Help with power wheelchair modifications

[Jcontoni]

TL;DR Summary

I need more power!

I have a jazzy pride 1121 power wheelchair that I need help with. I have installed larger tires so I wasn't limited to where I could take it in my yard. Because of the increased size of the wheels, it now lacks the power to climb inclines. I was told that possibly a more powerful controller or perhaps different motors may do it. Does anyone have any experience or recommendations how I could solve this issue. Thanks for your help.

 

[FactChecker]

Does it have gears that you can change? If you can put a smaller gear on the motor side or a larger gear on the wheel side (or some combination of that) it might work.

 

[anorlunda]

@FactChecker is on the right track -- changing gears. But it would be difficult for us to say how practical that is without seeing the construction details of your wheelchair.

Can you post the make and model of wheelchair? Do you have diagrams of the power train in the owner's manual? Can you post pictures of the underside showing the motor and drive train?

 

[Jcontoni]

I thought of that and I opened the motor transmission to find it very neatly packed. I thought in order to put a smaller gear on the drive side, I would need a larger gear to match up to it on the other side but there is no room. The case is tight. I couldn't find much information on line and was hoping maybe someone is familiar with this. If there are any plug and play parts that might interchange with my motors or controller or perhaps another way with programming. It's beyond my knowledge on this matter but I'm innovative and trying to learn. thanks for you response

 

[Lnewqban]

Welcome!
The stability of the chair and the power of the brakes should have decreased as well.

This is the manual, which contains a schematic of the motor-reducer assembly:
https://www.pridemobility.com/pdf/owners_manuals/intl_jazzy/uk/uk_jazzy_1121_om.pdf

Could you post a picture of the modified chair?

 

[Jcontoni]

The brakes seem to be fine. The stance I have widened with wheel adaptors I made on a lathe and I also mounted larger wheels and mounts on the rear tires. I have a small lathe and mill in my basement. Attached are a few photos. thanks for your help!

 

[Lnewqban]

The tire's radius or distance between shaft and contact patch seems to have increased about 20%.
I would check the electrical contacts and the carbon brushes of the motors and the state of the battery first.
If feasible, I would reduce the slope of the ramps you normally use.
As a last resort, I would try to find and use a power source delivering above 12 volts.

 

[Jcontoni]

I have disassembled and cleaned the motors along with 2 new batteries. I believe these are 24v motors. This chair is for my father who I'm trying to give access to more of his property off the driveway and sidewalks. The smaller tires don't have the traction or stability needed.

 

[Lnewqban]

I see.
He may fing ondulations of the terrain or natural obstacles like rocks and fallen branches that would require a greater effort from the motors, once in a while.

The problem of modifying the electrical part seems complicated and expensive.
Higher torque motors will draw more amps when some seriuos torque is required, overloading the electronics of the control and reducing the battery top voltage time.

I know you have tried other ways, but what about relocating the motor-reducers to a lower position and finding tires, with same diameter than original ones, but with a more "off-road" pattern?

 

[berkeman]

Summary: I need more power!

I have a jazzy pride 1121 power wheelchair that I need help with.

Have you contacted the manufacturer's Customer Support to see if they have options or suggestions? That seems like your best approach to get this right.

 

[DaveC426913]

I thought in order to put a smaller gear on the drive side, I would need a larger gear to match up to it on the other side

I don't see why this would be the case. A smaller gear on the drive side should not require a larger gear on the other side.

 

[jrmichler]

Welcome to the world of cascading changes of a tightly packaged design. Larger tires need more drive torque. One way to get this is to use the same motor with a different reducer that has a larger gear reduction ratio. Such a reducer, if one is even available, might not fit into the space of the existing gearmotor. Your idea of changing gears in the existing reducer is theoretically possible, but the practical reality is that it is almost always much more expensive than changing reducers.

Or you can increase the battery voltage, which will reduce motor life and could burn up the controller. Or you could fit a more powerful motor to the same reducer, which will shorten the life of the reducer if the controller will even deliver the necessary current. Or you could upgrade the gearmotor, controller, and battery. But that would not fit into the available space.

Have you looked into all terrain wheelchairs, sometimes referred to as rough terrain wheelchairs? There are a number of wheelchairs available that are specifically designed for unpaved terrain with steep slopes. Here is one that was randomly chosen from a search for all terrain wheelchairs:

 

[Jcontoni]

I don't see why this would be the case. A smaller gear on the drive side should not require a larger gear on the other side.

 

[Jcontoni]

The smaller gear would have a smaller diameter so it would no longer align to the larger gear. The axles are fixed in a very tight gearbox.

