Stepper Motors

[cgmv123]

Electrical components become legal when enough of them are donated to FIRST to put an adequate amount of them in each kit of parts. If you want to use an electrical component, find a company willing to donate enough of them.

[nathannfm]

Originally Posted by cgmv123

Electrical components become legal when enough of them are donated to FIRST to put an adequate amount of them in each kit of parts. If you want to use an electrical component, find a company willing to donate enough of them.

Ha, sad, but true, I am sure that is legitimately one of the only deciding factors.

On a related note anyone want a bag of discontinued throttle motors

[dtengineering]

Now brushless motors in general... THAT would be a step forward. But steppers, in specific I don't think would be of much benefit to anyone.

Jason

[FrankJ]

More problematic than the motors are the controllers. You would need a source(s) stable enough to provide the same controller through one or multiple seasons for all the teams. The controller would have to interface with the roborio in such a way that the enable/disable is robust.

[Andrew Schreiber]

Originally Posted by dtengineering

Now brushless motors in general... THAT would be a step forward. But steppers, in specific I don't think would be of much benefit to anyone.

Jason

I'll be honest, I've spent some time trying to source a brushless motor for some non FRC projects and it's mildly daunting to find a motor and a controller. And then interfacing with them is a whole other issue (though I've found one that I can press fit WCProducts pinions (for bag motors) onto and do decent reductions)

[asid61]

Originally Posted by Andrew Schreiber

I'll be honest, I've spent some time trying to source a brushless motor for some non FRC projects and it's mildly daunting to find a motor and a controller. And then interfacing with them is a whole other issue (though I've found one that I can press fit WCProducts pinions (for bag motors) onto and do decent reductions)

I don't know, I've never had that problem. ESCs for standard brushless motors seem pretty easy to come by once you know what you're looking for. I'll second the gear problem though; you tend to have to use set screws or press fits to keep stuff on the shaft.
SDP-SI sells "fairloc" hubs for their gears, which are like integrated shaft collars that allow you to leave the shaft unmarred. Something like that would be good for interfacing a brushless motor.

[AdamHeard]

Originally Posted by asid61

I don't know, I've never had that problem. ESCs for standard brushless motors seem pretty easy to come by once you know what you're looking for. I'll second the gear problem though; you tend to have to use set screws or press fits to keep stuff on the shaft.
SDP-SI sells "fairloc" hubs for their gears, which are like integrated shaft collars that allow you to leave the shaft unmarred. Something like that would be good for interfacing a brushless motor.

Low cost, sensored, robust, controllers that go both directions without having to come to a full stop first?

[Jared]

Originally Posted by AdamHeard

Low cost, sensored, robust, controllers that go both directions without having to come to a full stop first?

The sensor part is really critical for brushless motors. Without a sensor, you get much less torque at low speeds, and you can sometimes stop in a place that you can't start from. I do think that brushless motors will eventually replace the motors we use now in FRC.

[techhelpbb]

Another way to use stepper motors is to put encoders on the stepper.
Then accumulated error is less and correction steps can be made.

That's basically what a closed loop MaxNC mill or router does on the axis drives:
MaxNC

If the goal is low RPM discrete movements over partial rotations steppers have a very valid use case.

If the goal is higher RPM discrete movements over higher numbers of rotations motors rigged to be servos make more sense.

In CNC case it is common that servo drives like those from Panasonic on my larger home brew tools are AC motors with encoders and for short low speed movements I need to use gearing or cog belts to get the speed down and the keep in the higher torque operational area of the servo. For occasional short movements it's okay to not gear down but honestly it is hard to just use the servo output shaft in most cases. Really same problem with FIRST drive trains and CIM motors. Stepper motors start to have decreased torque output the higher the output RPM where as servos tend to have higher torque in an RPM band higher up.

If my CNC work area is small, like say a 3D printer, it makes no sense to implement a full servo just so I can gear it down or do something with the electronics to push power into the motor and maybe blow past my intended target position. It makes more sense to use a stepper motor that tends to move slowly in discrete steps at higher power and catch the errors - with the extra bonus if a missed step is caught by the stepper with encoder it can be tried again which often works great with cutting tools pushing through materials.

Just to put it in perspective: servos with reductions can run at higher RPM with higher power than steppers so where professional larger size CNC is concerned (run time is directly proportional to production volume and money) I'd want the more expensive servos.

Course there's the short movement intermediate case of hobby servos. In the hobby servo case the target position and the desired kind of movement is more to be smooth and close enough. Also it was likely cheaper to make the plastic gear boxes in volume than create the electronics when those first appeared on the market.

Radio Control History

[Andrew Schreiber]

Originally Posted by asid61

I don't know, I've never had that problem. ESCs for standard brushless motors seem pretty easy to come by once you know what you're looking for. I'll second the gear problem though; you tend to have to use set screws or press fits to keep stuff on the shaft.
SDP-SI sells "fairloc" hubs for their gears, which are like integrated shaft collars that allow you to leave the shaft unmarred. Something like that would be good for interfacing a brushless motor.

That's the big issue. Once I knew what I was looking for in a controller and in a motor it became pretty easy to find things that would PROBABLY fit the requirements. [1] But a lot of the issues I ran into were because the specifications don't involve things like "torque" and "rpm" directly and instead involve new terms like "kv" and a handful of constants that I didn't know.



[1] Was looking sensorless brushless for cost reasons, ended up changing scale on the project and am using a pair of tiny brushed motors that, even with controller, come in cheaper than the motor.

[Michael Hill]

Originally Posted by Andrew Schreiber

That's the big issue. Once I knew what I was looking for in a controller and in a motor it became pretty easy to find things that would PROBABLY fit the requirements. [1] But a lot of the issues I ran into were because the specifications don't involve things like "torque" and "rpm" directly and instead involve new terms like "kv" and a handful of constants that I didn't know.



[1] Was looking sensorless brushless for cost reasons, ended up changing scale on the project and am using a pair of tiny brushed motors that, even with controller, come in cheaper than the motor.

So not really knowing much about Brushless motors (other than the basics of operation), what do they do better than the brushed counterpart?

[asid61]

Originally Posted by Michael Hill

So not really knowing much about Brushless motors (other than the basics of operation), what do they do better than the brushed counterpart?

More efficiency is a good one. Also more power density.

[Jared]

Originally Posted by Michael Hill

So not really knowing much about Brushless motors (other than the basics of operation), what do they do better than the brushed counterpart?

It's easy to tell a brushless motor to go at an exact speed, or to configure it to have a flat speed/torque curve. They also are generally more powerful/efficient for the same weight/size.

[AdamHeard]

Originally Posted by Jared

It's easy to tell a brushless motor to go at an exact speed, or to configure it to have a flat speed/torque curve. They also are generally more powerful/efficient for the same weight/size.

Yes and no.

It's not that they are inherently amazingly better for this, it's just that the typical control methodology required for brushless motors requires you to have your ducks in a row and already have the sensors/firmware required to do so.

[jman4747]

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA577582

Above is a study by the Army Research Laboratory comparing brushed to brushless motors for use in UAV's and land robotics systems. I like it because it talks about commercially available motors and practical concerns such as the fact that for consumer brushless motors the specs an engineer would need like stall torque, free speed, stall current, etc, etc. (what we are used to seeing for dc permanent magnet motors) are rarely if ever provided.