Drivetrain help

[thedillybar]

I need some help...wondering if the following will work.

Attach a drill motor to each of the rear wheels.
Attach a chippewa motor to each of the front wheels.

Gear the chippewa motor down to the same free speed as the drill motor in low (300 rpm).

We would leave the drill motor in low when we want torque and shift it to high when we want speed. If we ran all 4 motors at full speed (with the drill motors in high (free speed of 1,000 rpm)), would the wheels attached to the chippewa motors drag or roll freely? Is there anything we could do to help this situation?

Please reply if you can help,
Matt Cuttitta
Team #894

[Jon Lawton]

I am not totally sure if this would work... but it is an idea I've been tossing around my team:

-Gear Chiaphua motor *up* to drill motor's free-speed of 20,000 RPM (1:3.64?).
-Send output of drill motor and Chiaphua motor to drill motor transmission.
-"Four-Wheel-Tank-Drive," the output of the tranmission goes to a double-hubbed shaft. Each hub has a chain to one wheel. (We did this last year with just a drill motor, worked well).
-Repeat for other side of robot.

Now, my only questions are:

-Will the tranmission handle the torque? I think so... we've seen the Fisher-Price and drill motor go through the drill motor tranmission without a problem... the input torque shouldn't be much higher in this case.
-Will we pop the breakers too much? The dual-motor assembly claimed to not trip breakers because the current was distributed among a number of breakers... BUT the Chiaphua motor has a stall current of roughly double that of the Fisher-Price. Of course, the output of the Chiaphua could always be toned-down in the pBASIC code...

Warning: This is *NOT* my area of expertise... can somone with more know-how in this matter comment on the viability of this idea? 8)

[Kit Gerhart]

If you gear the chip motors to match the drill motors in low gear, there would be very high drag from the chip motors if you run the drill motors in high gear. If you want to shift gears with the drill motors only, you should gear the chip motors to match the drill motors in high gear. Then, when you run the drill motors in low gear, you can use separate PWM outputs to the chip motors and run them at maybe 40% the power setting of the drill motors. You can experiment with this. You would want the chip motors to be pulling a little, but not anywhere near 'full throttle' when the drill motors are full throttle in low gear.

I don't know what kind of gearing you plan on running, but if you gear for not over 10-12 feet/sec in HIGH gear, you should have wheel spinning/tread sliding power from the drill motors in LOW gear without much help from the chip motors. I know that from our experience. Having the chip motors there will give you you much better high speed performance when the drill motor gearboxes are in high gear. You should be able to gear even higher than the 10-12 ft/sec I mentioned if you're running the four motors, but you will be getting into shakier territory in regard to overheating motors and possibly tripping breakers.

I hope this all makes sense. If you have any questions, let me know.

[Kit Gerhart]

Originally posted by Jon Lawton

-Gear Chiaphua motor *up* to drill motor's free-speed of 20,000 RPM (1:3.64?).
-Send output of drill motor and Chiaphua motor to drill motor transmission.

Now, my only questions are:

-Will the tranmission handle the torque? I think so... we've seen the Fisher-Price and drill motor go through the drill motor tranmission without a problem... the input torque shouldn't be much higher in this case.
-Will we pop the breakers too much? The dual-motor assembly claimed to not trip breakers because the current was distributed among a number of breakers... BUT the Chiaphua motor has a stall current of roughly double that of the Fisher-Price. Of course, the output of the Chiaphua could always be toned-down in the pBASIC code...

Warning: This is *NOT* my area of expertise... can somone with more know-how in this matter comment on the viability of this idea? 8)

Since the chip motors have about the same torque as the drill motors AFTER GEARING THEM UP, I suspect it might be really pushing things to run both a drill and a chip motor through the drill gear boxes. It might handle it, but...

We ran tandemed drill and Fisher Price motors through the transmissions last year with no problems, but the chip motors are a lot more potent than the F/P motors. If you do the Chip and drill motors through the transmissions, let us all know how it goes. It would be an awesome setup if nothing breaks.

[Jon Lawton]

Originally posted by Kit Gerhart


Since the chip motors have about the same torque as the drill motors AFTER GEARING THEM UP, I suspect it might be really pushing things to run both a drill and a chip motor through the drill gear boxes. It might handle it, but...

We ran tandemed drill and Fisher Price motors through the transmissions last year with no problems, but the chip motors are a lot more potent than the F/P motors. If you do the Chip and drill motors through the transmissions, let us all know how it goes. It would be an awesome setup if nothing breaks.

Hrm... well, how about two transmissions, one on the Chip, and one on the Drill? They would have to be shifted in tandem, and it would add more complexity, of course, but that sounds like a safer way to go? Do you think it is worth experimenting with one transmission? Actually, does anyone know where we can find the specs on the drill motor transmissions? Thank you very much for your input!

[Kit Gerhart]

Originally posted by Jon Lawton


Hrm... well, how about two transmissions, one on the Chip, and one on the Drill? They would have to be shifted in tandem, and it would add more complexity, of course, but that sounds like a safer way to go? Do you think it is worth experimenting with one transmission? Actually, does anyone know where we can find the specs on the drill motor transmissions? Thank you very much for your input!

