In you case if the total value (i.e. all the machines combined) is over $5,000 you need a "Qualified Appraisal" done by a "Qualified Appraiser". You could skip this and if you never got audited your good to go. You don't have to send in the appraisal with your tax return. I was told that donations are a red flag in the IRS's system.
Everything you need to know is the the IRS document below.
Publication 561 (4/2 7), Determining the Value of Donated Property | Internal Revenue Service
I'm looking to donate some equipment and they make it pretty tough. If you read the document they basically say jump through all of these hoops and then we may or may not allow it. Below are the IRS rules for a Qualified Appraiser:
Qualified appraiser.
A qualified appraiser is an individual who meets all the following requirements.
The individual either:
Has earned an appraisal designation from a recognized professional appraiser organization for demonstrated competency in valuing the type of property being appraised, or
Has met certain minimum education and experience requirements. For real property, the appraiser must be licensed or certified for the type of property being appraised in the state in which the property is located. For property other than real property, the appraiser must have successfully completed college or professional-level coursework relevant to the property being valued, must have at least 2 years of experience in the trade or business of buying, selling, or valuing the type of property being valued, and must fully describe in the appraisal his or her qualifying education and experience.
The individual regularly prepares appraisals for which he or she is paid.
The individual demonstrates verifiable education and experience in valuing the type of property being appraised. To do this, the appraiser can make a declaration in the appraisal that, because of his or her background, experience, education, and membership in professional associations, he or she is qualified to make appraisals of the type of property being valued.
The individual has not been prohibited from practicing before the IRS under section 330(c) of title 31 of the United States Code at any time during the 3-year period ending on the date of the appraisal.
The individual is not an excluded individual.
In addition, the appraiser must complete Form 8283, Section B, Part III. More than one appraiser may appraise the property, provided that each complies with the requirements, including signing the qualified appraisal and Form 8283, Section B, Part III.
Your head will hurt after reading it, mine did.