Matching Drill and Chiaphua

[sanddrag]

If I want to design a drivetrain to have both a drill motor and a Chiaphua motor linked up, it would be very easy to match the no load speed of the motors. However, when under the same load, the motors would not have the same RPM because their torque speed curves are different. If under the same load the drill was spinning at 100 rpm and the Chiaphua was spinning at 50 RPM, Not considering a reduction, would the system average out and spin at 75 RPM? What I'm afraid of here is that even though the motors will be turning the system in the same direction, one being faster and the other being slower while both under load will cause them to fight. You cannot match RPMs from 0-max for all different load conditions so how should you match the RPMs. Where on the torque/speed curves should you gear the motors to match RPM?

In a nutshell, will adding the Chiaphua motors to a drill motor drive system have a significant increase in power over just the drills alone?

Also, if someone could address the first paragraph that would be very helpful to us all. Thanks.

[Rickertsen2]

you could use the optical sensors to build tachometers and then adjusty the speed through programming

[nwagers]

I think it would be a far more complex to match the curves... I don't think that they would fight each other unless the loaded speed of one motor is greater than the no load speed of the other. The only question I have is the effieciency

I'm no expert but I this is what I speculate:

The combined speed would be higher than the loaded speed of the slower motor by itself. The motors would balance the load between them on some ratio based on their torque and speed curves. The low speed motor(A) would do part of the work, because the higher speed motor(B) normally spins faster, it adds more power. Since B is now outputing power it increases the speed. The speed increases and A spins faster because B now has part of the load. This would come to a balance at some point for each voltage supplied

You can attempt to match the curves slightly by scaling the output variables to each motor. I don't, however, see the need to do this. I find it hard to believe that you will need more power than a drill or CIP can provide.

[WakeZero]

Originally posted by nwagers
I find it hard to believe that you will need more power than a drill or CIP can provide.

Hehe, I point to the Beatty vs. Kingman match in last years Championship Semi-Finals. My old team (Gila Monsters) clashed with Rage while the two power houses hit head on. Both of their machines were geared for power (well, Beatty had feet for their power)... if one had just a little more, they would have won the pushing match.

As long is there is competition, competitors will seek more power

[Parks]

We did this in our drive system last year and it worked - well.
We had an extremely strong drive system.

The way to do it is to create your own gear box - as far as I am concerned that is the only way it should be done.

Last year, the drill motor contributed roughly 70 percent of the power and the Chipuwah 30. A substantial increase.

It may not be necessary to have that much power in this game but we are doing it anyway because we like it.

If you have questions either post a reply or e-mail me.

cheers

[Andy Baker]

Originally posted by sanddrag
Where on the torque/speed curves should you gear the motors to match RPM?

We have had good experience in trying to match the free speed RPMs.

So...

CIM free speed RPM = 5,500
Drill rpm = 20,000

ratio difference = 20,000/5,500

Then, try to buy the gears that fit this ratio. The key is finding gears which can be delivered quickly that have the right face width (3/8 is safe) and the right ratio. If the gears you can get are approximately the same ratio (+/- 10% of the ratio you calculate), then you should be OK.

Also, you need to allow efficiency losses as you run through your gear meshes. Usually, if your gears are smooth and mounted correctly, you need to figure 95-97% efficiency for each stage.

Andy B.

[Bill Becker]

The two motors will not fight unless you reach an extreme condition where you go outside the max torque of the weaker motor. They will simply operate at the same speed but apply different torques/power based on the curves. It is helpful to plot the geared curves (that match no-load rpms) on the same graph to see how this will work.

I find it hard to believe that last years drill motor would have carried higher loads last year unless your chiapua gearbox efficiency was bad since it had significantly more power.

Has anyone found the ratings for this years drills???

[Stephen Kowski]

Keep in mind that the new drill motors are now running at 40A and the Chalupas are still running at 30A plus the fact the drill motors are now 1/2 inch so you are going to be having to accelerate your chalupa motors ALOT to keep up with those drill motors. Oh, and one more little thing if u do end up doing this you are going to wasting batteries right and left. Good Luck

[Matt Reiland]

Originally posted by Stephen Kowski
Keep in mind that the new drill motors are now running at 40A and the Chalupas are still running at 30A plus the fact the drill motors are now 1/2 inch so you are going to be having to accelerate your chalupa motors ALOT to keep up with those drill motors. Oh, and one more little thing if u do end up doing this you are going to wasting batteries right and left. Good Luck

Rule 2.5 Shows both the Drill and CIM at 40A

2.5 Motor Electrical Overload Protection
When installed properly, the Drill motors and CIM motors are protected by 40 Amp auto-resetting
circuit breakers. Since the motors are capable of drawing over 100 Amps at stall torque, operating
the motors at high torque for more than a few seconds will trip the auto-resetting circuit breaker.

Also why do you state the a 12v 1/2" Drill will accelerate much faster than a 12v 3/8" drill? Usually when people refer to a 1/2" drill, they are referring to the robustness of the transmission( and housing) being greater than a 3/8" drill.

[Andy Baker]

Those 40A breakers can also be used with the CIM (Chalupa) motors (reference page 10 under "the robot).

So... those batteries will be depleted even faster!

Andy B.

[Andrew]

We have had good experience in trying to match the free speed RPMs.

So...

CIM free speed RPM = 5,500
Drill rpm = 20,000

ratio difference = 20,000/5,500

If you do the math, you get about a 4:1 difference between the two (assuming that the Chip has the same characteristics as last year's). Amazingly enough, this is the same GR as the first stage of this year's DM GB (Zsun = 15, Zinternal = 45, Zplanet = 14).

We're planning on building a first stage for the drill motor, where the output shaft and mounting configuration will mimic the Chip. The GB after that will be identical (x4).

Andrew, Team 356

[SiliconKnight]

Hrm ... I wonder what the implications are if we were to match the peak *efficiency* RPM?

Another thing to think about: You want your motors to be running between 25 to 50 % of the motor curve (good design rule). So wouldn't it make sense to gear to match RPM in that zone?

-=- Terence

[Andrew]

I'm shooting from the hip, here, so don't crucify me if I'm passing out bad information.

I'm fairly sure that, in the ideal DC motor, the torque versus speed curve is linear. In this case, you should get the same result regardless of where you perform the matching. In reality, none of the "linear" parameters are linear. I was under the impression that motor specifications arrive at the extreme point by projecting mid-range data. In this case, even if the linear assumption is wrong, the extreme values are projections of the mid-range values and using them in design is OK.

Further, you need to match parameters within some tolerance of good enough (say 10%). The coupling between the motors through the ground will cause the two motors to accommodate.

I'm confident enough in these assumptions to undertake a design. If it turns out to be a disaster, we can always throw away the CIM's.

We should be using a sprocket and chain on at least one of our drive motors. This would allow us to perform some ad hoc matching/tweaking.

Andrew