Brushed vs Brushless

[Swede]

I am using logosol servo drivers which can use either brushed or brushless servos. Testing a large number of both types, it seems that the brushed servos are a bit easier to tune... the brushless PID parameters seem a bit more sensitive. Other than that, I can't see much difference.

What exactly is the benefit of brushless? Is it the maintenance aspect, no brush to wear, or is there some performance issue that I am missing?

Sorry if this topic has been flogged before, I couldn't find it if it was. Thanks.

Swede

[balsaman]

I believe it's the maintenance thing, and brushless are a little more efficient.

E

[Mariss Freimanis]

Brushless motors are thermally more efficient. This is because the windings are on the stator instead of on the rotor (armature).

Compare the ratio of stall torque to continuous torque for both types. Brush motors have a 5:1 to 10:1 ratio, brushless motors have a 3:1 to 5:1 ratio. These ratios reflect the ease with each can shed internally dissipated heat.

Mariss

[Al_The_Man]

Also be aware there are two types of brushless servo motors and drives, Sometimes refered to DC Brushles and AC brushless, there is basically very little between the construction of either motor, the difference comes in the type of commutation, DC brushless uses hall effect sensors to sense the armature position and the amplifier produces a series of pulses at the right moment to drive the rotor, the AC servo has more of a true sinusoidal drive and obtains rotor feedback via an encoder or resolver, the average torque of a DC brushless is about 5% lower than an AC brushless the peak torque however is around 10% higher.
One downside of the DC brushless is that it appears more like a stepper at low rpm, due to the pulse effect into the winding, whereas the AC servo is smooth down to very low rpm. this explanation is a bit simplistic but there is alot of infornmation on the various vendors web sites on this subject.
Al

[beegner]

Can you use a brushless motor on a Gecko 320 ?
Thank you

[Mariss Freimanis]

No

[panaceabea]

No the brushless will not work with the gecko. I talked with them just a few weeks ago about the subject. I was told they had a couple of prototype brushless drives in use but probably would not pursue due to the possible end user difficulties in tuning the drive.

It was explained to me via email by someone from rutex that the brushless servos with encoders were a lot more accurate than servos. Does anyone know of a drive for brushless motors down in the $100 us range?

[unterhaus]

Originally Posted by panaceabea It was explained to me via email by someone from rutex that the brushless servos with encoders were a lot more accurate than servos. Does anyone know of a drive for brushless motors down in the $100 us range?

I misread your post at first and thought you were talking about motors. I'll leave my first response at the end for completeness. There are RC hobby controllers for brushless motors for less than $100. They are sensorless. I'm not sure if they are using pic micros or what. And Rutex has a controller for $200 which is probably the cheapest. If it was easy to build a drive which will work for all brushless motors, there would be a brushless Geckodrive. You can do like I did, and buy them on Ebay. The AMC controllers seem to go for less than $100. http://www.a-m-c.com/ Not the most sophisticated drives, but they have a fairly wide application. But they aren't step and direction.

The cheapest brushless motors I have seen are around $500 US from Baldor. I would really like to find some less expensive ones for autonomous robot projects I have. You can easily get some high performance brushless on Ebay for less than $100 each. My limit is $50, but I don't need any more right now. As with anything on Ebay, you have to be careful, because 5hp motors are pretty common, and they are too much motor for most hobby machines. There are hobby brushless motors for significantly less than $100 for RC planes and cars, but these would be a little small for CNC.