Brushless motor control

[mightymouse]

have a brushless motor and controller but concerned whether the regen effect of a disc slowing will damage the controller.

If the motor connections go through a relay to make contact when running, but break contact when not powered allowing the disc to free-wheel, will the sudden loss of contact through the controller also damage it?

Trev

[grant_ploughbot]

Re: Brushless motor control

Hi Trev,
It I'm looking into this at the moment for my new robot (not a spinner though but works in similar way). The ideal route for a spinner would be to have hefty one way bearing or clutch that can disengage, however alot of people don't seem to have too many issues without. I might go the clutch route for mine.

[typhoon_driver]

Re: Brushless motor control

You can include a clutch mechanism in your disc if you use a timing belt with a timing pulley on the motor. Then just use a smooth pulley on the disc. Works for the guys in the states

[mightymouse]

Re: Brushless motor control

A one way bearing would be more suited to the type of disc and there is no danger of regen. Will make one if I cannot find anything off the shelf.

Looked at smooth belt drive Gary but tensioning would be an issue, there will be a lot of inertia to overcome on a dead start.

Thanks

Trev

[Mouldy]

Re: Brushless motor control

I did the one way bearing idea... bearing fell apart on a big impact... the loading for a one way bearing is alot lower then that of a normal one of the same size... little spinner do ok but they have quite a big gear ratio after the bearing so less loading on it...

Im using the toothed drive pulley on the motor, smooth pulley on my drum option at the moment in 720, and ive tried quite hard to break it and i havent... only thing thats broken are drum teeth and a motor coming loose because i didnt loctite it up.... you'd be suprised how easy it is to tension it trev, just make it so if you hold the disc... you can turn the motor output shaft by hand and it spins the belt, but with a bit of friction...

Also adding additional capacitors to the esc really helps, ones with a low ESR value- lots of information on this on the web if you google it.

Did consider having a contactor inline with the motor/esc but it just seems a lot of weight for something with the right current carrying capability that can be overcome by something else.

Also; dont mount the esc properly lol.. sounds daft but everytime i have the big impacts have damaged it...LS4 found the same... wrap it in foam and cable tie it down so its got some movement.

[mightymouse]

Re: Brushless motor control

Looks like it is 2:1 smooth final drive pulley with toothed belt then.....

Thanks for the info lads.

Trev

[grant_ploughbot]

Re: Brushless motor control

Is this a disc or a bar? and what sort of Dia?
2:1 will be spinning pretty quick on the motor your using wont it? On NST we are running just over 2200rpm or there abouts. Much quicker and it throws itself out the arena! If its on a bar I wouldn't gear for more than 3500rpm. If your running a 550kv or similar motor on say 10s I would look at atleast a 5:1 ratio

I was considering using one of these in mine, http://www.kasama.co.uk/helicopter-spar ... -pack.html
Although that one is abit pricey. Its a Tsubaki one way bearing, amazing quality and in big heli's I've crashed them alot and never had one lock up compared to the cheaper versions.

[Eventorizon]

Re: Brushless motor control

We have a clutched bearing fitted to Binky but it is not a main support bearing; the main load is taken by two huge deep groove bearings at either end. As Sam explained it to me, its fine to use them so long as they are not the primary support bearing. But I guess we will find out.

[mightymouse]

Re: Brushless motor control

Grant; meant 2 votes for smooth pulley/v-belt and 1 vote for one way bearing.

Will be gearing to around 2-3000rpm, the disc is a 24 x 3 x 10mm thick solid titanium bar provided by Swanny(who else) for Ironside2 - hence the high inertia on startup worries - Swanny will be driving.

Suppose I will have to build it to really know. Will construct the disc mounting such that the drive is not integral to the mountings, then can swap between smooth pulley and one way bearing.

Trev

[grant_ploughbot]

Re: Brushless motor control

Haha, that makes sense now Trev!
Big nipper guy's do use a cheaper one way bearing. It sometimes locks up but the majority of the time works fine as they turn the power off just before they hit something. That saves alot of the issues your thinking about. They use it directly on the end of the motor shaft. I'm still considering a few options for myself - working out how on earth I can put 11kw of brushless power into an axe and make it work reliably! I look forward to seeing it!

[craig_colliass]

Re: Brushless motor control

Just a thought I had.
Has anyone made a bar spinner with a propeller profile so when it has spun up it pushes the robot to the arena for better traction and makes it less likely to throw itself OOTA!

[grant_ploughbot]

Re: Brushless motor control

That was discussed at the Robo Challenge Open Day.
The aero dynamics of a bar make a huge difference to the current draw. Simply profiling the edges can take the current draw down from say 80A constant to way below 40A. Providing enough downforce is likely to take a good couple of Kw to do effectively.

[typhoon_driver]

Re: Brushless motor control

Problem with that would be if the profile gets damaged it wouldn't provide the same downforce. Much better to just use magnets in the robochallenge arena.