 

[Jcontoni]

Welcome to the world of cascading changes of a tightly packaged design. Larger tires need more drive torque. One way to get this is to use the same motor with a different reducer that has a larger gear reduction ratio. Such a reducer, if one is even available, might not fit into the space of the existing gearmotor. Your idea of changing gears in the existing reducer is theoretically possible, but the practical reality is that it is almost always much more expensive than changing reducers.

Or you can increase the battery voltage, which will reduce motor life and could burn up the controller. Or you could fit a more powerful motor to the same reducer, which will shorten the life of the reducer if the controller will even deliver the necessary current. Or you could upgrade the gearmotor, controller, and battery. But that would not fit into the available space.

Have you looked into all terrain wheelchairs, sometimes referred to as rough terrain wheelchairs? There are a number of wheelchairs available that are specifically designed for unpaved terrain with steep slopes. Here is one that was randomly chosen from a search for all terrain wheelchairs:
View attachment 302451

Hi, thanks for the reply. I have considered an all terrain wheelchair but they are too costly. I can build and fix many things and I thought it would give me an opportunity to build this for my father. I'm an OK welder and fabricator and have most tools at my disposal so it seemed like an interesting project. If possible I would like to move forward with this longer and maybe an idea will surface. The existing wheel was 11" in diameter and 3" thick and I have converted it to a 16" diameter wheel that is 8" wide. Thanks for your help and interest in my project.

 

[Jcontoni]

Have you contacted the manufacturer's Customer Support to see if they have options or suggestions? That seems like your best approach to get this right.

I have and they have no interest in helping me modify a chair. There are liability issues and I understand. I was hoping someone knowledgeable in wheel chairs would stumble into this thread. It's a fun project for me for my father. thanks for your interest

 

[berkeman]

I have and they have no interest in helping me modify a chair. There are liability issues and I understand.

Hmm, and PF should not worry about liability issues in helping with this project because... ?

 

[DaveC426913]

The smaller gear would have a smaller diameter so it would no longer align to the larger gear. The axles are fixed in a very tight gearbox.

Of course. I had it in head that they were linked by chain, not directly enmeshed.

 

[Tom.G]

Since you increased the wheel radius over 68% from the original, to get the same hill climbing ability you will need to increase the torque applied TO the wheels also by 68%.

That is a big ask for an existing power train! You can either change the gearing, thus slowing down the top speed (which was increased by the larger wheels), or increase the existing motor current by 68%. (Motor current is proportional to torque.)

If the motor current is increased then the motor will run much hotter and will probably self-destruct if run that way for an extended period.

That large a current increase will also require a heftier controller, the existing one most likely does not have that large a safety factor designed into it.

And then the batteries must be considered, the higher the load current the shorter the load-life of the batteries, the will have to replaced more often.

It looks like the only reasonable modification is change the gear ratio between the motor and wheels. Perhaps a chain drive could be added between the existing gearbox and the wheels, taking care to consider how to keep the chain clean.

Sorry

I do like your efforts though. Please keep us updated on this project.

Tom

 

[jrmichler]

It looks like the only reasonable modification is change the gear ratio between the motor and wheels.

I agree, and for the reasons he stated. Another factor to consider is that the larger wheels carry the load farther out. The wheelchair is more stable in the sideways direction, but the bending moment on the gearbox output shaft is increased. That increases the load on the output shaft bearings, which shortens their life. It also increases the chance of breaking the output shaft.

You might consider mounting the wheels on separate axles, with the axles mounted to outboard supports. Then you could mount gears to the gearbox output shafts driving gears mounted to each wheel. An internal gear arrangement like this would keep the wheelchair at about the factory height, with no change in response to the speed controls:

Benefits to this approach are that the load on the gearbox stays the same, the wheelchair speeds stays the same, the wheelchair height stays the same, and the power required stays the same.

 

[Baluncore]

The general rules for wheel size are; If the ground is soft and boggy, lower the tyre pressure, widen the tyres, or use double wheels. If the ground is hard and rocky, increase the wheel diameter, or manicure the path.
The larger external wheel, (or circular track layer), shown above by jrmichler can solve both those problems. There are other, more subtle solutions, like the Dreadnaught wheel. Both those schemes make it possible to reduce the size of the directly driven wheels, which has the effect of lowering the gear ratio, while maintaining the vehicle height, and improving traction.
https://en.wikipedia.org/wiki/Dreadnaught_wheel

 

[Rive]

I'm an OK welder and fabricator

Kind of a cheat, but did you thought about patching up a second hand mower?
Some of them is quite a beast if it's about terrain, and you can get some of them with 'stick as steering (if that's a requirement).