Using two transmissions would be a possibility. Also, if you are making a tranmission, you might design the home made gearbox to be strong enough to handle both the drill and chip motor. Then you would only need to shift one set of transmissions. If you did that, you might want to use the drill trans in high gear to get about 1000 rpm for the input to your home made transmission. The cluster gear that comes with the chip motor should turn about 1125 rpm with no load.

I don't know the specs of the drill transmissions, but maybe they are out there somewhere. (Joe J.?) I think the ratios are published, but I don't know about torque handling specs. From our experience, though, they rarely break, but 'grinding gears' will damage them is fairly short order.

A disclaimer:
I am not much of a 'nuts and bolts' designer, but I am knowledgable about characteristics of DC motors and how they behave when used to power robots, etc.

[Madison]

By coupling the Chiphua motor to the drill motor before the transmission, am I correct in believing you're attempting to couple a shaft to that tiny little nub of the drill shaft that protrudes from the back? . . . like the TechnoKats motor mounts from last season?

I'm a bit scared of doing that with my team, so we were considering gearing the Chiphua motor output to the drill motor output after the output stages of the drill gearbox. As such, we'd have to keep the drill in either a low or high position with no possibility of shifting via the transmission, though we don't expect that to be a problem for us.

Are there any inherent risks or problems to this approach that I'm ignoring completely? I'd like to think this is easier than coupling before the drill transmission, but my experience with drive trains is limited, to say the least.

[Jon Lawton]

Originally posted by Michael Krass
...
By coupling the Chiphua motor to the drill motor before the transmission, am I correct in believing you're attempting to couple a shaft to that tiny little nub of the drill shaft that protrudes from the back? . . . like the TechnoKats motor mounts from last season?

...

Yike! No, we aren't *that* brave. We want to a make a gear box to gear the Chiphua up to 20,000 rpm. The output of this is tied to the output shaft of the drill motor (with a regular gear, on the front) in a 1:1 ratio. Another gear, of the same size as the other two, is put on the same chain. The shaft this sits on goes to the transmission. Of course... if we go with the two-transmission idea, it is the same thing, save for the gears not all connecting until *after* the transmissions. Hrm... that sounded kind of confusing. I wish I knew the CAD programs better so I could draw it up. But I hope that was able to clear it up some?

ALSO: I was talking to Ken Leung about this and he warned me that there would be a lot of energy loss... I'm wondering: How bad would it be (somthing I'd have to find out by experementation?).

If anyone else has cool ideas on how to get all four motors to play nicely in a flexable design, I'm *very* intrested!

[Madison]

Originally posted by Jon Lawton


Yike! No, we aren't *that* brave. We want to a make a gear box to gear the Chiphua up to 20,000 rpm. The output of this is tied to the output shaft of the drill motor (with a regular gear, on the front) in a 1:1 ratio. Another gear, of the same size as the other two, is put on the same chain. The shaft this sits on goes to the transmission. Of course... if we go with the two-transmission idea, it is the same thing, save for the gears not all connecting until *after* the transmissions. Hrm... that sounded kind of confusing. I wish I knew the CAD programs better so I could draw it up. But I hope that was able to clear it up some?

Okay, I think I follow it better now. I was assuming (incorrectly) that you would have the drill motor transmission attached directly the drill motor itself as it would be were the whole thing assembled for commercial use.

[Kit Gerhart]

Originally posted by Michael Krass
By coupling the Chiphua motor to the drill motor before the transmission, am I correct in believing you're attempting to couple a shaft to that tiny little nub of the drill shaft that protrudes from the back? . . . like the TechnoKats motor mounts from last season?

I'm a bit scared of doing that with my team, so we were considering gearing the Chiphua motor output to the drill motor output after the output stages of the drill gearbox. As such, we'd have to keep the drill in either a low or high position with no possibility of shifting via the transmission, though we don't expect that to be a problem for us.

Are there any inherent risks or problems to this approach that I'm ignoring completely? I'd like to think this is easier than coupling before the drill transmission, but my experience with drive trains is limited, to say the least.

If you want to run without gear change, running the output of the drill transmission and a geared down output from Chiphua motor together should work well. If you are using four wheel drive, you could run the output of the drill gear box to the front wheels and the Chiphua motor output, geared down to match, to the rear wheels or vice versa. If you are using a track drive, you can connect one set of motors to each end or combine the outputs at some central point.

The benefit of using gear change is that you can gear high enough to go very fast in high gear, as long as you are not towing three goals, there are not tugging matches, etc. but in low gear you have tremendous push without tripping breakers, overheating motors, etc.

I suspect that we may have a new 'capability' this year, that of tripping the 60A breakers if we run the drill motors along with the Chiphua motors for our drive train, and are geared too high. This would not be fun, as you watch your robot sit 'dead in the water' for the last 2/3 of a match.