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Motors and Rewinding
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Nick
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RS 550 Motor rewinding

Has anyone ever seen any tech info on rewinding small motors? I just spent hours on the web and came up with virtually nothing.

I want to get a 550 drill motor or a R/C racing equivalent working on 24 to 28 volts without blowing the brushes off or melting the armature. An 18V drill motor has 39 turns of around 22 AWG wire per winding - if I use more turns of lighter wire I should get the desired effect, but it will be pure guesswork without some theory and calculations.


I also went looking for a stock 24v motor, again without luck Sad. Mabuchi seemed the closest, but the RS775 RPM was way too low to work with a drill gearbox.
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Post Wed Jun 22, 2005 3:10 pm 
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Valen
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by my *rough* quackulations i'd think you would want about 50 (52) turns.
that(39) is a whole bunch of turns btw.

the hardest part of the winding process is the ballencing
you must balance the motor after you wind it, thats what the gree/white crud on the windings is.
if its not balenced then the motor works very poorly
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Post Wed Jun 22, 2005 3:33 pm 
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Nick
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Sounds good - I was guesstimating an extra 10 turns so we are very close. The main problem is that the armature was almost totally full with 39 turns, so I will have to go down a size or 2 in wire gauge.

The existing winding is 3050mm. @ 39 turns, the average winding length is 78.2mm, so 52 turns will be about 4066mm. I know the weight of the various gauges, and keeping the winding weight the same or less should mean the new winding will fit: old winding is 8.81g, so 4066mm of 24 gauge wire, weighing 7.78g should fit quite well...

The balancing part is harder - I think you can buy a balancer or get somebody to do it professionally. If I can get the winding right on a test motor, I may look at asking an R/C aftermarket place to wind and balance a custom armature.
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Post Wed Jun 22, 2005 4:18 pm 
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Philip
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Wouldn't the increase in impedance reduce the power of the motor?
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Post Wed Jun 22, 2005 6:37 pm 
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Glen
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in the old catalyst jeff ran the 9.6v drills at 12v off a 24v pack by putting two motors in series with each other IIRC.

that would be a perfect option for you nick except i dont think that its possible with the IBC. i guess its plausible if you just hooked a massive resistor in series with each motor but thats getting stupid really.

theres a little hobbyweight robot thats got two orion rc car motors run at something like 36v. ill get the link for you to get a look at. i believe he runs 45 turns.

http://forums.delphiforums.com/n/mb/message.asp?webtag=therfl&msg=2125.4
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Post Wed Jun 22, 2005 6:45 pm 
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Nexus
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Speaking of turns, does anyone know what it does to the motor to have double or tripple turns. Some hi performance car motors have 3 rows of 10 as a tripple 10 turn instead of a single 30 or double 15. hope that makes some sence, but anyway does anyone anything about this?? and what its supposed to do
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Post Wed Jun 22, 2005 6:54 pm 
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Glen
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reduce eddy currents maybe?? like how they laminate transformer iron cores. could increase the magnetic flux density as well?

do you mean they have 3 poles of 10 turns each or 3 layers of 10 turns on each pole?
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Post Wed Jun 22, 2005 7:01 pm 
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ffej
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" A "wind" is the number of wires that are used to wrap around the part of the motor that spins inside (called the armature). For Touring Car use, the most popular wind for a modified motor is a "double wind", meaning that two wires are wrapped around the armature. Stock 27-turn motors use a "single" wind, so only one wire is wrapped around the armature, 27 times. The lower the number of winds, the faster the motor reaches top speed and the more torque it has. The higher the number of winds (usually up to six), the slower the motor reaches top speed. High-wind motors are usually used to race pan cars. "

"Well, in plain speaking language it refers to number of times the wires are wrapped around the armature. A 13 turn double would be 2 strands wrapped 13 times. A 13 turn single would be 1 wire wrapped 13 times. The double wires have more torque where as single wires have more speed. In general, it means that more turns means more torque but less speed and vice versa. Thatís lower turns means lower torque and greater RPM. The number of winds describes how abruptly the motor accelerates. Fewer winds would mean less abrupt acceleration and more winds would lead to smoother accelerations."

