power transmission NOT using gears/chains?

[KenWittlief]

BTW - the best way to drive a bot with no gears or pulleys is to use a motor that spins at the RPM you need for your wheels.

There are several electric scooters on the market now, with the motor designed into the hub of the wheel itself.

Of course, we have to live with the motors that FIRST gives us :c(

[sanddrag]

Originally posted by KenWittlief
when you pedal a ten speed, as long as the wheel is going slower than the pedals, the pedals stay engaged. If you go down a steep hill, and dont pedal faster, then the pedals are just spinning, and the back wheel is going faster, right?

Only drawback, you cant go backwards, unless you add a reverse gear.

If I'm not mistaken the majic behind that is called a one-way bearing. Interesting how you described it being applied to a robot. Instead of the one-way bearing, what about something like manual locking hubs on an old 4x4 truck/suv?

[KenWittlief]

I dont think its called a one way bearing, its more of a cog. Ive taken them apart to grease them. It looks like an inside gear, with the teeth square on one side, and sawtooth shaped on the other.

The tab that engages it is spring loaded - when you pedal forwards it catches, when you pedal backwards the tabs slides on the sawtooth shaped edges.

Now that I think of it, the high speed motor doenst need this, only the high torque motor. So you could have a two motor tranny and use the high speed motor to go backwards when you need to.

[Al Skierkiewicz]

More accurately, this is a one way clutch. It is the same design as a ratchet wrench. The wrench is just able to change direction as well as apply power in one direction and slip in the other.

[Jnadke]

Originally posted by KenWittlief
The tab that engages it is spring loaded - when you pedal forwards it catches, when you pedal backwards the tabs slides on the sawtooth shaped edges.

Now that I think of it, the high speed motor doenst need this, only the high torque motor. So you could have a two motor tranny and use the high speed motor to go backwards when you need to.

As said above, this is a one-way clutch. However, there are a few problems with your design:

1. The high-speed motor would be constantly operating in near-stall condition when accelerating, wasting a lot of electricity.

2. No reverse direction, unless you use a shifting clutch design that reverses the rotation of the gears. You cant just have the one-way clutch on the low-speed motor, because when you rotate the clutch in reverse, the engaging mechanism will catch. Think about it.

[KenWittlief]

Its ok if the high speed motor is always engaged - if you know the speed of the robot, you can contol the power to each one seperately - and you wouldnt 'lean' on the high speed motor until your speed was within its desired range.

and when you reverse, you would power both motors - the high torque motor would freewheel (not catch) and the high speed motor would have all the load. You would not have a lot of torque in reverse, but you could at least back up when you need to

or maybe you could use the ratchet wrench mechanism - make it reversable - then you have high and low torque in forward and reverse directions - you just need to have a shift button, like a car does.

The more I think about this idea, the more I like it. Its simple and easy to implement.

[Jnadke]

Although I am certain you could make it work, the design is turning out rather complex. Overall, if you put the drill (in high) along with the chiaphua directly to a shaft, with the chiaphua on the clutch bearing, the free speed of the chiaphua is 3.5x the drill. This is probabaly the simplest method to make it work. Then just gear it down from there to the output shaft.


It might just be easier to use the Thunderchickens 2002 CCT. With the stronger motors, and higher current constraints, coupled with the use of a worm gear with a 11 degree lead angle, it might solve the problems they were having. The overall theory is quite similar to what you are trying to do, but how it works is very different.

[KenWittlief]

but putting two motors on one shaft, then gearing it all down after that, gives you a high torque, low speed drive train

that is the whole point - you can have the drill motor, geared down low (top speed of maybe 5 MPH) and the chalupa motor, geared up around 10 or 15 mph

and you will have a drive train that will be able to spin tank treads on carpet when you need to move mountains

and fly like the wind when you need to be fast

all without any shifting, and without overloading any of your motors.

[sanddrag]

Why is everyone thinking of having one motor engaged only some of the time? Besides current draw, I can't understand how this would be advantagous over having all the motors engaged and powered all the time.

