Optimal Direction of the Drill and Chips


Anyone know what is the optimal direction for the drills and chips to spin in? When I say “optimal” I mean, which direction has the higher amount of RPM’s. Also, please specify how you are looking at the motor (for both the drill & chip) - are you looking at it as if the output shaft is pointing towards or away from you?

I figure the drill motor spins optimally in the clockwise direction (when the output shaft is pointed away from you) because that is the direction drill motors do more work. Just thought I would run this by the forum anyways though!

Thanks for your help.

You are correct in your assumption with the drill motors. I don’t know how much slower they spin though, in reverse.

um, i’m pretty sure they both spin the same speed in both directions. considering it’s the same current, driving the same motor, just the other direction

http://www.chiefdelphi.com/forums/showthread.php?t=2140 (Ken Leung and Joe Johnson’s posts)
http://www.chiefdelphi.com/forums/showthread.php?t=23050 (Andy Baker’s post)
http://www.chiefdelphi.com/forums/showthread.php?t=17895 (thread concept)

If you don’t know the answer, don’t reply as though you do.

I’m actually pretty sure the drill motors will rotate at the same RPM’s in either direction, since in an actual drill, the direction of the rotation does not matter, it’s simply reversed. I believe Lord Nerdlinger is correct, that the current is the same in each direction, so the RPM’s will not change, since the gearing is the same. I’m not sure about the chip motors, but I’m assuming they are the same situation as the drill motors.

And if you don’t know the answer, don’t post in support of someone else who doesn’t know the answer!

We’ve gone through this every year guys - The drills are not symmetric, the CIMS are pretty close. Read the old posts - FotoPlasma put them right in front of you, you don’t even have to search for them (heaven forbid anyone would search for an answer first).

In support of Gary and Fotoplasma, the drills most definitely do not spin the same speed in reverse. The reason is the wind angle of the windings. They are biased by about 10 to 15 degrees in order to give better performance while drilling. You can tell when you operate an actual drill that the reverse is slower. There is great debate on these fori about if it matters that the speed is different. Our team thinks the difference is significant enough to make sure the drills are pointing in the same direction.

The CIM motors are close enough to the same speed that we have not done anything specifically to make sure they are pointing in the same direction.


You can test this yourself fairly easily (although following the steps below might classify as a Very Bad Idea). First, put the motor in a clamp or find some other way to prevent it from jumping suddenly. Use clip leads to wire a drill motor to a speed controller (make sure the fan leads on the Victor are wired to the input terminals or to a variable power supply and be very careful to avoid shorts), use clip leads to wire the speed controller to the Maxi fuse block and then to the battery. Obviously you want to use proper wire gages, but for a very short test at no load clip leads should be okay (if they’re not, you’ll know pretty quickly). Attach the PWM cable to PWM-1 on the controller and slowly pull the joysytick forward, and then in reverse. You’ll notice immediately that one direction is definitely faster. Since the leads on the drill don’t appear to be marked, it is possible that you will wire them backwards and reverse will be faster, in this case just swap the +V and GND wires on the output terminals of the speed controller.

All technicalities aside, it is very easy to see that they dont operate at the same speed in forward and reverse. For the last 3 years we’ve uses a 2 drill drive system (3 drill, in 2002) Every year, we could NEVER drive in a straight line, with the exact same gearing for both motors.

Since the leads on the drill don’t appear to be marked, it is possible that you will wire them backwards and reverse will be faster, in this case just swap the +V and GND wires on the output terminals of the speed controller.

Actually the leads of the drills are marked.:slight_smile: If you look carefully there is a postive mark on the one side of the drill motor.

Really? I’ll have to look again. I figured that they had to be but I couldn’t see any markings.

Really? I’ll have to look again. I figured that they had to be but I couldn’t see any markings.

I was fairly sure of it unless I was dellusional. Though it does make sense since hooking those motors up backwards would result in a drill that doesn’t drill very well.

Our team took some measurements with a strobe in preperation for building a quad motor robot. I do NOT believe these numbers actually reflect peak performance, I’m only providing them to give a ballpark idea of what kind of rpm differences were talking about. We used a speed controller ON last years robot (read: we don’t know what our pwm in these tests actually was) and we used fairly dead batteries. Your results may vary… SIGNIFICANTLY.

Tests conducted with 2003 equipment.

Test One RPMs(battery ~11.2V)
Drill in High:
Fwd: 1145 Rvs: 1005
Fwd: 5331 Rvs: 5190

Test Two RPMs(battery ~12.6)
Drill in High:
Fwd: 1244 Rvs: 1094
Fwd: 5670 Rvs: 5560

From memory: Forwards on the Drill was defined as clockwise looking down the barrel, as if you were using the drill. Forwards on the CIM was defined as the opposite. Clockwise as if you were looking at the face of the CIM. Please don’t ask why.

To reiterate: It would be very foolish for anyone to design ANYTHING based on these actual numbers. We recognise that these numbers in some cases don’t even remotely reflect spec. However, if you were wondering if this phenomina is real-- there you go. As for us, we more or less completely disreguarded this data in the consruction of our gearbox; I recommend you do the same.

The drills and chips have optimal RPMs in opposite directions, quite handy in connecting them by a gear.


The difference in no-load rpm of the drill motors has been pretty well covered here, but it should be also be noted that there is also a significant difference in the horsepower the drill motors put out in the two directions. I roughly measured it with a dyno built by one of my team mates few years ago, and there was at least a 10% difference in power between forward and backward. Since we tend to drive our robots in both directions, it may not be worth chosing a motor direction for forward and backward on the robot, but as anyone will know who has driven a robot powered by drill motors only in a “symmetrical-looking” drive train, it IS worth the effort of trying to have both motors turn in the same direction for a given direction of robot travel. The non-symmetry of the Chias is much smaller than that of the drills, though.

Does anyone know if reverse power/speed is a constant (or close) percentage of forward power/speed for the drills, or if a drill in reverse matches a drill in forward up to a certain point? Thanks

seing as how drill motors are desinged to drill holes and tighten fastners and they use a planetery gearbox its alwasys Lefyie loosie rightie tightie.

so rotating right (Clockwise) in the perspective from behind the motor would be the way to Optimualy go

last year, we never had any problems with the motor we were running in forward. The motor assembly we were running in reverse practically melted the whole back end of the motor…one big goop of melted pastic on the back…and we were getting close to destroying the second…it is extremely important that you run them in the same direction…we went out of our way to construct a gearbox soley for the purpose of makign sure both motors were runnign in the same direction