Paging JohnRobHolmes: Laydown brushes in CrawlMaster motor?

[fyrstormer]

As the title states, this question is for JohnRobHolmes, but the reason I posted it publicly is because the answer may be of interest to people other than myself.

When I first started my grand adventure into running brushed motors, I quickly found out about the existence of "standup" and "laydown" brushes. At first I didn't understand the difference, but once I actually got two motors with those different brush configurations in my hands, I was able to see that laydown brushes contact each pad on a standard 7.5mm commutator for a larger percentage of the armature's rotation, so each armature coil will stay energized for longer. This obviously means the motor will produce more torque, but I also noticed a big problem: Standup brushes already come close to touching opposite edges of the same comm pad, and laydown brushes actually do. That means there's a period of time during each phase of the armature's rotation where laydown brushes cause a transient short-circuit through the comm pad they are both touching. For a high-speed application such as racing, these transient short-circuits exist for such a short amount of time that the effects are probably insignificant. But for a crawler application where the motor may be stalled or nearly-stalled for several seconds at a time, these transient short-circuits could pose a serious risk of overheating the comm and/or burning the edges of the brushes. So I have stuck to running standup brushes in all of my brushed motors thus far.

However, after examining my new CrawlMaster motor, this problem doesn't appear to exist for a 5-slot motor. The comm is divided into 5 pads instead of 3, so each pad is narrower, and even the extra width of laydown brushes will never cause them to contact both edges of the same pad at once. So it would seem that 5-slot motors could benefit from the higher torque generated by running laydown brushes, without a significant risk of damage to the comm or brushes due to transient short-circuits at low RPM. Buuuuuut, the armature coils in 5-slot motors span 2 armature slots apiece, so the coils overlap each other unlike the coils in a 3-slot motor, and that may cause effects that I don't know how to predict using my meat-brain.

So, finally, my question: Is there any chance that running laydown brushes in a 5-slot motor, thus keeping each coil energized for longer, could cause the overlapping coils to end up "fighting" each other due to generating overlapping magnetic fields of opposing polarity? If the coils won't end up fighting each other at any point during the armature's rotation, then I'm inclined to try laydown brushes and enjoy some extra torque from my motor; otherwise, I'll stick to standup brushes like I've been doing thus far.

[Joshs4x4toyz]

To create a short of any sorts you would have to have a 2 slot armature where both brushes touch same phase and would stall. So you wouldn't have any overlapping with 3 or more simply based on a 360* circle. Its even even less with more slots (which is why there is less torque but smoother control). Also for this same reason you would yield more torque with a stand up brush.

So I guess to answer the question, no, no problems and they will not be fighting each other. But you would not gain any torque. I hope that helps, maybe I missed your mark completely and John will straighten me out too.

[Voodoobrew]

https://holmeshobbies.com/motors/par...s-laydown.html
You can test it out yourself. Just buy this $4 part and some laydown brushes for 7$.

Originally Posted by JohnRobHolmes

In the case of the five slot Checkpoint, cutting the trailing edge did in fact help performance because the brushes were too wide and overdriving the coils causing amp ripple.

Sounds like laydown brushes are not better in 5 slot motors. I think he really only ever has sold them in 3 slot motors for a reason other than not trying it out.

[JohnRobHolmes]

Laydown brushes should not be used on 5 slot. Too wide.

[fyrstormer]

Originally Posted by JohnRobHolmes

Laydown brushes should not be used on 5 slot. Too wide.

What would go wrong with wider brushes on a 5-slot motor? Not arguing, asking for detail.

EDIT: I see the quoted post from you further up, but I don't understand what "overdriving the coils and causing amp ripple" means. Can you explain or link me to an explanation?

[JohnRobHolmes]

The plane of commutation with a laydown is too wide for the 7.5mm 5 slot. It essentially drives the coils for too long, leading to some overlap time where coils are fighting. It basically shorts during a portion of commutation , which is the amp ripple.

What would go wrong, the brushes blow up and the coils overheat.

[Joshs4x4toyz]

See, I totally missed the mark I was thinking you were simply talking about a single phase shorting between your brushes (being wider). I see what you mean now about the coils on a single brush rather that the brushes on a single coil.....

So on the old cobalt pullers, did this have any affect? The Comms were pretty massive but so were the brushes. So, as long as your comm reached halfway from coil to coil or less you will benefit? More than that and you run into this?

[fyrstormer]

Originally Posted by JohnRobHolmes

The plane of commutation with a laydown is too wide for the 7.5mm 5 slot. It essentially drives the coils for too long, leading to some overlap time where coils are fighting. It basically shorts during a portion of commutation , which is the amp ripple.

What would go wrong, the brushes blow up and the coils overheat.

So I was right when I speculated that the coils might end up fighting each other during portions of the armature's rotation. Cool. Nice to know I wasn't pointlessly catastrophizing.

Regarding the plane of commutation (and thanks for clarifying that term, because I didn't know how to describe it): I already knew that with a 3-slot comm, laydown brushes are wide enough to touch opposite edges of the same comm pad at the same time, causing the amp ripple you mentioned (which I called "transient short-circuits" for lack of a better term), but I'm surprised to find out it also happens with a 5-slot comm. My eyeball caliper told me that wouldn't happen. Too bad.

So apparently there are two good reasons why laydown brushes won't work in my CrawlMaster. I have a small collection of laydown brushes and hoods from Tekin motors that I bought years ago, sitting in a bag waiting for a day that I can now be certain will never come. I guess I should just throw them away at this point. Yet another great idea ruined by the laws of physics. (I still haven't forgiven Einstein for proving that warp drive is impossible.) On the other hand, it means I'm already getting maximum performance out of my CrawlMaster, so that's less tinkering I need to do.