Reverse Operation

This page will show detailed information concerning how I constructed components used for reverse operation.
There are numerous calculations here, but I try to explain my logic as clearly as possible, if you see an error please contact me.

Be forewarned that typically motorcycles do *not* have a reverse gear, which means that when you construct your Vortex you will either have to be very careful where/how you park, or get out and push! I live in mountainous West Virginia and a reverse gear is not optional, this may vary depending where you live. At this point in time there does not seem to be any drop in solutions available. I have seen numerous implementations from: 1) driving a gear on the rear wheel, 2) driving the rear tire, 3) using gear-motor on jack shaft, and I am sure that there are others.

Next lets do some quick calculations pertaining to reverse gearing - this is what I came up with:
Rear pulleys for the Vortex are between 61-70 teeth, the pulley on the intermediate shaft is between 29-32 teeth. This means that the intermediate shaft will rotate approximately two times that the rear tire turns one revolution (2:1 ratio).

It would seem appropriate that a reasonable reverse speed would be about 2 ft/second. With the circumference of the rear tire being about 75" (24" diameter x PI) then the rear tire would have to turn about 1 rotation every 3 seconds (which equates to about 1.5 MPH). Translating that back to the intermediate shaft then would have to turn about 2 times every 3 seconds or 40rpm.

With a gear motor for a wheelchair that has a full load rpm of about 145rpm, you would therefore have to reduce it using a 3:1 pulley to the intermediate shaft. This would give you the desired maximum speed. If you used a pulse width modulated (PWM) controller you could efficiently control the speed (possibly without having to reduce the gear ratio), from very slow up to the max speed allowed by the motor. Be careful that your reverse speed is not too fast, Jerry Dycus has mentioned that 3-wheelers have tipped over due to overspeed in reverse...

Conversations with other people have also included using: 1) winch motor, 2) trolling motor, 3) starter motor, 4) window motor. Be forewarned that you probably want some sort of DC motor and that there are different types of DC motors from brushed, brushless, etc... You will need to get the proper controller for the type of motor that you will be using!

Where I live in the mountains of WV having a working reverse for the Vortex/Genesis is not an option, it is pretty mandatory.

Since I have started building my Vortex I have put a lot of thinking about how to engineer a reverse solution for my vehicle. Recently I have been thinking a lot more about it as I get into the finishing stages of my vehicle. I have done enough research and design work that it warrented that this be a separate page.

First I wanted to put down some requirements:

• as simple as possible to build and operate
• reverse speed should be variable
• have enough torque to be able to go up a fairly inclined hill
• needs to be separation from the drive shaft

One of the guiding factors that I have been thinking about is that under 'normal' operating conditions (with the vehicle moving in a forward direction) that there has to be some sort of separation between the jack-shaft operation and the reverse motor. When I refer to 'separation' what I mean is that the reverse motor is not being driven by the jack-shaft, but it is stationary.

I have concluded that there are three ways in which to achieve this separation, they are:

1. Physical separation: this assumes that the reverse motor (or coupling) is somehow physically separated from the jack-shaft.
2. One way clutch mechanism: something like using a sprague bearing clutch.
3. Planetary drive: an great example of operation can be found at this website. This mechanism utilizes a 1) sun gear, 2) planetary gears and 3) outer ring gear (also called epicyclic). There is a nice article at Wikipedia.

1) Physical Separation -This solution involves 'disconnecting' the mechanical coupling of the reverse motor and the jack-shaft. This complicates the issue as not only do you have to have electrical circuitry to turn the reverse motor on/off/variate the speed, but you also have to create a mechanical separation as well, and then you have problems in meshing the gears/cogs/whatever. You could use something like a starter motor that has a solenoid to engage/disengage the motor and certainly could be a possible solution.

2) One way clutch - Sprague or other variations of one-way clutches could be used however most of them have a fairly low overrunning speed of between 1,000-2,000 rpm so some sort of gear reducing may need to be done. This complicates the issue, but is not impossible. Actually after thinking about it more a one way clutch by itself will not work - at least by itself without more engineering to do.

