Weapon ESC?

[Midge]

Hi,

I/we have built a heavyweight robot and are in the process of testing/refining the design and operation. We originally were using two Turnigy SK3 motors and VESC's. The spin up time for our weapon is too slow with this combination.

Space is a bit restrictive but I can fit larger Rotomax motors. I'm thinking about various speed controllers including a Turnigy K-Force 120A Opto but this does not appear to be current limiting. I can size everything to optimise the spin up time and keep the current within limits but am concerned about cooking the ESC's or Motor's from impact/stalling the motor.

Any constructive advice on this combination and worries about over current/stalling on these controllers or alternatives would be welcome.

Many thanks
Mike

[Niels - Team K.a.L.M.]

Quite often people will allow their belts to slip should the friction become dangerously high.

[Eventorizon]

What SK3's are you using and what settings do you have on the VESC's? Most obvious is what is your ERPM setting?

Very few hobby controllers have current limiting in them, they just dump power into the motor. The VESC's on the other hand can be to smart for their own good. If your SK3's are to high powered then the VESC's may not be able to handle keeping them in check or deliver the power they are demanding.

However, if you get your settings right you can make them do some impressive things!

EDIT - Nick [See below] makes a good point - I have a 160A 12S controller for my FW weapon!

[overkill]

Its hard to give you good feedback without knowing more about the weapon you are running. Many featherweight spinners already use ESCs of 120A and above, so you will need several powering a heavyweight weapon to be competitive.

[Midge]

Thanks for the replies - much appreciated. Agreed you need a bit more info.

Ok...the weapon is a 25kg mass of steel with 4 blades and a single cutting edge mounted either side with large bearings. Very free running and well balanced.

It is driven by two toothed belts and pulleys. The target motor rpm is about 6000 rpm to limit the tip speed on the weapon. ~3000 rpm on the weapon. The motors are turnigy sk3 6374 192kv, I am running 12S lipo system which runs at around 50V.

The VESC's are set to run at 50A max and erpm of 42000 in current mode. And the VESC settings are matched to the motors etc. The VESC's have uprated caps so should be ok at 12S.

The weapon does spin up very smoothly but slowly...

Hope thats enough !

Best wishes

[TechAUmNu]

Is this a horizontal or vertical spinner? What is the diameter?

For example most heavyweight horizontal spinners are 10+ kW and vertical spinners tend to not be that heavy. You currently have a max of 4.5kW with those motors and VESC current limit on 12s.

12s * 3.7V * 50A = 2220W per motor

ERPM will have no affect on spinup time, only voltage and current.

I suggest you work out the total kinetic energy at max speed, then use that to work out how big your motors need to be to achieve the spinup time you want.

Another solution would be to use some of the VESCs that can handle higher currents being sold on here. Which will be fine for 80A. http://www.fightingrobots.co.uk/thre...perage-version

[Eventorizon]

Those higher Amperage VESC's have Sold out for now. In short though VESC's are good for drive or lifters but not for spinning weapons.

To get the most out of what you have, set the ERPM to 80'000 and raise your max current to allow for bursts at start up, that should help it get going. Regular VESC's are not designed to run motors greater that 2Kw, and our up rated ones only just handle our 3.7Kw motors.