I have made a few drawings for the mechanical parts where all the steering and handling magic happens. After a long time of consideration I am seriously thinking about using a bunch of rubber bands for shocks.
Potential benefits:
If they are put into the right place and right quantity they can make for very cheap and lightweight suspension. Instead of putting the "shocks" in compressive suspension you can use rubber bands in tension which reduces size and weight. Rubber bands are cheap and relatively simple to replace. Also, you can fine-tune your suspension by controlling the number of rubber bands used. If designed correctly the vehicle should be able to continue operations even after all the rubber bands are removed. (It just wont be comfy anymore.) Nylon bungie-cords can be used and may last much longer, however the connections may have to be changed.
Potential disadvantages:
If you lose a rubber band during intense operation it is more probable you will lose more as operation continues. The elements and sun will age the rubber bands after extended use periods. In addition rubber bands lose their stretch over time so more will be required as they get used.
I want to clarify a little bit why I am aiming for suspension. First, I'd like to prove it can be done in tangent with other complex systems such as leaning and steering. In addition to this my (on paper) design is quite short and stands at two feet tall, so there is very little room to add fluffy or bouncy seats to gain comfort. A suspension system may also gain handling advantages over no suspension systems as long as weight addition can be kept to a minimum.
mhodgertt said
Aug 15, 2014
Our team swears by hammock seats. We use a tight nylon web fabric that is very light and suspend it from about the knees to the shoulders and have it so our butt is about 1/2 from the bottom pan. This gives a little comfort and absorbs most of the shock of rough tracks and is very light and comfortable. We have had a couple of suspensions using neoprene bushings so there was a touch of give on the axle to frame area on bumps but not so much it allowed the car to lean outside on corners. This worked OK but most of my students have stated that with the hammock seats they thought it was not necessary and just added one more thing to do and another chance at a failure.
Ron said
Aug 18, 2014
Zach; As a tech inspector I would be concerned about "rubber bands" as suspension...
of course it depends on what kind of rubber band it was.... vintage (and some newer) aircraft use "rubber bands" (1/8 inch diameter synthetic rubber bands) that must be tested (destructive testing) at least ever 2 years... these might be ok as long as I did not see weather cracks...
but "office supply" type bands would concern me, and be inspected with a close scrutiny... if even one band looked bad I would want to see the whole pack replaced... I have seen too many cars with no suspension at all scraping the ground in a race (and pulled out of the race for damaging lap counter grid out here in the northwest) we take damaging the lap counter grid seriously out here.
I wouldn't disqualify a car for having them, but if the car began having a history of "band failure" I definitely would "DQ" the car if I saw poor condition bands before a race when car was inspected (unless band packs replaced before race)
I have an "iffy back" and Mike Hodgert has a decidedly "bad back" and both of us race cars with no suspension at all... he uses a "hammock seat" an I use a combination of "open cell" and "closed cell" foam rubber seat pads to absorb shock.
all in all a suspension system while nice, just is a heavy and complex system that can be circumvented by using a good seat design.
Ron J.
ProEV said
Aug 19, 2014
I would agree with Mike and Ron that, if your goal is driver comfort, it is easier to build a proper seat than a suspension.
A suspension main purpose on a race vehicle is to improve handling. Every bump, especially with the rock hard 110 PSI tires, exerts an upwards force on the corner of the car. With a solid suspension, this force drives the whole chassis upwards, lessening the weight on, and grip of the tires. If the vehicle is trying to go around a corner at the time, it can make the car hard to control.
Rubber bands are a clever, light weight idea. I like the idea of adding or removing bands for adjustability. The challenge, as Ron points out, is that the rubber band's properties will change over time.
To improve a vehicle, it needs to be exactly the same every time you run it. Tire pressure, wheel alignment, chain tension, etc. Then when you change one thing, you can tell if it makes the vehicle faster or slower. Can you come up with a way of setting the rubber band tension, so it is always the same?
The rubber band is the equivalent of a spring. It captures the energy from the bump. It then releases the energy, making the vehicle pogo up and down. So you also need some way of absorbing the energy. On a car, we use a shock absorber or more properly, a dampener. This is an oil filled tube. When the suspension moves, the oil is forced thru little holes. This converts the energy into heat.
A simple dampener would be to tighten the bolts that allow your suspension to pivot. This would increase the friction and act like a dampener but there are numerous practical difficulties with this idea.
A very high tech dampener would be a linear generator. This would capture the energy from the bumps and convert it to electricity and feed it back into the battery. The trick would be to make one light enough to be worth the energy it captures.
-- Edited by ProEV on Tuesday 19th of August 2014 03:33:13 PM
Ron said
Aug 19, 2014
Cliff (ProEV) made a well stated explanation of suspension, I especially like that he explained the NEED for shock absorbers or dampers...
however:
as I understand the rules which govern electrathon, regenerative braking is legal, but a suspension that would charge the battery would not be legal.