3) Planetary drive - these style drives potentially offer a good solution to my problem. The jack-shaft is coupled to say the outer ring gear, the reverse motor is coupled to the sun gear. When the vehicle is being driven in the forward direction the planetary gears are allowed free movement while the sun gear is stationary (reverse motor turned off), this allows the planetary gears to rotate around the sun gear and the ring gear remains stationary. When reverse is desired the reverse motor is engaged and the planetary gears become fixed, allowing the reverse motor to turn the jack-shaft, of course a mechanical linkage would be necessary to lock/unlock the planetary gears. Taking this idea further - you could potentially use a single speed reverse motor and use a brake type of mechanism to slowly 'lock-up' the planetary gears, giving you a variable speed reverse operation!!! Now that I like, and for me it could be the ultimate solution!!!

Here are a couple links showing how automatic transmissions work:

• http://www.mistertransmission.com/transmission_school.htm
• http://www.transmissiondenver.com/facts.html

Ok so I think that you can see that initially I will be exploring further option #3 and fall back to option #1 if it gets too difficult.

Next issue - where are commercially available planetary gear drives? There is a commercial unit sold by Quaife, but it sells for about $1200, this is a bit steep for my tastes it does however look like a good working unit.

After looking hard and long it became very apparent to me that potentially the answer is simple. Literally just about every household has at least one in their garage - a car - specifically one with an automatic transmission. Inside this wonderful piece of technology is one, if not TWO planetary drives. One important fact that I recently learned was that newer vehicles use clutch mechanisms to hold the planetary gear stationary, while older ones use bands! This is a very important fact as the clutch mechanisms require the use of hydraulic pressure, while the band ones can use a mechanical means to engage them.

In talking with my local transmission shop owner more he let me know that older Ford C4, C5 or C6 transmissions as well as Chryslers used bands and for what I was looking for either of them would be the best place to start.

Well in searching the internet I located a C4 transmission and picked it up for $50. Once home I had it apart in no time at all and sure enough there were TWO working planetary drives inside! One towards the front of the transmission, and one at the back, it turns out that the rear one is used for reverse gear in the transmission. The forward gear set is less desireable as the planetary set is designed to always rotate, while the rear one has the capability to lock the planetary gear!

Here is a picture showing the forward planetary drive, fairly simple using three components:

Here is a picture on the left of the assembled unit, and on the right a picture of all five of the components from the rear planetary drive.. The only thing not showing is the output shaft that drives the ring gear (farthest component on the right). The brake band that stops the planetary gear basket from moving on the farthest left:

THIS IS A WORKABLE SOLUTION for variable speed reverse, and a compact unit to boot!

All that is left remaining is:

• a suitable container (with mounting tabs/holes/etc)
• a mechanical mechanism for locking the brake band with variable pressure
• a mounted gear to drive the sun gear (short stubby item)
• some bearings to mount the input/output shafts
• possibly a sprague clutch to keep the reverse shaft from counter revolving
• a flange to mount the DC drive motor

I have been thinking about different ways to make the enclosure for containing the planetary gear unit, and Todd Deahl from ArrowHead Machine shop suggested using a cylindrical enclosure, assuming the proper diameter material can be located. Using a round enclosure would save on fabrication time rather than making a square container box from flat stock. The end caps would still have to be made, in additon probably a protrusion to mount a lever for actuating the brake band, but the total amount of work would be reduced as well as having a decent looking unit when completed.

Once the unit is in place, a lever and cable in the passenger compartment can be used to control the reverse speed, the only other thing needed would be a switch to turn the reverse motor on/off. And finally couple the reverse motor to the unit, and put a drive belt from the unit to the jack shaft.

Here is a thumbnail of one possible solution, click on it to see a larger image:

I did some tooth counting on the planetary unit that I have the results are:

• sun gear = 32 teeth
• ring gear = 70 teeth
• each planet = 20 teeth

I have found the following calculations at How Stuff Works:

• With the Sun gear as input and Ring gear stationary, gear reduction = 1 + R/S : resulting in 3.19:1 (reduction @ Planetary gear)
• With the Ring gear as input and the Planetary gear stationary, gear reduction = -R/S : resulting in 1:-2.19 (overdrive @ Sun gear)
• With the Ring gear as input and the Sun gear stationary, gear reduction = 1 / (1 + S/R) : resulting in .686:1 (reduction @ Planetary gear)

Since I will be using one of the extra solitary Planetary gears welded onto a shaft to drive the Sun gear. By adding this additional gear it makes the output shaft rotation the same direction as the input shaft and the adjusted ratios are changed by 32/20 or:

• With the Sun gear as input and Ring gear allowed to rotate, gear reduction = 5.1:1 (reduction @ Planetary gear)
• With the Ring gear as input and the Planetary gear stationary, gear reduction = 1:3.5 (overdrive @ Sun gear)

So these would be the final gear ratios assuming that the input shaft to the unit is at the same ratio as the jack shaft, or 1:1.

