all the new escs came out and before the 6 x 9 motors.

With all the new stuff,,, I think you can run in the 1.7s all day