So yeah, pretty much more winds = more torque and slower acceleration, but doesnt limit the top speed.
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Post Wed Jun 22, 2005 7:08 pm 
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kkeerroo
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I can't hold my tounge any longer. Increasing the winding will allow the motor to run at higher voltages, but it won't allow the bush springs to withstand that voltage. We have burnt out many drill motors and found that 90% of the time its the brush sprrings that go first. If I was you thats what I'd be focusing on first.
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Post Thu Jun 23, 2005 7:42 am 
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Valen
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i would have thaught the problem with the brushes? would be the current i^2R and all that jazz, so long as you arent actually arcing (which probbly may be somewhat increased though my bet is on it staying the same or reducing) . because you have an increased number of turns you are increasing the magnetic field strength of the winding (assuming you ran at the same current) this is offset (first order) by the increase in on resistance and increase the impedance (reducing top speed)
basically net effect is that everything should cancel everything else out.
at stall you would probbly have more torque unless you saturate the laminations.
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Post Thu Jun 23, 2005 10:16 am 
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Nick
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That's what I was expecting too - if the power output of the motor stays about the same, then the brushes should handle it. One difference would be that the higher voltage might cause more brush arcing.

In after-market 550 motors, the brushes have adjustable spring tension that (according to the advertising hype) allows more torque with heavy tension and more speed with less tension. Some motors also have larger commutators and they all have bigger brushes.

I am beginning to wonder if its all worth the effort; the power of an after-market motor is sure to be higher than a regular XU-1 and that means more broken gearboxes. I would just be moving the failure point closer to the wheels, rather than making the entire system more reliable.
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Post Thu Jun 23, 2005 12:12 pm 
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kkeerroo
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My brother (who did the previous post) doesn't quite understand why my motors failed. The brush springs (the copper bits holding onto the brushes) melted. This is caused by the current passing through the spring not by arcing between the brush and commutator. Re-winding the the motor to have more turns will increase the inductence of the motor and will therefor reduce the current passing through the motor at speed but will lower the top speed of the motor. Having more turns will also increase the magnetic field density (flux) of the coil and will therefor generate more torque thus keeping the overall output power of the motor fairly constant for a certain range of turns.
But to fit more turns on the armatures you would have to use a smaller gauge wire which wont be able to handle as much current if the motor stalls.
Another but is that a higher torque will mean that the motor is harder to stall.

My thoughts on the whole re-winding bit is that it will help but is way too much effort to go to for a cheap little motor like these unless you are really attached to them or don't have the money for something else.
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Post Thu Jun 23, 2005 3:53 pm 
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Totaly_Recycled
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If i was even to bother rewinding the cheap motors the first thing i would do is to get some small braid and conect it from the motor terminals to the back of brush holder .
It can be done as ive done it before but is extremly fiddly to do .This gives the current a less resistive path to follow instead of through the tensile brush springs which basicly lose their tension as thety get hot ,thus creating less tensoin + more arcing = more heat until they A --just melt or B they let the carbon brush drop out and it gets mangled up in the motor .

Post Thu Jun 23, 2005 4:19 pm 
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Nick
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Completely agree - you can't expect to get more power thru those tiny brushes an pressed springs. If I try a rewind & it works on the bench, the next logical thing would be to get a motor like this and rewind it:



This one has a bigger commutator to take the extra power. All of these motors have a metric boatload of marketing BS about all their supposed features and I suspect they are all pretty much the same for our intended use. Places like Tower Hobbies has many OK ones from around $30.

For robotics, it seems a motor with at bigger comutator, strong brush springs, and a stator with narrower gaps would be slightly better.
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Post Thu Jun 23, 2005 4:38 pm 
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Nick
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BTW Jake, if you are watching this thread: I came across some free curved NIB magnets that look like they would fit in a mini EV can. Would you like to try that? The extra torque could be impressive...
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Post Thu Jun 23, 2005 4:42 pm 
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