Increasing CONTROL+ motor torque?

[SNIPE]

Hi,

I connected 4 CONTROL+ XL motors to a single robot inventor hub and used the robot inventor app to run them at 5% speed. It was fine other than the stupid app and hub cutting out all the.time (probably low battery). However I noticed that it takes like next to no effort for me to grab the wheel which the motors are driving and stop it rotating, then my program keeps running but the motors just give up permanantley and sit there.

Yes, I know I could run them faster and gear them down,

The problem with that is I need low mechanical noise and also gearing the motors would add friction (because  gears are gears) and a bunch of more problems that I best just leave out to not make this question confusing.

I know the motors definetley have enough torque because turning the wheel by hand without the motors running is harder than trying to stop the motors turning while it is running

So it's probably the motors overload protection kicking in as well as the fact that the stupid app and hub is not sending much voltage to the motors.

I can't see a code block to change the voltage, only the speed/duration.

So my question is how do I get  more torque out of control+ motors?

I have 2 buwizz 2.0 and dont yet have any buwizz 3.0. also have a ton of control+ bluetooth hubs

Regards, snipe.

 

[gyenesvi]

This is strange because I believe it should work as you wish it worked. The Lego Wireless Protocol allows the motors to be run in speed servo mode, in which it automatically adjusts the power (~voltage) as much it needs to maintain the speed (up to an adjustable max power budget, which can typically be set to 100%). Now the question is whether in the robot inventor app when you run them at 5% speed it actually runs in speed servo mode, or in regular PWM mode just giving it 5% power. But I believe we can't answer that without understanding the code behind the Mindstorms app, which we will never know.

Now first I'd definitely test it with properly recharged batteries. Second, maybe the 5% speed is too low for the whole speed control loop to work properly, especially for XL motors. I have noticed that it takes a bit more power to make them start moving than L motors for example.

I have made some quick tests with my custom desktop app that uses the lego wireless protocol to query/control hubs/motors. As the 5% speed seemed too low for this, I used 20% speed. When I set the motor to simple power mode, it's definitely very easy to stop the wheel connected directly to a single XL motor (I used an Arocs wheel, but its size does make a difference here). However, when I put it to speed mode, it got noticeably harder to stop the wheel, though still quite possible, but I feel that it's working against my hand. This may be useful as a comparison basis for your experiments to guess how the Mindstorms app may be working.

Also, note that the Mindstorms hub has ~7.2V batteries, while I'm testing with the Technic hub and 9V batteries.

Edited June 13, 2022 by gyenesvi

[Toastie]

3 hours ago, SNIPE said:

So it's probably the motors overload protection kicking in as well as the fact that the stupid app and hub is not sending much voltage to the motors.

I can't see a code block to change the voltage, only the speed/duration.

No idea what the robot inventor app does - as I don't have it.

However, I believe, for sure, that no overload protection kicks in here. It pretty much sounds like you are setting power (i.e. PWM duty cycle) and not speed (with whatever control loop implemented on the robot inventor system).

On the City and Technic hubs, 5% is really working fine with a PUp L motor. I don't have a PUp XL motor - but the control loop is for sure the same as for the L motor. When I try to stop the PUp L motor set to 5% speed, man, it freaks out. Needs some time (< 1s, so it is probably more P or PI rather than sharp PID) but it eventually freaks out, trying to maintain that 5% speed.

1 hour ago, gyenesvi said:

Now the question is whether in the robot inventor app when you run them at 5% speed it actually runs in speed servo mode, or in regular PWM mode just giving it 5% power.

Yes, that is the issue.

1 hour ago, gyenesvi said:

As the 5% speed seemed too low for this

Using an ESP32/Legoino client, 5% is no problem. As said, there is some notable time lag, but that's it.

1 hour ago, gyenesvi said:

Also, note that the Mindstorms hub has ~7.2V batteries, while I'm testing with the Technic hub and 9V batteries.

That needs to be considered, for sure, but PWM is far less prone to such "failure", as reported by @SNIPE.

Best,
Thorsten

[SNIPE]

Ok,

I fully charged the hub, now it is better, so I'll test it out properly soon and report back if there still is not enough torque.

Regards, Snipe

edit: I just realized that I will actually be using a control+ hub per unit, not a robot inventor hub but I need to buy 6 more AA batteries for the other c+ hub.

I am programming everything using the powered up app.

Edited June 17, 2022 by SNIPE