Has anyone figured out the gear ratio to pair the Drill motors and Chiaphua motors?
We’ve worked it out to 3.5 to 1 to gear down the drill motor, but not confident in that ratio. Any input would be appreciated.
Thx
The no-load output of the drill motor and gear box in high gear is about 1000 rpm. The no-load output of the supplied cluster gear with the Chiaphua motor is about 1100 rpm. Probably the easiest way to gear the two together would be to use those two outputs and gear them together at approximately a 10/11 ratio.
Good luck
If you’re talking about matching the output speeds of the Chiaphua and drill motors by themselves, then I’m certainly happy to see that you got 3.5 as the ratio- I got 3.6.
-Ian Mackenzie
Team 188
We are looking into pair the drill motor without it’s designated gear box.
Does your 3.6 gear ratio take account for spur gear meshing loss. I did not factor it in for my 3.5 ratio.
If you take the ‘official’ no load rpm listings for the drill and Chiaphua motors, 20K and 5.5K respectively, the ratio is 3.636363636363636363636363636363636363636363636
the 3.6 to 1 gear ratio is for the no load, max rpm correct? Wouldn’t varying loads and speeds alter the necessary ratio to keep them in sync? What happens if they do go out of sync, how badly will it effect driving?
*Originally posted by Joseph F *
**the 3.6 to 1 gear ratio is for the no load, max rpm correct? Wouldn’t varying loads and speeds alter the necessary ratio to keep them in sync? What happens if they do go out of sync, how badly will it effect driving? **
The 3.6 ratio is for no load and might not be the ‘perfect’ ratio to use under load conditions, but it should be close. Last year we used drill and FP motors connected 1 to 1, not be the ‘ideal’ setup, but it worked pretty well. We used the same pwm inputs to the speed control for both types of motors. If you have a large mismatch, you might need to use different pwm outputs and ‘throttle back’ the motors that are geared higher.
There is no ‘synchronization’ of the motors that they have to be in. Mainly, you want both types of motors to run in the same portion of their rpm/torque/current curve, and you should avoid gearing too high. It is good to go fast, but not if it means breakers tripping and smoking motors.
If you gear the motors in question 3.6 to 1, the machine should drive fine if the design would drive ok with any other motor arrangement.
Last year we paired the FP motors with the drill motors and ran into problems burning up motors when we needed lots of pushing force. Like when approaching the ramp moving both goals. My guess is our ratio was to steep but I have not done the calculations yet. We would burn up the FP before the drill. Any input?
Thx
Matt White
team 451
Can someone post a picture of two motors mated as described in this thread. Thanks
The Fisher Price (Mabuchi actually) motors are more likely to get toasted mainly because it is less efficient at getting rid of its heat than the Drill motor (made by Johnson, just to add confusion).
The cooling fan on the Fisher Price is less effecient and the way that scaling works, for the size of motor that the FP is, it would have to have much less power to stay the same size (By the way, I expect that the Chiaphua’s will stay much cooler than the drills for similar reasons).
Bottom line: We have used both drills and Fisher Price motors on our drive systems of a number of years. I can count the drill motors we have smoked in one hand with fingers to spare. I may have to take off my shoes to count the number of Fisher Price motors we have gone through.
JOe J.
In addition to the better cooling of the drill motors vs the FP’s that Joe describes, the 30 amp breakers are better ‘protection’ for the larger drill motors. The FP motor could be stalled or nearly stalled for several seconds before the breakers would trip, not a good thing for the motor. A stalled drill motor will trip the breaker very quickly. Of course, you shouldn’t be stalling motors, but it can happen even if you don’t intend for it to.
One of our FP motors failed almost immediately when we lost a pwm signal to the drill motor’s Victor on one side of our drive train, resulting in power to the FP motor only.
Our drive train last year used a drill motor and an FP motor coupled end-to-end and driving a drill gearbox for each side of a track drive.
Ok here’s a monkey wrench for the gears (wah wah)
how about gearing the drill motor down to the chalupa then running that through the drill motor gear box?
possible? worth it?
The gearbox for the drills is designed for about .65 N-m input torque. As the TechnoKats have proven, you can make them work with about 50% over torque (a drill motor plus a Fisher Price motor).
But…
If you slow the drill down to the 5500 RPM free speed that the Chiaphua has and then ADD the Chiaphua to the input to the drill gearbox, you will be inputting something like 4 N-m to a gearbox designed for .65!
Let me know before you turn on the power as I would like to have me safety glasses on…
Joe J.
*Originally posted by Joe Johnson *
**The gearbox for the drills is designed for about .65 N-m input torque. As the TechnoKats have proven, you can make them work with about 50% over torque (a drill motor plus a Fisher Price motor).But…
If you slow the drill down to the 5500 RPM free speed that the Chiaphua has and then ADD the Chiaphua to the input to the drill gearbox, you will be inputting something like 4 N-m to a gearbox designed for .65!
Let me know before you turn on the power as I would like to have me safety glasses on…
Joe J. **
Well… that said… would it be better to gear up the Chiaphua to 20,000 RPM and stick both it and the drill motor into the transmission (100% over torque?), or would it be better to gear both motors past 20,000 rpm, and stay in-spec for torque? How fast can you make that poor little transmission’s input spin, anyways?
I suppose that you might get away with gearing up the Chiaphuas and stuffing both into the Drill Trans.
One one problem is going to be inertia. You may be able to get away with the static loads, but the rotary inertia of the two motor (and gearing) may cause a very large dynamic loading condition.
For example, if your robot hit a brick wall and the wheels stopped very fast. The gearbox would have to stop the armatures of the motors. This can be a very large force. I typically use a fudge factor of 2 to account for the higher dynamic forces. But in this case, perhaps a higher fudge factor would make more sense.
Shifting must be pretty important for so many folks to be thinking about putting so much torque into so little of a transmission 
Joe J.
The motor rotor inertia is a huge factor in dynamic loading. The factor is for like 3 or 4 to 1 when you run into a wall (or other robot). Picture this: Your 20,000 RPM motor is cruising along and BAM!! all of a sudden it has to go to 0 RPM in no time flat. Severe loading condition. As more of us realize we need more power (ie more motors) we will find various ways to couple the motors and if we are not careful, drive trains will shatter from the collision load and the reason will not be obvious. Normally, when things break one would look at the output, because of the higher loading; but if dynamic collision occurs (we call it E-stop in the industrial robot world) the smaller high speed components may be more prone to failure.
Last year’s game gave us a false sense of security when it comes to linking motors together. The TechnoKats did an awesome job last year with their dual motor design, but I believe (and I bet Andy has pondered this very thought) that the dual motor design may fail under collision loads due to the very high motor rotor inertia of the Fisher-Drill motor. Anyway, this is a real concern and should be thought about.
-Paul