Brushless Weapon Drive system

Our bots have always used BaneBots brushed drive and weapon systems. But I have noticed that other teams are using brushless systems for their weapons and they are getting their weapons to spin extremely fast! I have a few questions about how to go about implementing this in our bots. I am looking at putting brushless in our bot Snake Eyes. For a look at Snake Eyes search Google for BartzTech and click on WBHS Robotics on the BartzTech site.

1. What BaneBots gear ratio would you recommend?
2. What ESC and motor would you recommend?
3. What would you recommend as a max RPM?

Thanks!

BartzTech wrote:

Our bots have always used BaneBots brushed drive and weapon systems. But I have noticed that other teams are using brushless systems for their weapons and they are getting their weapons to spin extremely fast! I have a few questions about how to go about implementing this in our bots. I am looking at putting brushless in our bot Snake Eyes. For a look at Snake Eyes search Google for BartzTech and click on WBHS Robotics on the BartzTech site.

1. What BaneBots gear ratio would you recommend?
2. What ESC and motor would you recommend?
3. What would you recommend as a max RPM?

Thanks!

any gear ratio
any 4 pole 540 size inrunner aka castle 3800 or china 2000kv or lower no traxxas motors. castle speed controls only mamba max pro prefered

max rpm i would say no higher than 45k it would wear the aluminum ring of the banebots gearheads very fast without a high pressure oil.

Should I run sensored or sensorless?

Thanks!

I believe sensored are preferred for drive, but depending on the weight you may could be fine with sensorless.

Jeff L wrote:

I believe sensored are preferred for drive, but depending on the weight you may could be fine with sensorless.

sensored would be optimal but very delicate unless you epoxy encase the terminals and the sensor ports. sensor wires and sometimes endbells with new ports get replaced by serious onroad rc car racers every race (2-6 hours of use) to root out sensor failures so i cant see them standing up to the abuse a sensorless can take. plus 4 pole motors don't cog unless you gear them close to 1:4.

the other downside to rc car race spec sensored motors is the 12mm standard rotors, they spool up fast but have next to half the torque of a castle 14mm rotor and get very HOT the airgap is huge and most companies that make sensored motors only have 13mm as the largest rotor size for sensored motors.

All the brushless weapons I've seen have NOT used gearboxes for speed reduction--belts and pulleys seem to be the standard. I've seen inrunner and outrunner, with the outrunners being a bit more common, probably because they have lower kv, so you start with a lower motor rpm and thus don't need a drastic size difference in the pulleys.

For instance, we had a 6lb disk, about 8 inches in diameter that was driven by a Scorpion HK-3026-1900kv and used a Castle Mamba Max ESC and a 4S LiPo. The drive pulley was less than a half-inch in diameter, and the pulley on the weapon was about 3 inches in diameter. The weapon was theoretically running at 4500rpm or so, with a tip speed of 150 feet per second. (if my memory is correct and I did my math right).

We had a little trouble getting the center distance right, and ended up adding strips of duct tape to the weapon pulley to get the belt to avoid slipping--and it worked extremely well!

for belt gripping try parma carpet traction for rc car foam tires it sticks belts to aluminum pulleys like glue and wont cause runout or friction from deflection.

You don't want traction aid on your inverted belts.

Get center distance and pulley sizes close, and then provide for some belt tension adjustment.

It can be as simple as a push pull setup. Bolts ppull and secure the motor, while set screws next to them provide the push/tensioning.

Use an amp probe and tach to make sure that tension is spot on. Amp draw should be low or within the specs of your motor, esc and battery specs, speed should be very close to as calculated, etc

This is engineering, Yes?

3 lbs. Sting used a Mamba micro motor/esc and spun its drum at over 40k, so anything is possible.

rjw (and it's good to see comments from you on here again), what did you use for measuring current?

Somewhere on this forum someone said that 1 foot of 10ga solid copper wire in series would drop 1millivolt per amp, thus you could (for VERY cheap) measure high current.

On the other hand, I have been considering buying a 'Doc Wattson' or 'Watts up' type data logger, but I'm not sure how much current they really can take, and if they are even worth the cost.

Main reason we want something to log current is to optimize battery weight/size, but it would also be great to get belt tensions to ideal ranges, as you have suggested.

rdubard wrote:

rjw (and it's good to see comments from you on here again), what did you use for measuring current?

Somewhere on this forum someone said that 1 foot of 10ga solid copper wire in series would drop 1millivolt per amp, thus you could (for VERY cheap) measure high current.

On the other hand, I have been considering buying a 'Doc Wattson' or 'Watts up' type data logger, but I'm not sure how much current they really can take, and if they are even worth the cost.

Main reason we want something to log current is to optimize battery weight/size, but it would also be great to get belt tensions to ideal ranges, as you have suggested.

Hi Bob

I use a fluke dc ampmeter.... not anything that actually installs in the bots