Brushless Makita Mod (unsupported)

I may or may not have already drawn a three piece o-ringed billet spindle body in Fusion. The top and bottom plates surround the bearings and should wick heat away very well.

Besides, this brushless motor doesn’t produce half the heat of the corded rt701c. I’ve run both in a small enclosed Nomad for hours at a time and have experienced the difference. Our spindle mounts are also very effective heatsinks.

I’ll take a torquey 8-36krpm all day once we get grbl to control it. What would be really nice is pushing the amps higher so that it has the same (or more) amount of power as the corded Makita.

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I had a feeling you might be up to something like that.

The total heat output losses are going to depend on the cutting load as well as the speed, if the spindle is water cooled then we’re mostly concerned with total heat load, if the spindle stays air cooled then we have the fan function to incorporate as well.
BTW, here’s a look inside at how a Chinese 30kRPM water cooled spindle is assembled.

The spindle load due to the fan is likely rising with the cube of speed (may be a little less, let’s not get into that) and the air flow volume will be going up approximately linearly with the speed. (edit there sorry, sorry, back pressure will be going up with the square)

This is why a ‘normal’ router spindle doesn’t really like being run at high cutting torque and low RPM, it just doesn’t have the airflow to dump the generated heat, when we get to high speed the limits become the winding current carrying capacity as all the cooling is available.

I’m really interested to see what could be done running a BLDC spindle with some useful display of real time cutting power on the Shapeoko.

If I have my ducks correctly aligned beak to tail;

  1. Spindle mechanical power (torque * RPM) is approximately proportional to cutting load
  2. Machine feed speed is preferred to be set from ‘feed per tooth’ for the cutter and therefore is proportional to RPM
  3. Depth of cut is constrained by machine rigidity, cutter vibration and spindle available torque at the given speed

So, given these things it would be useful to have a real time display of the mechanical properties of the spindle, RPM, and cutting power to assist in;

a) Understanding how hard you’re working the machine
b) Whether the toolpath has relatively consistent or large variations in cutting load etc.
c) Compare your expected cutting load based on material properties with observed cutting load

and maybe, if we can get all that working, for extra points;

d) Observe unexpectedly high cutting load to warn of dull or damaged cutters in a toolpath with a known cutting load
e) Feed back to the Shapeoko controller a feed speed override if the cut is consistenly low or high on cutting power to do what we do manually when watching the job run

Thoughts?

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Is that something you’d plan to machine on a large mill?

That’s what I’d expect, there’s a raft of reasons why a good BLDC beats a squirrel cage for efficiency.

Feedback thermistor here we come :wink:

I’m not familiar with the VESC controller, although it looks rather good. Is the idea to use the VESC to extract parameters and then to tune a regular ESC to run the motor or would the VESC be required permanently?

Given the efficiency of a modern VESC and the motor losses dominating the system losses if the RPM is known (extracted directly from the hall effect sensor?) and the DC power into the ESC is known we can use that to determine the motor electrical power and make some estimate of the mechanical power.

I am not sure how much of that would be possible with Carbide’s control board. It is based off GRBL which is very purposefully kept simple.

That said much of that functionality could be provided by an arduino and a small OLED screen. I found this very nice library for talking to a VESC over it’s UART interface:

There is a lot that could be done with this.

You could really use any proper spec ESC you want. I chose the VESC 4 because of the massive amount of feedback and tuning it provides as well as the fact that it could very easily handle the load. About the only thing that stinks is that it is limited by it’s ERPM rating (RPM * motor pole pair count). The VESC 4 is really meant for lower RPM loads like electric skateboards. The VESC 6 boards have twice the ERPM limit but they cost considerably more.

I was thinking of interfacing from the DC spindle controller back to something like CNCjs to do the feed overrides, would also be a useful way to send alarms and get the job paused if the spindle power goes out of expected range.

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Great thanks, so there’s an opportunity for others to follow the “early adopters” with some slightly more off the shelf hardware if the hack works well, that could be a nice outcome.

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Keep in mind that when I was searching (which I will admit was not exhaustive) an ESC that was proper spec (24V, high enough amperage, Hall Sensor support, etc) was about $50+. I think $25 extra dollars for the added features is well worth the price. Especially the added safety features it provides.

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I doubt that!

Got no load data at 8kRPM?

How much you’ll be able to get out of it depends a lot on how much heat you can get out!

Oh and you should be able to use a VESC on just about any of the brushless trim routers from the big box stores like the 20V Dewalt:

https://www.homedepot.com/p/DEWALT-20-Volt-MAX-XR-Lithium-Ion-Cordless-Brushless-Router-Tool-Only-DCW600B/305964582

Or the Milwaukee M18:

https://www.homedepot.com/p/Milwaukee-M18-FUEL-18-Volt-Lithium-Ion-Brushless-Cordless-Compact-Router-Tool-Only-2723-20/310179064

Or even some of the cheaper options like a RYOBI:

https://www.homedepot.com/p/RYOBI-18-Volt-ONE-Cordless-Fixed-Base-Trim-Router-Tool-Only-with-Tool-Free-Depth-Adjustment-P601/206955202

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I have honestly thought about building a custom VESC specifically for router moding which i can do because VESCs are open source hardware.

IMO motor current is far more useful than motor power because it will provide cutting torque. Dividing that by the cutter radius will then provide cutting force. Monitoring motor heat would tell you when the motor is being pushed to hard.
(The AC Makita is series wound(?) brushed universal motor.)

Their 1.25HP peak power claim is equal to that of the Makita and Dewalt AC trim routers.

So for the DC motors current ~ torque and the voltage rises with RPM to give overall power?

I’ve no experience with trying to track the output current of something chopping at ESC frequency, it would be a lot easier to have the ESC tell us that when it’s a smart unit like the VESC, for a regular ESC it might be easier to meter the input power to the ESC and do the maths with the RPM?

Oh right, I had a quick look and I thought the VESC started at $200+ , got any links for the cheaper ones?

I should probably also add, my comments about processing the data from the ESC weren’t a suggestion that somebody else should do that, my background is in analysing remote telemetery data so I can probably help with that :wink:

@LiamN: This is the one I am using:

https://www.amazon.com/gp/product/B07VL7D1WC

I am just saying that the Makita is not the only option for this hack, and the VESC’s flexibility and ability to tune to the various motor parameters is ideal.

Ah, excellent, I hadn’t seen that the hardware was GPL as well, that’s really rather good.