VESC in homemade lathe/drill press

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bollin
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Joined: 28 Nov 2017, 18:33
Location: Vasa

VESC in homemade lathe/drill press

Postby bollin » 28 Nov 2017, 19:01

Hello.
I am currently considering building my own lathe and drill press. I am thinking of using brushless DC motors for the projects. However I don´t know what I need in terms of ESC. This is the motor I´m intending to use:
Monster Power 160 (63M57)
Kv: 245Kv
Input Watts: 2700W
Resistance: .03 ohms
Idle Current: 1.45A
Continuous Current: 60A
Max Burst Current: 78A
Cells Ni-Cd/Ni-MH: 28-32
Cells Li-Po: 9-10
Weight: 22.8 oz (645g)
Overall Diameter: 2.5 in (62.8mm)
Shaft Diameter: .39 in (10mm)
Overall Length: 2.40 in (64mm)

That with a 24v dc power supply. I have read about another one who replaced his brushed dc motor for a Turnigy Aerodrive SK3 - 6374-149KV and a 24v 25A power supply. In another video I saw someone use the same motor but 24v 15A psu. How can one estimate the current drawn by the motors? I believe that it is however big enough so I can use it without it overheating.

I have been looking at a PSU rated at 24v 40A for this, and it should be adequate (and if others have managed with far less then I could use one with lower rated current).

The properties I need from the ESC is to maintain RPM under load, and RC helicopter ESC:s are recommended for that purpose.
I believe that the VESC is the way to go, but maybe someone else know better?

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TheFallen
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Location: UK
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Re: VESC in homemade lathe/drill press

Postby TheFallen » 29 Nov 2017, 08:54

The motor is 2700W, so to power it at +24V you'd need a 112.5A power supply.

However the 2700W at 60A rating they quote was obtained at +45V and I'd recommend a power supply that was closer to +45V than to +24V. This would mean the motor would run cooler and more efficiently. Also +48V server PSUs can be had for quite cheap.

e.g.
2700W = 24V x 112.5A
2700W = 36V x 75A
2700W = 48V x 56.25A

Of course I'm assuming the ESC will be 100% efficient, 80% is far more likely. Oh and a VESC is limited to 60A so a +48V supply will allow you to get the most out of your motor.

Therefore your parts list is:
  • Monster Power 160 motor
  • VESC
  • +48V ~70A PSU

bollin
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Joined: 28 Nov 2017, 18:33
Location: Vasa

Re: VESC in homemade lathe/drill press

Postby bollin » 29 Nov 2017, 17:22

Thank you for your answer. The reason I consider 24v is that 1 hp threadmill dc motors have been used successfully in mini lathes, and that equals about 750w. So, I will not be pushing this motor but rather limit it to 40A it will deliver 24v * 40A = 960w which is good enough for me. Or am I getting this wrong?

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TheFallen
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Re: VESC in homemade lathe/drill press

Postby TheFallen » 30 Nov 2017, 08:52

It ought to work out like that.

pf26
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Location: FR Valence

Re: VESC in homemade lathe/drill press

Postby pf26 » 30 Nov 2017, 11:00

From the data given, this motor can be run at max 10s or 36V, and this translates into 36*245=8820RPM (already quite a lot for a relatively large motor)
The continuous current is said to be 60Amps (most likely with good ventilation, because you have 0.03x60^2=108W joule losses inside the winding)
60 Amps * 36Volts = 2160 Watts continuous - I think 2700W would be only for very limited time...
30-40Amps should be fine (it still requires ventilation). You need to check the available torque then:
Kq= 30/(pi Kv): Kq= Torque constant.(units = N m),
Torque = Kq x I = 0.039 x I, that is 1.6Nm at 40 Amps.

bollin
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Joined: 28 Nov 2017, 18:33
Location: Vasa

Re: VESC in homemade lathe/drill press

Postby bollin » 30 Nov 2017, 19:28

Kq= 30/(pi Kv): Kq= Torque constant.(units = N m),
Torque = Kq x I = 0.039 x I, that is 1.6Nm at 40 Amps.

Where did you get the value of 30 from? Just asking for interest.
8800 rpm is too fast for my intended use, but if i could get a pulley system so i get 1/2 to 1/3 of that speed at the spindle im good, and then the torque increases as well.

pf26
Posts: 286
Joined: 28 Mar 2016, 14:37
Location: FR Valence

Re: VESC in homemade lathe/drill press

Postby pf26 » 01 Dec 2017, 18:13

Most likely 30 is 60 (secondes per minutes) divided by 2 (because there are 2PI radians per turn)..
Yes you probably need to change gearing to increase torque and reduce speed.
As for the current, most of the time it will stay low, unless you really need torque for hard work - And only then you need to make sure the motor is properly ventilated...

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC in homemade lathe/drill press

Postby rew » 02 Dec 2017, 20:30

Yes. The torque constant is actually the same as the motor constant Kv. Or depending on the units the inverse (*).

245Kv is 245 RPM / Volt = 245 (RPM/V) / 60(sec/min) * 2*pi (rad/rotation) = 25 rad/sec/V

That means the torque constant is 1 over that, or 0.04 Nm/a. So for 40A you get: torque = 0.04 Nm/A * 40A = 1.56 Nm.


(*) We normally mention RPM/V, but when you think of it as the generator constant, the number Volts/RPM becomes more logical. And in the proper units (V / (rad/sec)) it is identical to the torque constant (in Nm/A).

hackware
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Joined: 10 Dec 2017, 18:51
Location: backwoods mississippi

Re: VESC in homemade lathe/drill press

Postby hackware » 17 Dec 2017, 07:50

I have not found any other post with more information on specifics on motors...

if there is a better location, let me know...

I am a bit confused by some of the terms used here (i do have an electronics background)...

regarding a 2400W motor, 245Kv is used...

I my world of electronics, 245Kv would mean 245,000 volts...?!?

also, this forum refers to batteries by 12S, 3S, etc...

does that mean "cells", at 1.2V per cell...?!?

i've worked on electronics from radars to micro-hybrids, and have never come across such terms...

william...

ThierryGTLTS
Posts: 85
Joined: 09 Aug 2017, 11:10

Re: VESC in homemade lathe/drill press

Postby ThierryGTLTS » 17 Dec 2017, 12:09

KV, S, P,... Disturbing, isn't it :?: :!:

KV is a motor constant expressed in rpm/Volt.

S means series, P means parallel, for Li-Ions cells (about 3.6-3.7V/Cell).

Simple, isn't it ;) Have a look there for more infos http://www.electric-skateboard.builders/t/start-here-faq-for-diy-electric-skateboard-builders/215

Have a Nice Day.

Thierry


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