Motors: Past and Future

[Lil' Lavery]

Originally Posted by Jared

I'd like to see a motor that was a little more powerful than the 775 but packaged the same way, so that it could be used instead of the CIMs for drive. The reliability of the CIMs is great, but they're really heavy compared to a 775, and not that much more powerful.

One crucial difference between a 775 and a CIM is how they're cooled. The 775s (along with 550s, AM9015s, FPs, Bosch drill motors, etc) are cooled via convection encouraged via the fan at the tail end of their shaft. That's why you don't want to stall these motors, since they need to be spinning at a relatively high speed to draw enough air to avoid overheating under load. The CIMs (along with MiniCIMs and BAG motors) are not cooled by fans, and instead rely on having a larger thermal mass to "absorb" the heat and prevent the motor from overheating. The heat is eventually dispersed via convection, conduction, and/or radiation away from the exposed surfaces of the motor (so having a larger surface area is important as well).

Since drivetrains often experience stall or near-stall conditions, it's important to have a motor that can survive stall or near-stall heating. Fan cooled motors are a poor choice for this (thus why so many Bosch drill motors failed back in the day). As a result, you need the additional mass to help these motors survive in a drivetrain. Of course, if you were to install some other cooling system this could be worked around, but I'd venture that the additional mass and space of the cooling system would outweigh the benefits.

I don't think you're going to get your wish.

[BBray_T1296]

The only improvement I could scrounge up about the CIM that would be quite beneficial was improving the heat release (body conducted heat away from the brushes faster/possibly incorporated a better heat sink, to make the motor more than just a 10% On 90% Off, perhaps up to a 50/50 or continuous duty without aftermarket passive or active cooling

[EricH]

My "dream" lineup for motors, current and past:

--CIMs (and variants--big, mini, bag), any combination but no more than 6 (Awright, quit complainin', 7).
--775s, 550s and the old FP motors (which were very similar), no more than 2 (maybe 4).
--Up to two Globe motors (need to specify allowed configurations, but those were very nice motors for light duty that was tough).
--Window and van door motors, no more than 4 total. For the right applications...
--Unlimited servos and VEX motors/servos (increase power on servos, though!)

--Additions: 2x brushless motors with speed controllers (restricted power/size, though, at least at first). The big thing here is that brushless motors are also known for not liking stalling, which would probably need to be pointed out to the teams.

[Richard Wallace]

Originally Posted by Lil' Lavery

One crucial difference ...

I don't think you're going to get your wish.

Sean has this exactly right. I am becoming more confident that he will be able to keep the Martian colony infrastructure operating smoothly, when the old timers of my generation are in our rocking chairs.

Just one point to add: power available from a motor falls off rapidly as the internal parts (i.e., brushes, armature windings, and magnets) get hot. This happens faster if the motor is smaller -- so even if a fan-cooled (e.g., 775) motor is nominally rated for more peak power than a totally enclosed non-ventilated (TENV) motor like a CIM, the TENV motor will deliver more power in all but the most intermittent of applications. Bottom line: stick to CIMs for your FRC drivetrain (duh).

[magnets]

Originally Posted by Richard Wallace

Sean has this exactly right. I am becoming more confident that he will be able to keep the Martian colony infrastructure operating smoothly, when the old timers of my generation are in our rocking chairs.

Just one point to add: power available from a motor falls off rapidly as the internal parts (i.e., brushes, armature windings, and magnets) get hot. This happens faster if the motor is smaller -- so even if a fan-cooled (e.g., 775) motor is nominally rated for more peak power than a totally enclosed non-ventilated (TENV) motor like a CIM, the TENV motor will deliver more power in all but the most intermittent of applications. Bottom line: stick to CIMs for your FRC drivetrain (duh).

I wouldn't say that as a blanket statement. Teams have been using 775's/FP's in drives for a long time. In 2003 and past, several of the Einstein teams, like 111, used non CIM's in drive, as you could only have two that year. Pretty much every team with swerve did the same Plenty of teams have also ran 2 CIM + 1 775 drives, like 254 and 118, which are both very successful teams.

