hey I've posted here once before and I greatly appreciated the responces, they helped out a lot. Now I have another question I can't seem to find much info on the net. I'm doing a senior design project, it's basically a remote controlled lawn mower. I'm using a 6HP engine with a vertical shaft, and was wondering if theres a way to make the mower drive the rear drive axle using a PTO with a combination of a clutch, or something on that line. But I also want the mower to go forward and reverse. I also thought of maybe using a dc motor to drive the rear axle, but I'm trying to think of a PTO drive to help reduce the weight and the clutter of so many components. If anyone has any suggestions or comments, I'd be glad to hear them. Or any other design suggestions would be appreciated Thanks in advance.
Remote control forward and reverse ... with a PTO? You're going to be running electrical power anyway, the clutch(es) are likely going to be electrically powered.
You might want to simply use a DC motor, and reverse the applied voltage on command. You might be able to connect an alternator to the upper-end shaft, where the manual starter assembly / cooling fan are.
Alternately, you could connect a little hydraulic pump... and run the remote control (and solenoid valves) off of battery power.
I had a similar problem when I built a robot out of garden tractor parts for the Robot Wars competition. The solution I used in the end was a hydrostatic transaxle. This is a single unit which does the job of the gearbox, clutch and rear axle all in one. It uses a hydraulic pump connected to a hydrualic motor, and you can vary the rate at which the pump delivers oil to the motor, which in turn varies the speed at which the wheels turn. From the point of view of remote control, the big advantage of these hydrostatic units is that there's just one control lever. If you push the lever forward, the vehicle (confusingly) goes in reverse. Push it further forward and the vehicle goes faster in reverse. Push the lever backward to drive forward normally, and further backward to increase speed. There's a neutral range of a few degrees in the middle. The reason the lever doesn't behave as expected is because it is connected to the driver's control lever through a mechanism.
Because just a single lever is needed to control the entire transmission, it's good for a remotely controlled vehicle. The only problem is that the lever's pretty stiff (takes about 25 Nm to turn if I remember rightly), but I rigged up a system using a car wiper motor connected to the control lever through a geared reduction, and it worked fine. The hydrostatic units were about £205 plus tax (British prices in
1998) and are manufactured by Tecumseh. They're a lot easier to control than traditional mechanical gearboxes, but they'll be harder to fix if anything goes wrong too. I don't know if this information will be of any use to you, but it's a thought. They're certainly very easy to control. If you want any more information just drop me an email. I've got some photos of the system I can dig out if you're interested.
Since you already looked into getting electrical power from the motor in your previous post, a DC motor is your best bet. Use electronics to replace a gear box or other mechanical system for allowing for forward and reverse. This will reduce weight and clutter. If you have the abilities/facilities, there are many options for creating H bridge circuits availible through Google. Also, since this is an rc project, you could spend a few bucks on an off the shelf electronic speed control. If you don't want to go through the hassle of using an alternator, just use a larger battery, you'll need it for your electronics anyway. I guess it all denpends on the focus of the project. If you want to learn about machine design and mechanical stuff, find a mechanical solution. If you want to get into electromechanics, check out the options I mentioned.
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