Experimenting with Sensored Brushless Motors

Experimenting with Sensored Brushless Motors - Printable Version

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RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 13th-Dec-24

With an Evo King brushed motor in a NSR F1 I managed a drag strip acceleration to 9.5m/s then a precision timed application of the brakes which brought the car to a smooth stop without reaching the emergency cushions. That was a few years back.

The 5500kV brushless motor posted above, in comparison, should have sharper acceleration and sharper brakes so I am hoping for a higher peak speed. Also, with a GT3 chassis there will be more opportunities to fit downforce magnets to reduce tyre slip. But let’s see.

c

RE: Experimenting with Sensored Brushless Motors - Kevan - 13th-Dec-24

(13th-Dec-24, 09:15 AM)Dr_C Wrote: more opportunities to fit downforce magnets

interest suddenly started waning...

RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 13th-Dec-24

(13th-Dec-24, 11:52 AM)Kevan Wrote:
(13th-Dec-24, 09:15 AM)Dr_C Wrote: more opportunities to fit downforce magnets

interest suddenly started waning...

Ha ha @Kevan,

We know that wheel-to-tyre grip and tyre-to-road grip can present issues with super-high angular acceleration motors. Adding downforce is a parameter which is easy to adjust and so will be :)

Don’t worry, any future GT3 drivability trials will be devoid of downforce magnets for obvious reasons.

c

RE: Experimenting with Sensored Brushless Motors - Kevan - 13th-Dec-24

I was pulling your leg Bigsmile

RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 14th-Dec-24

Henri from Badhoevedorp has kindly ‘long term’ loaned me one of his famous H&B test benches. This should be perfect for initial pre-track trials of the various brushless motor configurations.

Many thanks to Henri :)

c

RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 4th-Jan-25

Looking at my photo archive I see it was January 2019 when I first started running 1/32 scale digital slotcars with brushless motors. At the time they were sensorless brushless motors. The cars ran fast, no slow speed control and no brakes - they certainly needed some taming!

Wind forward six years and I’ve returned to the challenge.

The first sensorless trials will use a 7.5V DC powered track and the 4300KV 1625 motors. Theory says these motors should spool up to 32,250 RPM at 7.5V with full throttle. Measured with a tacho (i.e. in the real world) they read 32,800 RPM. That’s a difference of less than 2%, not a bad starting point.

Also, the ESC (electronic speed controller) which I am using has an option for proportional braking when the transmitter’s trigger is pushed rather than pulled. This is working nicely too.

Next step… full assembly onto the NSR Z4 then some testing using the H & B Test Bench. This will provide some rolling road m/s figures and current draw figures.

c

RE: Experimenting with Sensored Brushless Motors - Kevan - 4th-Jan-25

If you're using a proper RC ESC it might have drag-brake which enables you to brake without pushing the trigger into the brake zone. I always preferred drag brake when racing 1/12th RC cars as it was quicker than moving the trigger forwards for a fraction of a second.

RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 4th-Jan-25

(4th-Jan-25, 01:02 PM)Kevan Wrote: If you're using a proper RC ESC it might have drag-brake which enables you to brake without pushing the trigger into the brake zone. I always preferred drag brake when racing 1/12th RC cars as it was quicker than moving the trigger forwards for a fraction of a second.

Thanks Kevan for the input which I appreciate,

Yes - agree the ‘push for brake’ would cause braking delay on a fast slotcar track - but good in the short term for testing brakes. Later I can use the programming features of the transmitter to add the ‘drag braking’ effect you mention.

My brushless setup for the 4300KV motors only has very basic programming features on its matching ESC.

My brushless setup for the 5500KV motors has a more advanced programming card for setting up its ESC - so that might provide another option too :)

Hopefully some faster progress in implementing a fully brushless digital slotcar system than my earlier brief trials in Jan 2019.

c

RE: Experimenting with Sensored Brushless Motors - Dr_C2 - 4th-Jan-25

This experimentation is getting very interesting with some important laws of physics clearly coming into play.

First, it looks like tyres need to be glued and trued. ‘Obviously’ you may say… as the wheels turn faster, the centrifugal forces on the tyres increase, this causes the tyres to expand outwards and then jump off. So the next step is to apply some glue!

Also, the 5500KV motor at 7.5V, and with a transmission ratio of 31:13, is giving some impressive wheel RPM - I need to double check carefully before I report the numbers ;)

c

RE: Experimenting with Sensored Brushless Motors - Kevan - 4th-Jan-25

The RPM's reached will obviously depend on the length of the straight, you'd need a big track to get the max theoretical revs...or small diameter tyres.