[KenWittlief]

to get lots of torque, like you want to play king of the hill, you need your drive train geared way down

if you gear a motor way down then you cant drag it up to a higher speed with a second motor - it can only go so fast and that is your top speed

to go fast you need to be geared up - to have both on your drivetrain you need a transmission that can shift gears, or a variable speed transmission.

Using this one way 'ratchet' clutch idea lets you have two motors, geared at the oppose ends of torque and speed, without the need to shift gears on the fly, or to stop and shift gears.

thats why! :c)

[KenWittlief]

Its kinda the same idea as the solid rocket boosters on the space shuttle - they give lots of thrust for the first minute, then they disengage and the rocket on the shuttle itself provide less thrust, but higher speed, to reach orbital velocity.

[DougHogg]

I am wondering if any of this could be applied to our robot for post season competitions.

We are using the 2 CIM motors with custom non-shifting gear boxes and chains going to 2 set of wheels. We shift to high gear by lowering 4 large wheels and raising the 4 small ones.

We have one motor that we aren't using in our drive train or one of our 3 arms: a drill motor.

I had thought of using it like a rocket booster. I guess we could change the gears on our wheels so our CIM motors would give us higher speeds and then use the drill motor as a low speed pusher that would rachet at high speed. Alternately, we could use the drill motor as a booster for high speed and "not lean on it" at low speed. I personally don't have the experience/knowledge to design it. Also it seems tough to stick something like that into an existing robot. However any ideas would be appreciated.

(There are pictures of our robot and our drive train on our web site as listed below.)

[Jnadke]

Originally posted by sanddrag
Why is everyone thinking of having one motor engaged only some of the time? Besides current draw, I can't understand how this would be advantagous over having all the motors engaged and powered all the time.

The Chiaphua alone spins at a free speed of 5,500 RPM with a stall torque of 2.45 Nm. The Drill motor spins at a free speed of ~20,000 RPM with a stall torque of 0.80 Nm. As you can see, the easiest way to set this up would be to put the Chiaphua on a clutch bearing, and gear both motors to a shaft with no reduction. Then, you'd gear from there normally as if you were gearing the chiaphua alone for high-torque. It'd be easier, however, to do it the other way around and use the drill with bosch gearbox, for compactness. A 50:1 gear ratio is a lot harder to create than a 15:1 gear ratio.

As for your question, the reason you wouldn't want to operate the high-speed motor all the time is because, in the area of the high-torque motor, it is going to draw anywhere from 80A to 120A. Obviously, the motor will trip a few breakers. Also, in this range the motor is less than 30% efficient. A lot of the current is going to waste heat. As you know, as a motor heats up, its resistance becomes higher. Therefore, as the high speed motor heats up, it becomes less powerful. Also, more heat means you're closer to letting the magic smoke out.

[Madison]

Originally posted by KenWittlief
Its ok if the high speed motor is always engaged - if you know the speed of the robot, you can contol the power to each one seperately - and you wouldnt 'lean' on the high speed motor until your speed was within its desired range.

Couldn't you establish a correlation, in programming, between the output values of your high speed motor and your high torque motor?

So, rather than operating the high speed motor at near-stall loads under 12V, you could 'artificially' slow it down by applying less voltage via the program.

The free-speed we associate with each motor is for 12V only. If we reduce the voltage to the motor, we reduce it's free-speed. So, if I understand how this might work and what you are saying correctly, it's possible, I think, to make it so the high-speed motor sees little load at low speeds by matching it's potential free-speed to the actual speed, under-load, of the high torque motor.

Does that make sense?

Edit: I really like this idea.

[KenWittlief]

M.Krass - yes, you have the right idea. You could also drop the voltage (PWM output) to the high torque motor when the robot is going fast, or even stop it completely - since its not engaged, its only spinning and wasting power.

The thing I like about this idea the most, you could do this without the oneway clutch (ratchet) with gears and/or chain drive , and to make it a two speed self shifting tranny, all you need to add is one moving part - the little spring loaded cog level thingy.

One extra moving part - you cant get any simplier than that! :c)