With the available current monitoring feature on next year's PDB, stalled motors can easily be detected. It is true that a 775 will burn up quickly when stalled at 12V, but it can last a significant amount of time at 6V.

A minicim weighs 1.5 lbs more than a 775, and is less powerful. Given 1.5 lbs, I could add a decent heatsink and fan to a 775 for roughly the same total cost, and have more power.

Also, a more powerful 775 would be really useful in climbers/hangars, where you (ideally) never stall.

[asid61]

I like the way things are now. The only improvement I could see would be to use SSS-5940 10kw brushless motors in place of cims (they are the same size).
Oh, and raise the main breaker limit to like 600 amps.

[fb39ca4]

I'd love to see brushless motors.

[dtengineering]

Originally Posted by fb39ca4

I'd love to see brushless motors.

And you just beat me to saying it! Brushless motors are the next logical evolution... it is just a matter of getting the control circuitry down to a competitive price.

Jason

[EricH]

Originally Posted by dtengineering

And you just beat me to saying it! Brushless motors are the next logical evolution... it is just a matter of getting the control circuitry down to a competitive price.

Jason

Pretty sure that at some levels, it's down far enough. There's a reason electric R/C aircraft are becoming extremely common, and it isn't totally due to good batteries becoming more common/cheaper. The motors and ESCs also had to get cheaper. Admittedly, they don't often run on 12VDC, and typically have a "battery eliminator circuit" built in, but those can be worked around, right?

[JohnFogarty]

I'd love to see some brushless motors as well.

I'm not allowed to give any details at all at this point, but I know of a pretty big company looking at donating some pretty good motors to the KOP and FIRST Choice for next season. Only time will tell how substantial the introduction of these motors will be in the field of FRC.

[asid61]

Originally Posted by EricH

Pretty sure that at some levels, it's down far enough. There's a reason electric R/C aircraft are becoming extremely common, and it isn't totally due to good batteries becoming more common/cheaper. The motors and ESCs also had to get cheaper. Admittedly, they don't often run on 12VDC, and typically have a "battery eliminator circuit" built in, but those can be worked around, right?

ESCs (electronic speed controllers) for brushless motors do run on 12v actually, but it actually has to be 12v. Anything more than 12.6v and a little overhead should be avoided. This is because they are designed to be run on lipo battery packs. A 3-cell lipo has a normal voltage of 11.1v, but it's really 12.6v when charged. A lead acid battery like in FRC robots are 13.6v fully charged IIRC, which is a tad too high for a 3-cell ESC. It still might work, but you would have to check.
The voltage drop on the lead-acid battery over time might also be too much for ESCs.
ESCs are actually pretty cheap. Because they are often just SMD parts, I've noticed even cheap ones from places such as ebay work just fine due to the lack of manual work. If you wanted US-made ones though it could cost a bit more. They are usually cheaper than the controllers we use though.

[AdamHeard]

Originally Posted by asid61

ESCs (electronic speed controllers) for brushless motors do run on 12v actually, but it actually has to be 12v. Anything more than 12.6v and a little overhead should be avoided. This is because they are designed to be run on lipo battery packs. A 3-cell lipo has a normal voltage of 11.1v, but it's really 12.6v when charged. A lead acid battery like in FRC robots are 13.6v fully charged IIRC, which is a tad too high for a 3-cell ESC. It still might work, but you would have to check.
The voltage drop on the lead-acid battery over time might also be too much for ESCs.
ESCs are actually pretty cheap. Because they are often just SMD parts, I've noticed even cheap ones from places such as ebay work just fine due to the lack of manual work. If you wanted US-made ones though it could cost a bit more. They are usually cheaper than the controllers we use though.

There are plenty of hobby grade ESC's for brushless motors that would work at 13+ V that FRC sees. I have way too many brushless RC cars, and I design brushless motors at a my day job (at a company that also makes the drives for them).

