Drive motor options

[maddox10]

We use the 18A trackstars for the experiment, neat little speedo's.

[Liftoff]

We're seriously considering the brushless drive, my brother is in contact with a local roboteer who successfully used a similar setup on his spinner at last year's event. So as soon as he's confident its doable I'll start sourcing the parts... We're looking at these motors and esc... they do look like an overkill but what the heck, as long as they fit inside !
Will be testing the gimson gearbox, if it survives good, if not then there should be alternatives me thinks

motors
http://hobbyking.com/hobbyking/store...0KV_1295W.html

and escs
http://hobbyking.com/hobbyking/store...s_Car_ESC.html

[Ellis]

Am skeptical but only because it's in my nature, wish you both good luck! If you manage to get decent response times from biggish brushless motors like those then you'll be paving the way for many.

(just don't expect the gimsons to handle 1.6hp for long!)

[leorcc]

I have that ESC in one of my truggies. It works great, just keep away from water. For the function you need, you need to program it with the transmitter. The programming card will not set the reversing correctly.

[Daniel]

Hi guys. I notice my robots are being talked about.
I have been building a brushless drive feather and I did take it into combat but failed. The brushless motors and controller worked perfectly, it was the lack of money that forced me to make a dodgy drive train that was the problem. Sprockets slipping, chains coming apart, motors falling off, stuff like that. The 4WD test platform does work reliably, as show in the videos.
I used the 80A Trackstars as they were the biggest car brushless controllers on Hobbyking last year. That was fine with me as I think that the NTM 42-38 750kv motors are the biggest you will need for a feather weight drive, but that is just a personal opinion. I do run a 4 cell LiPo to try to get the most of the 750W the motors are claimed to out put. When working they produce a very simalar driving experiance to running 2 x 300W scootor motors in a feather weight, and since I know a 300W scooter motor can output closer to 500W, then a 750W brushless motor is probably closer to 500W when used for drive. But that is just eye-balling the robot driving around, so who knows.
The 150A Trackstar is a new product on Hobbyking, but it looks the same. I didn't need to spend too much time mucking around with setting on my 80A controllers and they robot drives the same as the old scooter motor / Victor 883 setups I used to use. If I ever get a job I'd like to try the new 150A Trackstar and a NTM 50-50 on 6 cells to drive an axe. An all brushless Avenger.

[Ellis]

Thanks for the info Daniel! Is there really no delay between FWD/REV? I guess it's quite like having a braking function on brushed motors, but that gets bypassed (I believe) if you're ramming back and forth, and the polarity just switches. With brushless there must be an extra delay to allow the motor to stop completely before continuing in the opposite direction?

Would you say it's responsive enough for a robot which is all about drive control - i.e., a design something like Sewer Snake's, where being the dominant driving force in the arena is kinda crucial?

Could be the future of this sport!

edit: I mentioned Hot Stuff a page back, I am now fairly confident that that is running four of these: http://www.hobbyking.com/hobbyking/s...tor_730KV.html - spotted the red and black motor cans in one of his videos. That's a lot of power!

[Daniel]

I don't notice any pause when switching directions. Maybe someone else who is a lot more anal would but I felt it was the same as an IFI. I'll find the instructions and post what setting I used once I remember.
I also think it's the future and surprised I hear people saying outrunners won't work for drive.

[Daniel]

Found the Trackstar 80A instruction manual. There's a few things that arn't actually listed on the hobbyking webiste such as it is rated for motors < 2300kv. Also the controller can be reprogramed for brushed motors but I don't know how well that works. Here are the 9 programing options and what I chose:

1) Brake/Reverse type - 1. Reverse Lockout - Allows reverse only after 2 second pause at neutral throttle
. 2. Forward/Brake Only
. 3. Forward/Brake/Reverse - What I chose. Reverses as soon as motors brakes to zero rpm.
2) Brake Amount - I set this at 100%
3) Reverse Amount - You can chose 25%, 50%, 75% or 100%. 50% was default, so I changed to 100% or I'll drive in circles.
4) Punch Control - Basically has settings for acceleration - High, Medium, Low, Lowest or disabled. I think I had it disabled.
5) Drag Brake - How much braking when the motor coasts. I might have screwed up and set one motor at the highest, 40%, and the other at 0%. Didn't effect driving much.
6) Throttle Dead Band - The largest is 0.1500ms, default is 0.1000ms and the smallest is 0.0250ms. I left it at default because I didn't quite understand what would happen if I changed it and it seems to work as is. The largest would give more kick to start the motor but lower gives more control.
7) Voltage Cutoff - I left this default at Auto-Lipo, for obvious resons.
8 ) Motor Timing - You can select lowest for efficiency, highest for increased power, normal as default. I think I left it at default.
9) Motor Type - Brushless, Brushed Reversing or Brushed high power. I left this as brushless.

So it seems that for one of the controllers I only changed setting 1) reversing, 2) max braking and 3) 100% reversing. Took a bit to understand how to program it with a pistol radio, but wasn't hard once I understood the instruction's chinglish

[Ellis]

Brilliant information, thank you! Well now I feel a bit of a fool, seems this is already entirely possible. I'd still expect a good old brushed system with a set of BB TZ85s to be more reliable at this point, but this certainly sounds viable now.

Cue everyone using brushless for the '14 champs, lol.

[Eventorizon]

Is there actually much benefit to running a brushless drive? The initial weight saving and power increase from the motor is obvious but with all the chain you had to add to get the necessary reduction There may not have been much weight saving. Is there anything to my logic?

It also crosses my mind that if you took a banebots gearbox, for example on 16:1 or 25:1, could it cope if you mounted a brushless motor to it?

EDIT: That said the motors on the test machine are only 750kv where as the 775's are over 1000... maybe its not an issue

[Ellis]

It's a misconception that brushless motors are all super fast. Many many examples are significantly slower than traditional brushed motors. The big-gun brushless outrunners are almost inconveniently low revving.

I imagine a 16:1 p60 banebots gearbox would handle a brushless up to say 1kw peak power, beyond that the torque involved might be a bit risky? Never worked with them so don't know how tough their insides are.

[Liftoff]

The Ntm 4248 motor does around 12000rpm at 5s and 1300w, good for the given weight and size of the motor. Thats almost half the speed of a gimson or banebots so it's not going to over rev a gearbox.
The problem I'm seeing is that it will probably need a custom gearbox as I have yet to find a 10:1 ish box. If I still don't find one will have to build my own
Another plus I can think of is the relatively cheaper price of the esc when compared to a brushed one.

[daveimi]

I think a few people are coming up against the same problem (I know I am) i.e it's easy enough to get hold of a decent motor, but then trying to find an off the shelf 'box to fit is nigh on impossible.

[Liftoff]

That's very true David, however it's not too difficult to construct a simple gearbox with 10;1 ratio me thinks...I mean the motor speed is not that fast so the no of gears required is low and normal off the shelf bearings will do.
Have to start looking at some gear selling shops to get an idea of dimensions etc tho...

[maddox10]

I fitted 2850 Kv Brushless motors to Gimson GR02 24-1 gearboxes, all it took was drilling 2 3.5mm holes at the right spot.