Hey Nick,
Thanks for the article. I made a few notes while reading it, hope you don't mind some feedback.
I wasn't able to find free copies of the main references, so apologies if what I mentioned is covered in those, but your article is fairly brief without much detail so it is hard to tell. I hope this doesn't read as though I am having a go at you, it is not intended that way. Just trying to make sure you have the best chance of success, so I thought I would point out a couple of things.
Here goes:
"Best" Case Assumption
You generally appear to be assuming best case for your calculations: blue sky, no wind, flat, shallow snow etc.
- It would be wise to evaluate things when they are stacked against you. Like overcast, headwind, steep hill, deep snow.
- Or are you plan on just running when the conditions are nice, and hunkering down or avoiding the bad conditions/environments?
Solar Input
- make sure you are realistic on what good, average and bad days might be like
-
Ref [4] had some good data on this. ( They also said there MPPTs were not suitable and ditched them, might be good to find out why)
- The way you pivot your panels along the long axis of your vehicle will limit the ability to be perdendicular to the sun, depending on which direction you are travelling.
- Therefore input power will obviously be less than ideal
Second set of Panels
- depending on how you mount these they may limit your ability to tilt the panels
- therefore restricting tracking, or ability to reduce wind loading on the vehicle
Wind
- 5-10m/s wind on the surface appears to be quite common.
Ref: page 9 - Table 2
- You can also get really really high winds. So you may need to have some way of ensuring you can survive these. With a lightweight/high surface area vehicle this could be a serious issue.
- Wind can obviously add drag (eating into you power budget), but it will also try to tip the vehicle causing some wheels to sink more in snow. Which may upset your power calcs.
Terrain
- how realistic is an assumption of 5cm. You should plan to be able to plow through the deep stuff
- How steep is it likely to get? You need to make sure your drive train has enough torque/vehicle thrust to not only plow through the snow, but haul your fully laden vehicle up and over obstacles
Sinkage Calculations
- the way your paper is written suggests a lot of assumptions in the variables you have entered. I hope you are not being too optimistic
- Obviously get some real test data off your own in the snow, before you head south.
- And pick the teeth out of your references data, to make sure you can rely on it.
Weight
- I hope your calculations assumed a fully laden vehicle @ 270kg, with supplies etc.
- How heavy is your steel chassis, is it worth considering aluminium to shave weight. Since weight has such a big impact on the power to plow through the snow
Batteries
- I am not familiar with cold weather performance of batteries, but from your post above it sounds like you are aware of the issues.
-
Here is a reference from a quick search that includes some SAFT Li-Ion data from the Mars Rover at -60C, with battery capacities at 1/8th the capacity of room temp tests.
- bottom line you will need to keep the batteries warm, and need to budget some insulation & power for this task.
Heat
- You will probably have to manage heat very well to use waste heat wisely to keep batteries, and human happy
- You may have to allocate some of you power budget to this, depending on which heating strategy you pick. Of just keeping the vehicle happy, or if you are trying to keep the human happy too (along with the condensation issues Xrain already pointed out)
Anyway that is my 2 cents worth. I am sure you are already aware of most of this, so sorry if this is all old news.
Cheers, Adrian
