Programmer and programming power wheelchair

[nolanj85]

I am trying to build a wheelchair for my wife with 4 motors for 4 wheel drive to deal with the great outdoors where we live. The problem I have is when you push the joystick sideways the motors work against themselves, one forward and one backwards. Is there anyway to reprogram the motors not to turn in opposite directions? I have tried to change the wiring but than only changes the direction of the motors.

Second question is how did you get the programmer? Did you order it on-line, go to the manufacturer or a distributor? And would you recommend the PC controller version or a hand held one?

[Burgerman]

You are saying If you push the stick forwards and it GOES forwards correctly?
But when you push it sideways it turns the wheels on one (or both) side backwards and forwards at the same time?
Then you have wired it incorrectly!

Sounds like you have one set (say the front set) correct, but the rear set reversed left to right.

The correct setup would be if both of the laft hand side motors were connected together and to the left channel. And obviously the same for the right. Then push the stick forwards and see which way they all go. With it off the ground.

Any that dont go forwards just need the motor connections reversed.
Now test pushng the stick sideways. It will turn all the wheels on each side in the same direction. One side forwards and one backwards.

It may have reversed steering though. At which point you need a programmer. Or swap the left and right plugs at the control box outlet.

You will still need a low level (oem) type programmer though to set up everything including motor compensation. And many other things that are not available on the end user basic programmer.

I ordered my first one direct from Penny and Giles http://www.pgdt.com about 12 years ago. I now have several as each different model and make of control system require different programmers.

If you only have one chair to worry about the hand held units are easier and mobile. If you want to save settings on your PC or do many chairs the PC based versions are better and thats useful!

Hand held versions are not available for some models anyway.

Actually persuading them to sell you a low level version can be difficult if you have no track record or experience though...

[JoeC]

I am trying to build a wheelchair for my wife with 4 motors for 4 wheel drive to deal with the great outdoors where we live. The problem I have is when you push the joystick sideways the motors work against themselves, one forward and one backwards. Is there anyway to reprogram the motors not to turn in opposite directions? I have tried to change the wiring but than only changes the direction of the motors.

Do you mean that when you push the stick sideways, the two left motors go forward while the two right motors go backward? This is how a wheelchair normally steers, and if grip is too great or torque is too low, it will give some noticeable problems when trying to spin in place with four drive wheels. The wheelchair controller does not have any other way to deal with four wheels than to make the front ones behave exactly like the rear ones.

If you look at Burgerman's videos of his four wheeled robot, you can see how the wheels would turn. He only used two motors and a chain drive to work four wheels, but it would be the same type of rotation for you if you did it right.

You can't reprogram to change this, but you can change your thinking a little on how a turn is executed. If the wheels grip too much to pivot in the middle with a hard turning command, then driving forward or backward a bit while turning will cause one side to turn faster than the other, making you drive in little circles. It's not great precision, it might be how it has to be driven.

[nolanj85]

Yes, the two left motors go forward while the two right motors go backward. This works fine if you only use two wheels or 4 fixed wheels, but that limits you indoors/out as it basically hops around and tears the heck out of the ground or the carpet. I tried to compensate that by making the back motors turn on casters but still does not stop the wheels working in opposition to each other. Goal was true 4 wheel drive/steering so it would basically pivot in place

I can probably steer it without turning directly to the side where the motors go in opposite direction. Was hoping I could program out the opposite direction on the rear set but sounds like that is not possible.

If anyone has ideas I am certainly open.

[Burgerman]

That is what its supposed to do!

How can it steer with 4 fixed wheels unless it "tank steers"?

If a tank turns on the spot it also tears up the ground. Thats why 4x4 chairs are only ever going to be of any use outdoors.

I dont understand what you mean by caster? You mean that two of the driven wheels are also castering? Cant be done. Physics wont allow that at least without much complication, computers, shaft encoders and 2 seperate controllers. I dont think?

Eg, going forwards both turn same way. Reverse and initially both go the same way until the caster turns (by castering as they do!) and then it needs to drive the motor the other way while still moving in the same direction... Same when you want to go forwards. And steering will be random depending which way it decides to twist.

Should be "interesting" to drive to put it mildly

I think a slight redesign is going to be needed.

You can have steering like a car that is joystick controlled but casters will never work. Or fixed 4 wheel drive like my robot
http://www.powerchair-review.co.uk/expe ... hair-4.htm

That steers ok on carpet since the wheels are very close coupled, and its pretty wide (26.6 inches). Not much skid at all. Wathch movies half way down page. This is going to be your answer I think?

[Pete]

here are two 4x4 wheelchair designs that might give you a few ideas. One has only front steering while the other has four-wheel steering, the front steering one relies on the motors to pull the wheels left or right by applying more power to the outside wheel. I'm not sure how the four-wheel steer one works as I've never actually seen one in the flesh.

http://www.magicmobility.com.au/
http://www.fourpowerfour.com//index.asp

[Burgerman]

Neither use casters. They steer like a car. One of them at both ends.
The first uses "tank" style steering and allow chassis geometry to turn the wheels.
Second one uses a scooter style controler for forwards and back and a ram for steering. A powerchair controller wont be able to do that.