General => General Robotics Discussion => Topic started by: 65fastbackmaniac on September 05, 2016, 09:43:05 pm

Title: Getting the right motor gear ratio in a 1lb/3'b
Post by: 65fastbackmaniac on September 05, 2016, 09:43:05 pm
So I just got back from the fights at DragonCon and my bot was way to slow. I know I screwed up on the gear ratio of the motors I bought so before I go and buy new motors I want to make sure I get the right ratio this time. I was running 50:1 silver sparks. It was a sumo bot kit with a spinner put on top. For the complete redesign I'm trying to make one of the 3 wheel spinner bots what would be a good ratio to go with, or what do I need to look at to decided on the motor ratio.
Title: Re: Getting the right motor gear ratio in a 1lb/3'b
Post by: Coboxite on September 06, 2016, 06:12:35 am
You need more speed. The highly geared motors are fine for sumo, but make you easy pickings for much faster wedge and drum bots. You can up the speed considerably by dropping the gear ratio(20:1 Goldsparks or 11:1 Sliver sparks for example).

Getting the "right" gear ratio also depends on wheel size. 1"-1.5" is best for the 11:1 Sliversparks, but are too small for a 50:1 Silverspark. On the flip side, a 2.5"-3" wheel would get good speed and torque from that same 50:1 Sliverspark, but would fry the 11:1.

Bigger wheels=Higher gear ratio. Smaller wheels=Lower gear ratio.

Pushers and wedges need a fair bit of speed and torque to get around and bully other bots, so they tend to have mid to low ranged gear ratios. They also tend to have four motors to get even more power.

Spinners do not need much speed, but they do need a fair bit of torque to move around at a reasonable pace. Top speed is not important, acceleration to that top speed, is.

Lifters and flippers are about in the middle. They're more about getting the weapon around, but they also need the moxie to push an opponent if needed.

Remember that voltage influences speed as well. Doubling the voltage doubles the speed of the motor, but may reduce the motors lifespan. Adding more voltage also means the motor will demand more amps, as well as boosting overall power.

You'll want enough torque to spin the wheels freely at a hard push. If you can drive your bot against the wall and the wheels freely spin regardless, you're doing it right. A locked motor is an unhappy motor, and an unhappy motor will suck a load of current from your battery, fallowed by it promptly catching fire. If you've seen the AC suicide scene in the Brave Little Toaster, its pretty much the same thing.

You'll want to be at max speed by the time you hit the center of the arena, or just about. My ant Inch-Up(Two 22:1 Sliver sparks, 2.25" wheels, 7.4 volts), for example, hits its top speed of 3.3mph at around three feet. This may sound slow, but in an 8'x8' arena, I can close the gap on an opponent very quickly. This ( match I had with EXP shows what I mean, even though EXP is faster and more powerful(Four 22:1 Sliver sparks, 11.1 voltage, and I think 1.75" wheels), I'm still able to catch up and keep pressure on him(This match also teaches an another very important lesson, remember to loctite your screws, you dum-dum head  :( ).

For what you're doing, it would probably be better just to stick with the motors you already have and just increase the wheel size, somewhere around 2.5" to 3"(As a bonus, it also acts as sacrificial armor, protecting the motors from damage). If you still need faster motors, then drop down to 33:1 or 22:1 Sliver sparks, depending on how you feel about your driving skill. Unless you already have a fair bit of practice driving, or are really good at F-Zero, I would recommend not going for the 11:1, especially if you don't have the small wheels they require. They're more of a niche gear ratio, as opposed to the more general gear ratios mentioned above.
Title: Re: Getting the right motor gear ratio in a 1lb/3'b
Post by: 65fastbackmaniac on September 20, 2016, 11:53:34 pm
Thanks for the advice it was greatly appreciated.