They really wouldn't be much better than brushed motors, just more efficient. Since most of those drives are sensorless in the affordable price points, teams would see issues with cogging as most wouldn't know how to properly size them.

Most of the lower cost controllers handle direction change awful as well, and would only be suitable for flywheels, etc...

The true benefit of brushless motors for FRC would be when we get current control, which is a higher price point controller. We could do some REALLY cool control stuff at that point though, very smooth motion.

If hobby grade brushless motors became available for FRC, it's unlikely we would use them (reliability, the potential cogging issue). I reserve the right to change my mind after testing though. If anything we'd reserve them for applications that never see high stall loads and we can take advantage of their high power and efficiency in the faster range.

[asid61]

Originally Posted by AdamHeard

There are plenty of hobby grade ESC's for brushless motors that would work at 13+ V that FRC sees. I have way too many brushless RC cars, and I design brushless motors at a my day job (at a company that also makes the drives for them).

They really wouldn't be much better than brushed motors, just more efficient. Since most of those drives are sensorless in the affordable price points, teams would see issues with cogging as most wouldn't know how to properly size them.

The true benefit of brushless motors for FRC would be when we get current control, which is a higher price point controller. We could do some REALLY cool control stuff at that point though, very smooth motion.

If hobby grade brushless motors became available for FRC, it's unlikely we would use them (reliability, the potential cogging issue). I reserve the right to change my mind after testing though. If anything we'd reserve them for applications that never see high stall loads and we can take advantage of their high power and efficiency in the faster range.

The reason I said it won't work is because of the wide range. Many ESCs have cell detection and cutoffs at certain points programmed in. Hardware wise it wouldn't be a problem, but the software on the ESC might cause problems.

Power density might also help. The SSS 5940, which I was looking at for a go kart, has exactly the same dimensions as a cim, but it has a peak rating of 10000 watts versus the cim's 1600. I'm not sure if that's just the motor specifically or a property of all brushless motors.
Well, it has a stall current of 180 amps, but a voltage capacity of around 60v.

What is cogging? I've never heard that term before.

[AdamHeard]

Originally Posted by asid61

The reason I said it won't work is because of the wide range. Many ESCs have cell detection and cutoffs at certain points programmed in. Hardware wise it wouldn't be a problem, but the software on the ESC might cause problems.

Power density might also help. The SSS 5940, which I was looking at for a go kart, has exactly the same dimensions as a cim, but it has a peak rating of 10000 watts versus the cim's 1600. I'm not sure if that's just the motor specifically or a property of all brushless motors.
Well, it has a stall current of 180 amps, but a voltage capacity of around 60v.

What is cogging? I've never heard that term before.

The same ESC's that have low voltage cuttoff that can't be turned off are usually also the ones that don't handle direction change nicely, so none of those would really be an option anyway.

That 10kw number is likely peak electrical, MOST cheaper brushless motors (RC grade stuff) is vastly overrated in power because they spec peak electrical power, and the motor would burn up at that operating point anyway. As you pointed out, this big power comes at higher voltage in most cases. You won't find an RC grade brushless motor at 12V pushing more than 1kw (if that) commonly.

If we were to go to brushless, I think the right move would be a custom controller adapted from industry to be cost effective, and possibly a modified RC brushless motor that is fully sensored. Industrial brushless motors are just too expensive for FRC currently.

[Mk.32]

Originally Posted by asid61

The reason I said it won't work is because of the wide range. Many ESCs have cell detection and cutoffs at certain points programmed in. Hardware wise it wouldn't be a problem, but the software on the ESC might cause problems.

Power density might also help. The SSS 5940, which I was looking at for a go kart, has exactly the same dimensions as a cim, but it has a peak rating of 10000 watts versus the cim's 1600. I'm not sure if that's just the motor specifically or a property of all brushless motors.
Well, it has a stall current of 180 amps, but a voltage capacity of around 60v.

What is cogging? I've never heard that term before.

Did someone say Brushless RC motors and gokart, with 48v LiPo pack?

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