(see rule 11.7, page 8 of the 2014/2015 rule book)
besides just like regenerative braking the weight of the system would probably outweigh (pardon the pun) the usefulness of the system.. in other words, more power used to move the extra weight than is returned to the battery.
also: where are you located? if not to far away I could look at your plans and explain why (in my opinion) it might or might not be worth the extra effort to add a suspension.
and please don't think I hate suspensions, I don't... at 50+ years old I am beginning to wish I could take a bit less punishment in my car (I have dropped out of races due to chronic pain issues before) but so far I have not been able to design a suspension that does better (with less weight) than a good seat.
I have made a few drawings for the mechanical parts where all the steering and handling magic happens. After a long time of consideration I am seriously thinking about using a bunch of rubber bands for shocks.
Potential benefits:
If they are put into the right place and right quantity they can make for very cheap and lightweight suspension. Instead of putting the "shocks" in compressive suspension you can use rubber bands in tension which reduces size and weight. Rubber bands are cheap and relatively simple to replace. Also, you can fine-tune your suspension by controlling the number of rubber bands used. If designed correctly the vehicle should be able to continue operations even after all the rubber bands are removed. (It just wont be comfy anymore.) Nylon bungie-cords can be used and may last much longer, however the connections may have to be changed.
Potential disadvantages:
If you lose a rubber band during intense operation it is more probable you will lose more as operation continues. The elements and sun will age the rubber bands after extended use periods. In addition rubber bands lose their stretch over time so more will be required as they get used.
I want to clarify a little bit why I am aiming for suspension. First, I'd like to prove it can be done in tangent with other complex systems such as leaning and steering. In addition to this my (on paper) design is quite short and stands at two feet tall, so there is very little room to add fluffy or bouncy seats to gain comfort. A suspension system may also gain handling advantages over no suspension systems as long as weight addition can be kept to a minimum.
of course it depends on what kind of rubber band it was.... vintage (and some newer) aircraft use "rubber bands" (1/8 inch diameter synthetic rubber bands) that must be tested (destructive testing) at least ever 2 years... these might be ok as long as I did not see weather cracks...
but "office supply" type bands would concern me, and be inspected with a close scrutiny... if even one band looked bad I would want to see the whole pack replaced... I have seen too many cars with no suspension at all scraping the ground in a race (and pulled out of the race for damaging lap counter grid out here in the northwest) we take damaging the lap counter grid seriously out here.
I wouldn't disqualify a car for having them, but if the car began having a history of "band failure" I definitely would "DQ" the car if I saw poor condition bands before a race when car was inspected (unless band packs replaced before race)
I have an "iffy back" and Mike Hodgert has a decidedly "bad back" and both of us race cars with no suspension at all... he uses a "hammock seat" an I use a combination of "open cell" and "closed cell" foam rubber seat pads to absorb shock.
all in all a suspension system while nice, just is a heavy and complex system that can be circumvented by using a good seat design.
Ron J.
I would agree with Mike and Ron that, if your goal is driver comfort, it is easier to build a proper seat than a suspension.
A suspension main purpose on a race vehicle is to improve handling. Every bump, especially with the rock hard 110 PSI tires, exerts an upwards force on the corner of the car. With a solid suspension, this force drives the whole chassis upwards, lessening the weight on, and grip of the tires. If the vehicle is trying to go around a corner at the time, it can make the car hard to control.
Rubber bands are a clever, light weight idea. I like the idea of adding or removing bands for adjustability. The challenge, as Ron points out, is that the rubber band's properties will change over time.
To improve a vehicle, it needs to be exactly the same every time you run it. Tire pressure, wheel alignment, chain tension, etc. Then when you change one thing, you can tell if it makes the vehicle faster or slower. Can you come up with a way of setting the rubber band tension, so it is always the same?
The rubber band is the equivalent of a spring. It captures the energy from the bump. It then releases the energy, making the vehicle pogo up and down. So you also need some way of absorbing the energy. On a car, we use a shock absorber or more properly, a dampener. This is an oil filled tube. When the suspension moves, the oil is forced thru little holes. This converts the energy into heat.
A simple dampener would be to tighten the bolts that allow your suspension to pivot. This would increase the friction and act like a dampener but there are numerous practical difficulties with this idea.
A very high tech dampener would be a linear generator. This would capture the energy from the bumps and convert it to electricity and feed it back into the battery. The trick would be to make one light enough to be worth the energy it captures.
-- Edited by ProEV on Tuesday 19th of August 2014 03:33:13 PM
however:
as I understand the rules which govern electrathon, regenerative braking is legal, but a suspension that would charge the battery would not be legal.
(see rule 11.7, page 8 of the 2014/2015 rule book)
besides just like regenerative braking the weight of the system would probably outweigh (pardon the pun) the usefulness of the system.. in other words, more power used to move the extra weight than is returned to the battery.
also: where are you located? if not to far away I could look at your plans and explain why (in my opinion) it might or might not be worth the extra effort to add a suspension.
and please don't think I hate suspensions, I don't... at 50+ years old I am beginning to wish I could take a bit less punishment in my car (I have dropped out of races due to chronic pain issues before) but so far I have not been able to design a suspension that does better (with less weight) than a good seat.
Ron
feel free to e-mail me musiciansattic@q.com