With my suggested jack shaft for maximum top speed (top of this page) of 40 RPM then the reverse motor at the above gear ratio would have to turn at about 140RPM to achieve the maximum reverse speed.

This speed/ratio can be further tweaked by changing the pulley ratio between the jack shaft and the reverse unit. If the unit had a 3:1 ratio to the jack shaft then the reverse motor would have to rotate at 420 RPM to obtain the maximum reverse speed. And further more if a chain/belt was used to connect the DC motor to the unit gearing ratios can also be tweaked.

So by finding a reverse motor that operates anywhere between 50-350 RPM then we can easily obtain our maximum desired reverse speed. If you have a motor that turns faster simply put a larger pulley on the jack shaft and a smaller on on the reverse unit to essential gear it down, don't forget that 40 RPM at the jack shaft is the maximum target speed. I have heard stories that reverse trikes operating in reverse have flipped by going too fast!

I wanted to know at what speed the planetary basket would be turning, so if 'normal' high speed is 60 MPH = 5,280 ft/minute = 63,360 in/minute. The diameter of the rear tire is 75" so would be turning at about 845 RPM and the jack shaft at 1850 RPM. With the 5.1:1 reduction at the planetary gear, the planetary basket would be turning at about 362 RPM. I just wanted to ensure that the planetary gear was not spinning at a high rate when cruising down the road.

The third formula above shows the calculation using the Ring gear as input, but I have not talked about reversing the unit so that the jack shaft is driving the Ring gear - only the Sun gear. From the calculation it is easily seen that using the Ring gear as input from the jack shaft would drasticly increase the speed of the planetary basket, and at top speed of 60 MPH then the basket would be turning at 1,269 RPM instead of 362 RPM, this would be unnecessary and would cause needless wear on the unit.

I spent a little over a day with calipers and planetary gear in hand, and making the first draft engineering drawings of both side plates and input shaft for the reverse unit. By the end of the day they were looking pretty good. I faxed them off to ArrowHead Machine Shop and over the next week or two Todd will try to make the side plates for me in between jobs.

I also found all the bearings and seals that I will be using for it. I am trying to be real careful to list all part modifications, parts to be made as well as a list of miscellaneous components.

Here are a couple of pictures of the finished (and painted) rough prototype:

As you can see one of the shafts (the output shaft) is offset, this shaft connects to the jack shaft. While the centered shaft (input shaft) connects to the DC motor. One of the nice things is that the plate for the input shaft can be rotated in any one of four positions which makes it nice as mounting positions may vary.

On the input shaft side I have also drilled/tapped holes in the case so that a mounting flange could be used for flange mounting of a DC motor. Initially I think that I will be using a couple of flat-belt timing pulleys for output side and a simple shaft coupler on the input side. This makes it very easy to change the DC motor and/or pulleys so that I can see what combinations work the best..

The bolt that you see sticking out of one side is to adjust the tension on the engagement band, iIt will be shortened up so as not to be so obtrusive. Initially I was not exactly sure what the length had to be so I left it long.

Finally at the top of the unit you see an actuator lever that will be cable operated to engage the reverse box.

I now need to make a mounting bracket for the unit to put in onto service on my vehicle, connect it to the jack-shaft and DC motor and then do some preliminary testing. Once initial testing is done any modifications will be incorporated and then I will make a couple of units so that I can judge the level of effort that it will take to make them, and then price it accordingly.

The design that I have does not work in this same manner, and hence can not be utilized the same way. As no power is transmitted through the unit until the band is engaged. Additional design work would be needed if the desire was to put the reverse directly in the path of power from the engine full time, but then again the Quaife unit already does this...

