Why Hasn't first gone Brushless?

[Jeff K.]

One good thing about brushless is that they can come sensored, and extra encoders/sensors are not needed as the motor, tied with programming can precisely know its rotation or degree.

The brushed motors seen in these robots do not go through as many revolution in their lifetime as their similar counterparts in RC cars or in factory machines. These motors do not get to the point of maintenance that brushed motors usually require like new brushes or having the commutator cut. The maintenance of brushless motors in this case is unnecessary then.

Like Adam said, the motors we are given already are more than enough powerwise and efficiency wise for 2 minute matches, if designed properly. Races usually go at least 5 minutes up to 10 or even 20 minutes require brushless motors to last the longest and lipo batteries with huge capacities that do not start dipping until the last 1 or 2 minutes of the race.

These are smaller reasons of why they are not necessarily crucial to being in the KOP, but also because of costs. Brushed speed controller vs brushless and having 10,000+ motors. That would be a very generous donation as each motor would be at least twice the cost of a cim motor.

But to give brushless a fighting chance, motors and speed controllers have been getting cheaper. They could someday be cheap enough to make their way into the kits.

[Adam Y.]

Originally Posted by Jeff K.

One good thing about brushless is that they can come sensored, and extra encoders/sensors are not needed as the motor, tied with programming can precisely know its rotation or degree.

Most brushless motors are sensor less and that leads to another reason why not to use them. Sensorless motors are harder to start.

[Andrew Y.]

Originally Posted by Adam Y.

Most brushless motors are sensor less and that leads to another reason why not to use them. Sensorless motors are harder to start.

Cogging is what your thinking about, and this goes to cost again...low cost motors and controllers tend to have SEVERE cogging issues at low throttle

NEU 6pole motor with a MGM or Caste Creation MM or MMM can compete with many sensored setups. If i can get a 1500kv sensor less BL motor to go 0.2 mph on a crawler....Completely unrelated...i honstly believe sensorless BL motors will be the way...they are already proving to kick more butt on the tracks

[Adam Y.]

Originally Posted by Andrew Y.

Cogging is what your thinking about, and this goes to cost again...low cost motors and controllers tend to have SEVERE cogging issues at low throttle

That isn't what I was thinking of. Sensorless motor controllers work by measuring zero crossing point of the back EMF. If the motor isn't moving there is no back EMF which means you are essentially driving blind as to what position the motor to the windings.

[kamocat]

Personally, what I'd like is 3-phase motors. If you chose a motor within the correct speed and torque range, you need no gearing whatsoever, and can actually direct drive every wheel with its own motor. (crab drive with traction control, anyone?) There would be no need for a CVT.
However, there are some good reasons we haven't done this yet:

Luminary micro doesn't make a polyphase motor controller. While we could theoretically use 3 AC motor controllers to control torque, we would still require a variable-frequency 3-phase inverter to control speed.

AC signals can't be treated the same as DC signals. Calculating wattage and resistance is different, and you have to account for inductive reactance. Also, FIRST wiring standards would have to increase greatly to deal with 240v power.

I haven't investigated it, but I'm pretty sure 3-phase motors of a usable scale to us are mainly used on milling machines, and thus are upwards of $150 for the motor alone. This definitely isn't something FIRST can get for free.


Anyways, I figured I'd add my thoughts to the wish-list.

[Jared Russell]

Originally Posted by kamocat

Personally, what I'd like is 3-phase motors.

...

Unless everybody drags 120VAC extension cords all over the place, I don't think we'll be seeing 3-phase any time soon.

[Al Skierkiewicz]

Marshall,
Three phase (or polyphase) motors operate in relation to the way they are wound and the input frequency. Their greatest torque is at the speed for which they are designed. There is a distinct relationship between the number of windings/poles and the operation of the motor. When these motors are manipulated for speed, the controllers are adjusting frequency. The controller is essentially a large power amplifier. And they don't change speed quickly. In general when a person speaks of three phase motors, they are referring to power line operated devices used in locations where three phase power is available.

[Jimmy Cao]

There are so many problems with using 3-phase motors on FRC robots. Not the least of which is safety, having 120/240V around. I'm sure we'd all love to have kids wiring a high voltage system, which could rather easily kill them. I'm also not too familiar with inverters, but we would either need something that converts from 12VDC or have some way to store higher voltages (and then convert those to AC) on the robot, or have power lines leading to the robot (can you say "accident waiting to happen"?)

In my opinion, the safest, and most logical thing to do for FRC robots is to use some form of DC motors. Right now, brushed motors are being used due to logistics, and availability/price. Maybe, sometime in the (hopefully near) future, brushless motors could be used.

[Jared Russell]

While we're on the topic of allowable actuators, I would really like if we were allowed to use electric solenoid actuators. There are so many applications (dog-style shifters, brakes, clutches, latches, etc.) where I'd love to be able to eschew a full-size motor or piston, and where a servo just doesn't cut it.

[Al Skierkiewicz]

Originally Posted by Jared341

While we're on the topic of allowable actuators, I would really like if we were allowed to use electric solenoid actuators.

I wholeheartedly agree. There are a variety of great solenoids that eams could put to great use if allowed. Additionally, electrically operated clutches would be nice.

[kamocat]

Originally Posted by Al Skierkiewicz

I wholeheartedly agree. There are a variety of great solenoids that eams could put to great use if allowed. Additionally, electrically operated clutches would be nice.

I can't wait for the day when tool changers are a reasonable option on an FRC robot.

[EricVanWyk]

Originally Posted by Jared341

While we're on the topic of allowable actuators, I would really like if we were allowed to use electric solenoid actuators. There are so many applications (dog-style shifters, brakes, clutches, latches, etc.) where I'd love to be able to eschew a full-size motor or piston, and where a servo just doesn't cut it.

I was thinking the same thing a few weeks back. Do you know of any specific models that might fit?


On the AC motor "topic", thanks for the chuckles. Greg pointed out that it would make designing the PD a bit easier - just get a plug strip! Now we just need to find 3 phase AC batteries...

[Jared Russell]

Originally Posted by EricVanWyk

I was thinking the same thing a few weeks back. Do you know of any specific models that might fit?

Eric,

I'm sure that Al will know much more on the subject than I do, but I have used models from Pontiac Coil that are sold on DigiKey. Looking at DigiKey, most are in the $20-40 range and are 12V, .5-1.5" stroke, and offer holding torque on the order of a few to tens of ounces.

[artdutra04]

Let alone three-phase power on FRC robots, I just want [480v] three-phase power in my house!

There are tons of used (still in good condition) three-phase Bridgeport manual milling machines on eBay all the time within driving distance that are selling for $2k-$5k. Some even come with DROs! Who wouldn't want a full size manual mill at their house?

But the electric companies are like you're residential, grumble, grumble, single-phase 240v only, grumble, grumble, just use a rotary phase-converter, grumble, grumble.