Ianhill said:
Iam geared at 11-54 giving around 4.9 final so I could gear down slightly but iam overvokting a 36v to 50v so dont want to strain it iam enjoying the go anywhere grunt I'll pop a video up soon to show brushed ain't dead just yet they still good for a tight budget, I only spent £250 for the price its heck of an acheivment.
Brushed isn't dead, but for a decent EV, they are not so wonderful. I think a top notch brushed motor is only good for 65% efficiency, while a BLDC can be 80-95% efficient and you get more torque for the same amount of energy consumed. I want as much of my wattage budget turning my wheels as possible. Look into getting an 80-100 outrunner at lunacycles. They are pretty strong motors. For about the same mass and size of your current motor you will get a LOT more torque for $150. I totally understand being on a budget! Over volting a brushed motor is just going to kill the brushes and stators faster. I bet if you looked at the motor under load the sparks coming off the brushes are significant. Basically use it until the motor is destroyed and then go brushless. I would plan ahead and start researching your next power plant solution now. Keep in mind that just about all motor controllers for BLDC that are designed for EVs need hall sensors. You get better performance out of a BLDC with halls in an EV than you do without them. You can use an R/C motor controller, but they are almost always over rated for the current they can supposedly handle. If I was going to use an R/C controller for an EV, and I found one that handled the cell count I wanted, I would then go for one that is triple the current handling of what I need. I'm running at 72 volts and 40 amps typically. That would mean the R/C controller would have to be rated for at least 120 amps at 72 volts before I would even think about using one. Look at the size of the heat sinks on an R/C controller vs one for an EV controller of the same amperage. Just the lack of heat sink material alone should tell you the R/C controller is way over rated. I like Kelly controllers, they are relatively simple to set up and use. There are a couple of things that they lack in the small EV realm...field weakening and phase current control are the two big ones. You can only set the controller current which is fine for protecting the batteries, but without phase current limiting you cant protect the motor or controller. Field weakening gets you an RPM bump with a very small loss of efficiency. Just about all better controllers have both of these.
just a couple of comparisons between BLCD and brushed motors...
1. BLDC motors for R/C or EV uses always use neo magnets. They are usually N50 strength. Brushed motors commonly use ceramic magnets that are N25 or weaker. This equates to significantly less torque for the same amount of current draw in a brushed motor. Rotation in a motor is all about interacting magnetic fields. Weak magnetic fields equals low torque. To make up for it, brushed motors tend to spin much faster than a BLDC.
2. BLDC losses are heat, winding resistance and magnetic flux losses. Brushed motor losses are 80% in the brushes and stator, heat, winding resistance and flux losses. Brushless motors completely eliminate the big loser in a brushed motor.
3. BLDC's come in two main "flavors"...inrunners and outrunners. An inrunner has the armature which holds the neo magnets inside the field windings. An outrunner has the armature outside the field windings. in either case the windings are fixed and the magnets rotate. A brushed motor has the windings and iron core on the armature and the magnets are fixed. This means the mass of the motor which is in the iron core and windings has to spin up to create torque. In a BLDC, there is significantly less mass in magnets and armature since there isn't all that iron and copper moving. This effectively makes a BLDC more responsive to spinning up and it has so much less mass of its own to move around.
4. A BLDC motor has no electro-mechanical failure points in it. This alone makes a BLDC much less likely to fail than a brushed motor. In a car alternator, which is effectively a brushed motor used as a generator, the primary failure point (70%) is the brushes. The other 30% of failures are regulators, diodes, windings and bearings. I don't know why car manufacturers don't use BLDC motors as generators. They are so much more reliable and less complex.
5. A BLDC motor is fairly immune to pollution (water and dirt). I don't recommend it, but you could run a BLDC in muddy water. A brushed motor will quickly destroy its stator and brushes since they slide past each other with no lubrication or way to keep the contact surfaces clean and smooth. As the brushes and stator wear unevenly, the contact resistance between them rises and more heat is generated which scorches the contact area more which causes more resistance. All the wires in a BLDC are insulated and enclosed so water is unlikely to cause a short. In a brushed motor the stator and brushes are exposed and shorts are more probable as a result.
6. I have a blower on my inrunner to keep it cool. I don't worry about a little dust or moisture getting into the motor and the bearings are sealed so I'm pretty much OK in whatever conditions I find myself. I would do everything in my power to protect a brushed motor from outside pollution including some kind of enclosed blower.
