Does anyone happen to know the dimensions of the tamiya gearbox types
70103 Universal gearbox.
72001 Planetary gearbox.
I’d like to know the overall dimensions and the distance between the shaft an the mounting surface.
The reason I’m asking this is because I have a project with small dimensions and cannot decide which of the top mentioned gearboxes will fit.
By a strange coincidence, I have both, and only, those two Tamiya gearboxes at work, and I can measure them for you on Monday. If your space is tight, the universal gearbox is significantly smaller than the planetary, which isn’t obvious from their individual pictures, but this might help a little:
Do you know the gear ratio you plan on using? The length of the planetary gearbox changes depending on how many of the planetary transmission “slices” you add on.
Well the project is as follows. I’m planning on building a retractable navigation screen that uses a 7” touch screen. The gearbox will be called upon to rotate a 600gram screen about 90 degrees. Obviously the rotation speed should be as low as possible and the torque as high as possible. The speed can probably be controlled with PWM.
Your help on the matter would be deeply appreciated.
I’ll be waiting for your measurements (overall dimensions and distance from shaft to mounting surface).
One other thing, how hard is it to rotate the output shaft be hand if the motor is not powered?
Thanks for your time
Last question first, with the minimum two planetary gear trains of the Tamiya planetary gearbox in series, it is just barely possible to backdrive the motor by hand. With three or four it can’t be done, and it feels like the plastic parts will break before the motor spins.
I can’t tell if the universal gear boxes can be turned backwards because the gears from mine have been scavenged (sorry, I forgot about that) but in general, worm gear mechanism’s beyond a very small gear ratio aren’t back-drivable (has to do with the contact angle and coefficient of friction between the worm and worm gear, very neat stuff!).
Next question, the distance from center of output shaft to mounting surface of the planetary motor is ~0.675". Without the pieces to assemble I can’t say what the distance is from the output shaft to the mounting surface of the universal gearbox is, but if you look at the picture on the back of the box:
you can see that it depends on the orientation of the worm and worm gear stage of the motor. Judging from the picture and the size of the motor itself I’d say the minimum orientation is about 1/8", and the max is similar to the planetary gearbox.
For overall dimensions I took this picture, with the motors on a half-inch grid:
If you want the full-size image is here:
Now that you have the information, a word of caution. These two gearboxes are neat demonstration pieces for mechanical concepts, but they’re not exactly professional-grade equipment. With all the stages in series the planetary motor has 10-15 degrees of play at the output shaft, and when driven makes a sort of crunchy noise, like vacuuming kitty litter off the carpet (and it scares my cats about as much!).
I would take the alternative approach: Calculate the torque required of your motor and the speed-range you’re interested in, then look for a motor that meets those needs. I could help you with this if you can make up a rough dimensioned drawing of how you want to set up the mechanism.
As for what Pololu stocks in your size range, look at the Solarbotics gearmotors with the white plastic casings:
Not only do these have actual torque and speed ratings listed, but they each have a built in slip-clutch that will protect the drivetrain if, for example, someone inadvertently leans on the screen. Also they’re all cheaper than the Tamiya gearboxes you were looking at.
If you want position control in a tight space, you could also use a hobby servo. Again, you trade off torque for speed, and as you get into nicer servos your price tag also goes up up up.
The navigation screen sounds cool though, is this for your car? Any more details or is it just an idea at this point.
First I’d like to thank you for your effort.
The main concept of my design can be viewed in the link below.This will be fitted into my car (Mazda6)
The red bracket is firmly attached to the car dash.
The blue bracket swings inside the red bracket and can be positioned into place by the motor. The screen is attached to the blue bracket.
I tried using a Hitec HS-645MG servo and expensive high torque coreless servos (Hitec HS-985MG) driven by a phidget usb-servo controller, but every time that I positioned the screen I could hear a chatter of the servo that was continually trying to adjust itself.
Both of the servos were vary capable of moving the screen with no problem at all but the noise they made when in a neutral position (trying to hold the screen into position) was very annoying. Since the servo always needs a drive pulse to keep its position I could not stop the servos because the screen would fall. The noise was very annoying so I decided that I should move to simple gearbox motors.
Since you mentioned that the gearbox is noisy,the noise that the gearbox makes will only be for 0.5-1 seconds (until the screen is rotated 90 degree upward). After that, the power will be removed since the motor shaft cannot be rotated.
The screen weight is approximately 22oz.
The hitec servos had a torque of 100oz/in.
Do you think that I can overcome the problem with the servos chattering? That would be great because apart from the servo noise, everything else works great.
What type of motor do you think that I need
Thanks for your time. I really appreciate it.
Assuming that the mass of the screen is evenly distributed, and that the motor is aligned with the center of your screen in the out-of-the-page axis in this drawing, it looks to be about an inch between the motor axis and the center of mass of the screen. This is a very convenient arrangement, because as the 22oz screen rotates upwards the maximum torque it applies on the motor is 22inoz. Plus friction plus inefficiencies blah blah blah… For intermittent use you probably want a motor in the 50+inoz range.
The problem with your servo is the rate that they check and correct their positions. Hitec’s analog servos, like the ones you tried, do this 30 times a second, so the screen starts to sag, then gets pushed back, chatter chatter chatter. If you like the precise position control of a servo, Hitec’s digital servos update 300 times a second, for around $50 and up. This won’t completely get rid of the noise, but it will reduce it’s volume and make it more of a whine than a chatter.
The Solarbotics gm2 or gm3 gearmotors would be a good low-cost solution, especially with the slip-clutch protecting the geartrain. At full 5V, either of these would rotate the screen 180 degrees in about a second. I don’t have any at my fingertips right now, but I remember having one where the clutch started slipping right around when the geartrain would budge when I tried to turn it by hand. The clutch on these slips at 60in*oz, so you should be good.
If you want something robust that really can’t be back-driven, you might try one of the Jameco gearhead motors. I have some 56:1 gearheads that I can backdrive by hand with some difficulty. This one:
is in your size/torque range and has a ratio of 167:1, so it will probably stay quite put with the screen in place (I’m not 100% sure of this). This guy would also be nice for you because it’s rated for 12V, so you could run it off your 6’s electrical system.
Very cool project. My friends at work are all gearheads (VW’s and RX7’s) so I’m just starting to get my feet wet in this sort of thing. I got a USB GPS reciever for Christmas, and I’ve been thinking of hacking a computer into my car to use it. The simplest way I can figure to do this is just with a small laptop, but that’s already more money than I want to spend. Any recomendations? It’ll be the baddest Jetta wagon you ever saw!
Thanks for your invaluable information. I really appreciate it.
I’ll be looking around for the type of motor that you suggested.
I’ve been fouling around with the carputer for about 2 years know.
A lot of people have gone the laptop route and if you have one lying around then go for it. I’m using a small VIA EPIA 12000 motherboard at the moment. It runs OK and can do the basics like mp3, DVD, video and navigation. Just don’t ask it to do the fancy stuff like 3D graphics and flash. If you are really interested, come over to the mp3car.com forum for a real insight on carputers. I’m over there with the same nickname. I’ll be glad to help you out if you need any help with your install.
Thanks for your help.