I am building a life sized prop and I want to have the torso of the prop rotate and raise the arms. For this to be done I realize a high torque servo or motor is needed to raise or turn the prop. I know that high torque servos cost an arm and a leg ($250.00ea) and I am not looking to spend that kind of money…it’s just not in the budget. I read that I could achieve the same control plus the torque needed by using a wiper motor. Is this possible and how?
Thanks in advance
Hi, Jaimyjay,
Good luck with your prop. I have built some operating stage props in my time including a full size B-17 under repair with spinning propellor, a gun turret to launch a human cannonball over the audience, and a gimbal mounted flight trainer that kept my mouth level with the rest of my quartet. I sympathize with your challenge.
I hope I am doing you more good than harm. I am going to suggest you consider using an automobile power window motor instead of a windshield wiper motor. With no specific data, I think you will find better speed, torque, continuous rotation, and mounting characteristics for your job. (In either case, they should be cheap at a salvage yard, and they worked before the crash, right?)
As luck would have it, the Jan 2012 issue of Servo has an extensive article by Gordon McComb on page 38 about the Parallax MadeUSA robot which uses two power window motors. I don’t suggest you should pay nearly $900.00 for the kit just to throw most it away. However, the artcle does discuss some powering and controlling approaches you might want to adopt or modify as suits your project.
If you can’t find the magazine, the article says you can find a listing of separate components at the “MadeUSA page on the Parallax.com site.” Good luck with that because navagating the Parallax site is not as straightforward or intuitive as Lynxmotion’s. [Kudos to Snailkeeper 
] By wonderous feats of pluck and perseverance, I was able to find a .pdf file with the parts and diagram at the following URL:
parallax.com/Portals/0/Downloads/docs/prod/robo/roboaccessories/28975-RobotBasefor12VMotorMountWheelKit.pdf
This file is out-of-date because MadeUSA is now made of thick polyethelene, not plywood, but the rest seems right.
Whether or not this is helps you any, I think many of us would be interested in videos of your prop when finished. Have fun! 
If the torso only has to rotate, then a large motor probably isn’t needed if the torso is designed and mounted properly. The trick is to have the servo only move the component and not support it. The torso could be placed on something like a lazy susan, a caster bearing, or even on a verticle shaft and just have the servo move it. Back in the day a 805BB servo was probably the upper limit for inexpensive servos, but now there are lots of inexpensive servos like below that appear to have a lot of torque.
hobbyking.com/hobbycity/stor … 20sec.html
hobbyking.com/hobbycity/stor … _103g.html
hobbyking.com/hobbycity/stor … 16sec.html
hobbyking.com/hobbycity/stor … _150g.html
