Motor recommendations

[mutant]

my series motor has seen over 9000rpm....since jonnieB enlightened me to that fact it no longer sees those rpm`s....so i think the listed manufactured rpm`s are a safe rpm-but some may live well past that......
i no longer tempt the rpm devil-lol

[JohnnieB]

Originally Posted by mutant

my series motor has seen over 9000rpm....since jonnieB enlightened me to that fact it no longer sees those rpm`s....so i think the listed manufactured rpm`s are a safe rpm-but some may live well past that......
i no longer tempt the rpm devil-lol

The RPM listed by motor manufacturers and sellers are typically the RPM the motor's max HP is rated at and tend to be more mid-range rather than max sustainable RPM.

Due to liability concerns, getting the manufacturer to state a max safe RPM is akin to pulling teeth and if you get them to give you a number, it will likely be a conservative number. In my communications with D&D, I got two numbers for an ES-76-51 motor, 6000RPM from Vic and 6500RPM from Eric. Needless to say, I use the higher number and I used to exceed that fairly often.

With my shorter than stock tires (17" tall) and a 42V battery pack, I can exceed 7000RPM on level ground, but I seldom have the need (or desire) to go faster than 25 MPH, so the max RPM set in my XCT is 6500 RPM, which is about 26.5 MPH with my tire height.

Attached is a picture of the series motor from a 1986 EZGO 3-wheel cart. It says the Max safe RPM is 8000RPM.

Ironically, over-revving the motor isn't an issue for most cart owners since the first modification seems to be installing taller tires and the taller the tires, the slower the motor turns at any given speed. In addition, taller tires change the final drive ration and the motor can no longer reach the same RPM it did with stock height tires, unless the battery pack voltage is also increased. In a nutshell, it is only us nuts with relatively short tires (IE 20" or less) and higher than stock voltage battery packs that push the RPM envelope.

[yurtle]

Is it simply the RPMs that can kill a motor or is it a combination of high RPM, followed by letting off the gas, which "overdrives" regen? I'd expect the bearings are affected by RPMs and nothing else? That would really mean the differential is just as stressed by high RPMs as the motor (which only has one bearing).

I know heat's a killer, and have warning and danger LEDs for that.

[Conradconrad]

ScottyB does you D&D motor use the speed sensor ? Otherwise how does your XCT obtain rpm data. Also is it able to limit rpms going down hill?

[JohnnieB]

Originally Posted by yurtle

1. Is it simply the RPMs that can kill a motor or is it a combination of high RPM, followed by letting off the gas, which "overdrives" regen?

2. I'd expect the bearings are affected by RPMs and nothing else?

3. That would really mean the differential is just as stressed by high RPMs as the motor (which only has one bearing).

4. I know heat's a killer, and have warning and danger LEDs for that.

1. RPMs alone can explode an armature, but if the armature is well balanced and strongly built, it takes a lot of them. Add the stresses of excessive heat and the physical forces imposed by strong regen braking to the equation and the armature will explode at a much lower RPM.

2. See page 80 of attached pdf.

Just because the bearing fits, doesn't mean it is the right one for the job.
Also, the bearing on the motor shaft ought to be a hybrid type (steel races with ceramic balls) since it is located within the intense electromagnetic fields generated by the armature and stator.

3. Only the input shaft spins at the same RPM as the motor.

4. You got that right.

[yurtle]

Thanks. I assumed that since the old series motor you posted said 8,000 max RPMs, it could be pushed beyond that.

[JohnnieB]

Originally Posted by Conradconrad

ScottyB does you D&D motor use the speed sensor ? Otherwise how does your XCT obtain rpm data. Also is it able to limit rpms going down hill?

I'm not Scotty, but my D&D motor does have a speed sensor, which is connected to my XCT-PDS controller.

The XCT reduces the duty cycle of the output to 0% when the max RPM it is set to is reached, but I'm not sure if it turns on regen braking to keep the motor's RPM down to the setpoint like the stock PDS controller does. I suspect it does, but I've never tried it since I've lowered the setpoint to 6500RPM, nor did I ever go down a steep hill at full throttle when it was set at higher values.

[JohnnieB]

Originally Posted by yurtle

Thanks. I assumed that since the old series motor you posted said 8,000 max RPMs, it could be pushed beyond that.

If I was planning to run a cart motor much above 8k, I'd have it high-speed banded and critically balanced as well as installing hybrid bearings on motor shaft and differential input shaft since it is not fun sliding to a stop from ~35 MPH with deep ditches and barbed wire fences on both sides of a narrow road.

[skipsmith521]

My cart with 36volt and XCT400 get to 25 or 26mph clocked with a GPS. In our neighborhood we have one of those MPH boxes that clocks your speed in hopes you will slow down. It clocks my speed at 25 or 26 sometimes.

I paid for high speed banding on my motor, but I guess with the RPMs I get...it doesn't​ matter much.

Not sure if my thinking was right on this, but I paid a little extra for the high speed banding...as I thought since a DCS doesn't have speed sensor, it might help a little if my teenage son found a little hill and went full throttle.

Skip



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[JohnnieB]

Originally Posted by skipsmith521

My cart with 36volt and XCT400 get to 25 or 26mph clocked with a GPS. In our neighborhood we have one of those MPH boxes that clocks your speed in hopes you will slow down. It clocks my speed at 25 or 26 sometimes.

I paid for high speed banding on my motor, but I guess with the RPMs I get...it doesn't​ matter much.

Not sure if my thinking was right on this, but I paid a little extra for the high speed banding...as I thought since a DCS doesn't have speed sensor, it might help a little if my teenage son found a little hill and went full throttle.

Skip

Sent from my Nexus 6 using Tapatalk

Fortunately my youngest boy is 47, but I do remember making similar decisions.

The banding might come in handy if cart is towed home by one of his friends.