Motor Controllers for Models and Tools

[Michael GilliganParticipant @michaelgilligan61133]

So, Folks

What did you make of the TT Zero bikes ?!

MichaelG.

[John McNamaraParticipant @johnmcnamara74883]

Hi Neil

I am working on a small machine tool project…. It needs a small around 400 watt motor to power it ideally with a speed range at least 75% of full torque of about 750 to 4000 Rpm. Speed regulation is not very critical its not for CNC.

One solution is clearly a standard three phase motor and a VFD that works off 240V.

The following search for a 400 watt motor shows that in fact 400 watts is on the low side of what's available, some units of more than 2000 watts are available. in a very small package, although they require cooling at high power.

**LINK**.

Obviously this is a static machine and will not require a battery, however it will require a power supply.There are amazingly small PWM speed controllers available also available as found here:

**LINK**

Switchmode power supplies are also fairly low cost
Power supply

**LINK**

Or you could hack a larger computer power supply from the workshop come in handy stock bin.

I guess the tried and true industrial approach is the way to go. However the brushless model aircraft motors are considerably less expensive. Being brushless three phase there are no brushes to worry about. How one would stand up to use? some appear to have replaceable ball bearings.

I note one was used recently in a MEW drill project. Has anyone built one?. It would be good to get some feedback.

Regards
John

Edited By John McNamara on 06/06/2014 09:00:07

[Neil WyattModerator @neilwyatt]

Brushless motors are used in some of the newer mini-lathes and mills. They are a lot bigger than those on model aircraft. I think the latter are optimised for very high RPM, so things like engraving spindles and for use with small drills is ideal. Down to 750rpm, and you may find that they don't have the welly you need.

Neil

[Ian PParticipant @ianp]

I missed the one issue of MEW that supposedly contained the information on the actual motor and electronics but have had a little experience of using model aircraft motors for their original purpose (in an octocopter).

There is a very wide variation of motor types Internal/external rotor, sensor/sensorless, etc and obviously many different mechanical designs and configurations. Most are low voltage, in the model aircraft world they rarely state the voltage but just rate them in battery cells assuming everyone used Lithium batteries. Speed control is invariably by pulse width control rather than with just a potentiometer but that only adds a little extra complication.

The main problem is that these motors are built to weigh as little as possible and achieve their high specific power ratings usually for a limited period only (until the batteries are flat) Rating are peak values and bear no relation to continuous running so some means of removing heat will be needed and motors with an internal rotor are much easier to couple to a heat removing device than one where the windings are internal and have limited access to any cooling airflow. To drive a machine tool I would derate these motors by a factor of four.

The lightweight construction is also evident in the shaft and bearings and I doubt many would accommodate the load of any cutting tool. coupling the motor to a proper spindle will probably involve reduction gearing and a high ratio belt drive will need to be well thought out.

I have come across some very small but high power versions of these motors that are wound for operation off rectified mains voltage. The ones I saw were for powering underwater ROV thrusters so had the benefit of an infinite heatsink. (the ocean!)

Ian P

[Ian S CParticipant @iansc]

One place to get a DC motor of small size, and high power. You need to salvage one of those "stick" mixers (kitchen), they are about 600W, and there is a speed control built into the casing, about 30 mm dia. 60 mm long. The one I'v got is used as a generator on one of my hot air engines, gives a good current at 12 to 20 volts.

Ian S C

[Neil WyattModerator @neilwyatt]

> Rating are peak values and bear no relation to continuous running

Perhaps they sue something similar to the legendary Amstrad 'Music Power' rating for stereos?

Two good, reliable DC motors that are both cheap and powerful are the 545 (higher torque 5-pole version of 540 'buggy motor&#39 and the speed 400 which was universal for powered flight before BLDC became widely available.

Proops used to have some nice brushed motors by Buhler, a bit longer than a 540 with a torque ring, I have three lined up for an ASRL model.

Neil

[John McNamaraParticipant @johnmcnamara74883]

Hi all

Thank you for your thoughts.

A bit more digging…. A few people have used them to drive spindles. Although I am not building a spindle.

There is a good discussion here.
**LINK**

Or a general search:
**LINK**

Regards
John

Edited By John McNamara on 06/06/2014 16:05:05

[Neil WyattModerator @neilwyatt]

John,

Stephen Bonfield had an article on using an outrunner motor to make a drilling machine in MEW issues 209-213, in the archive and available as a back issue

Neil

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