I decided to get industrial sized chain rather than go with motorcycle chain as there are a lot more industrial sized chain sprockets available than motorcycle ones. There are some differences and it's best not to try to interchange them.

In additon the motorcycle sprockets are designed to be mounted on a splined shaft while the industrial versions typically are mounted on round shafts and use a keyway, so installation is easier.

Tonight I looked at how I was going to mount the reverse unit and connect to the jack-shaft and decided that I was going to modify the jack-shaft. Currently it uses three pillow blocks to retain the shaft, and I will be cutting the jack-shaft and using only two pillow blocks.

The reason for this change is that the sprocket that is used for reverse will be right beside the center pillow block, and it is tougher to align three pillow blocks rather than two.

Here is a picture with the bracket in place and then with the reverse unit mounted on it:

I removed the jack-shaft today and shortened it up. Now it extends approx. 3" past the center pillow block. Once out I discovered where all of my drive line noise was coming from. The pillow block that was on the far right side was bad and making a whole lot of noise!

In order to install the jack-shaft you have to slide the outside two pillow blocks inward, put the assembly into place and then slide the outside pillow blocks back out again and bolt them in. The area is just too tight! Once in then you can tighten down the set-screws on the pillow blocks to lock them to the shaft. Removal is the opposite procedure.

I ended up having to cut the jack-shaft with my plasma tourch to even get it out of the vehicle, for some reason after loosening the set-screws I could not move the outside two pillow blocks to get the assembly out. Perfectly honest there is really no reason to have the jack-shaft extend across three pillow blocks, using three of the just seems to complicate things as it is far more difficult to align three pillow blocks than just two, not to mention simply getting the assembly in and out of the vehicle!

When I built the vehicle, right up front I was careful and instead of using plain steel for the jack-shaft I had Arrowhead Machine shop make one up using stainless steel. If you used steel it could easily get surface rust and it would not only be an eye sore but maybe impossible to remove.

I installed a 30T sprocket onto the jack-shaft, this will ultimately be used for connecting the reverse unit, I also have a 24T sprocket in case later I want to change the gear ratio from the jack-shaft to the reverse unit.

Once done re-assembling the vehicle I took it for a test drive - 99% of all the high-pitch driveline noise is GONE! It was a good thing that I decided to shorten up the jack-shaft and discovered the bad pillow block, now it is sooo much better to drive!

A bit more work in getting the reverse operational. First I made up a length of chain to go from the 30T sprocket on the jack-shaft to the output shaft of the reverse unit, I got lucky and the length of the chain came out almost perfect with only a little slack in it, as I did not make ajustment for the reverse box. Ultimately I may put an idler sprocket on it to eliminate any whip and reduce noise (or even better yet use a drive belt:):

Next I made up a mounting bracket for the DC motor out of 3/16" steel. Drilled holes for the shaft as well as the three mounting bolts and put in some 3/8" wide slots about 1-1/4" long to attach the bracket to the engine subframe mount. The slots will be used to take up slack in the drive chain.

Here is a picture of the bracket in place:

Finally I connected the DC motor onto the bracket, this is a 12 volt high torque gear motor with the final output of about 60rpm, it's a bit slower than I initially wanted but will be good enough for now. I had to make up a small spacer for the shaft, as the shaft size is 11mm and the sprocket has 1/2" ID. Next I made up a length of #40 chain and spliced it with a master link to connect the DC motor to the input shaft of the reverse unit. Then I took up the slack and tightened the mounting bolts.

Here are a bunch of pictures of the unit from various angles:

I connected the DC motor up to a battery charger and did some initial testing. It worked quite well and pretty much as expected with the only snafu being the speed of the DC motor being about 1/3 of what it should ideally be. Ideally with the reverse box that I have a DC motor with about 150rpm would be just about perfect.

After this initial testing I don't think that I would want to use any smaller DC motor because even with the 3.5:1 gear reduction in the reverse unit and then an additional 2.5:1 from the output shaft to the jack-shaft the motor worked hard to pull the vehicle over a 2x4 on the ground, while on level ground it moved the vehicle pretty effortlessly. I'm not quite sure how much gradient it will work with but it should be a pretty good start.

Reverse Operation - Getting Closer !

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