[Dr_C2]

On the ‘old’ forum there was lots of discussion and early trials of brushless motors in slotcars including in digital slotcars.

Drifter2 has more recently carried out some interesting trials with sensored brushless motors which look impressive and highly positive as a future race option. Link below:

https://slotracer.online/community/showt...p?tid=4217

As my high speed ‘drag strip’ instrumented test track is upgraded with a large digital speed read-out display - it’s become a useful test environment for my own experimentations with sensored brushless motors.

Having used brushless motors in model aircraft for many years - their use in digital slotcars is hardly fundamental research - it’s more about optimisation as a route to assessing ‘usefulness’ as compared with the brushed motors. The latter are of course the current norm across the slotcar hobby.

Like Drifter2, I believe ‘sensored’ motors are the best starting point for brushless slotcars in order to achieve smoother low speed running. These motors have internal Hall sensors to report rotation phase. Simpler non sensored brushless motors rely on back-EMF to measure rotation phase which works best at moderate and high speeds, but poorly at low speeds.

My experimentations will use digital control only as others are busy developing and in some cases selling brushless motors for analog systems.

My plan is three stage and likely to run through 2025.

Stage 1: use commercial sensored brushless  motor and electronic speed controller (ESC) in conjunction with Spektrum DSMR r/c system. This approach will pick up DC power from rails and then step down to 7.5V using a buck converter.

Stage 2: Use commercial sensored brushless motor and ESC in conjunction with an SSD decoder which has a modified output to match the input ‘servo’ pulse requirement of the commercial ESC. In this case track power will be SSD digital and a combination of bridge rectifier plus buck converter will be used to generate 7.5V DC.

Stage 3: Here the commercial ESC will be replaced with a Texas Instruments IC to provide a small footprint in-car solution. The ICs of particular interest are the DRV10970 and the newer variant, the MCT8316Z.

In my previous experiments a few years back I used sensorless brushless motors and a simple controller which could be driven by a standard digital decoder motor PWM signal. It drove but had no brakes. At that time I used a slot.it motor pod and a PCR chassis.

This time around the mechanical platform uses the NSR Z4 chassis with side-winder, angle-winder and in-line motor pod configuration options.

I hope this new thread will be of interest both to hobbyists and system developers.

Current status: the brushless motors and ESCs have arrived and the Z4 chassis are patiently waiting for they drive system install.

Apologies this post is rather long but I did want to frame correctly the upcoming project effort. Future posts on this thread will be shorter and to the point!

Meanwhile, thanks for reading - and as always, all comments and thoughts are welcome.

c

[Kevan]

Sensored brushless motors are so much smoother than sensorless in a car, it was like chalk and cheese when they first came out for RC cars many years ago.

[Dr_C2]

Many thanks Kevan.

And, the motor/ESC combinations I have on the bench are already proven for 1/28 scale r/c cars so we should be off to a strong start :)

c

[Dr_C2]

Starting with the end in mind, if the Texas Instruments ICs I mentioned are to be used, then there needs to be a method to enable adjustable braking too.

From the datasheets these ICs have a digital input to select what happens when the throttle command is set to zero. The options are electronic braking or coasting.

So the key question here is can the digital input be driven by a PWM signal to enable adjustable braking?

So far the datasheets are unclear on this point - so let’s turn to the test bench to find the answer.

c

[Dr_C2]

I’m planning to use two variants of in-runner sensored brushless motors:

4300kV 1625 (16mm x 25mm) motor

and

5500kV 1525 (15mm x 25mm) motor

both variants have a 2mm shaft and the motors should fit nicely into NSR motor pods. Photos of the mechanical installs next…

c

[Dr_C2]

   

This is the 5500kV sensored brushless motor installed in the anglewinder configuration.

The motor will be operated at 7.5V suggesting a maximum rotational speed of 41,250 rpm.

With a gearing ratio of 31:13 (or is that 13:31?) and a tyre diameter of 20mm, this rpm corresponds to a linear speed of circa 18m/s. Well that’s the theory - actual speeds will be measured at the track using the new speed trap with digital read-out (as discussed here on a separate thread).

The idea behind the brushless project is to explore drivability of brushless motor driven cars at moderate speeds and then to explore the limits of the performance envelop at higher speeds.

The neat mechanical install should provide a good starting point.

c

[KensRedZed]

Looks very interesting.

13x31 gears with a brushless 40k motor? Make sure you install a hockey net at the end of the long straight. 

[Dr_C2]

or very good brakes?

c

[Drifter2]

Should be fun.  

Following.

[KensRedZed]

or very good brakes?

c

Actually the opposite. No brakes, and tons of speed.

If the motor spins 40k RPM at 7.5 volts. The wheel/tire would be spinning just under 17k RPM with a 13/31 gear. That's off the charts.

Ken